Cyanobacteria: Gram negative or Gram positive?

Cyanobacteria: Gram negative or Gram positive?

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My (school) textbook states that cyanobacteria ("blue-green algae") are Gram positive (no references provided). They mention this at several points over the chapter we're doing so it doesn't look like a typo.

However, this Wikipedia article on "Gram staining" (under "Gram negative bacteria") states:

Gram-negative bacteria generally possess a thin layer of peptidoglycan between two membranes (diderms). Most bacterial phyla are gram-negative, including the cyanobacteria, spirochaetes, and green sulfur bacteria, and most Proteobacteria (exceptions being some members of the Rickettsiales and the insect-endosymbionts of the Enterobacteriales).

Emphasis, mine.

There is no mention of cyanobacteria under the section "Gram positive bacteria".

I understand that there is a possibility that some cyanobacteria stain positive, and other stain negative (owing to the lack of a very sharp definition for "cyanobacteria", as well as the limitations of Gram-staining).

So what I want to know:

1) Are cyanobacteria generally Gram positive or Gram negative?

2) Are there exceptions to that general trend? If so, what are they?

Cyanobacteria are clearly didermic (two membranes, inner and outer) bacteria, normally classified as Gram-negative bacteria. If your textbook says several times that they are Gram-positive, instead of a typo, you have a plain mistake.

However, things are not that simple.

According to Hoiczyk and Hansel (2000), this traditional classification of the prokaryotic envelope doesn't work well with cyanobacteria, whose cells show a combination of the features of Gram-positive and Gram-negative bacteria:

The multilayered peptidoglycan of gram-positive bacteria, with a thickness ranging from 20 to 40 nm, usually forms a physical barrier for the dye. In gram-negative bacteria, however, with their relatively thin sacculus of 2 to 6 nm, the stain can easily be washed out. Together with other characteristics, such as the occurrence of accessory cell wall polymers or the presence of an outer membrane, the peptidoglycan architecture largely determines the different properties of the two cell wall types in terms of mechanical stability, permeability, and resistance toward chemical substances. Although this classification is generally useful, it oversimplifies the concept of bacterial cell walls. It also ignores, for example, that the largest and perhaps most diverse group of bacteria, the cyanobacteria, possess cell envelopes with a combination of these features. (emphasis mine)

Here is an image (ibid.) comparing a Gram-negative cyanobacteria with Escherichia coli:

Electron microscopical comparison of the gram-negative cell envelopes of the cyanobacterium P. uncinatum (A) and E. coli (B). Both bacteria were identically processed using cryosubstitution procedures. Note the combination of gram-positive and gram-negative features present in the cyanobacterial cell wall, like the thick peptidoglycan layer and the outer membrane, respectively.

Hoiczyk and Hansel (2000) add that…

… Despite their overall gram-negative structure, the peptidoglycan layer found in cyanobacteria is considerably thicker than that of most gram-negative bacteria. (emphasis mine)

In conclusion, cyanobacteria are Gram-negative bacteria. However, their envelope show some features os Gram-positive bacteria. Besides that, there is variation withing the group.


  • Hoiczyk, E. and Hansel, A. (2000). Cyanobacterial Cell Walls: News from an Unusual Prokaryotic Envelope. Journal of Bacteriology, 182(5), pp.1191-1199.

Cell Structure of Cyanobacteria | Microbiology

Like bacteria, the cell of cyanobacteria also consists of a mucilaginous layer called sheath, the cell wall, plasma membrane and cytoplasm.

These are shown in Fig. 4.32 and described below:

1. Sheath:

Usually the cell of cyanobacteria are covered by a hygroscopic mucilaginous sheath which provides protection to cell from unfavourable conditions and keeps the cells moist (Fig. 4.32). Thickness, consistency and nature of sheath are influenced by the environmental conditions. Sheath consists of pectic substances. It is undulating, electron dense and fibrillar in appearance.

2. Cell Wall:

After observing the cyanobacterial cell under electron microscope, it appears multilayered present between the sheath and plasma membrane. The cell wall consists of four layers designated as LI, LII, LIII and LIV (Fig.4.33). The layers LI and LIII are electron transparent, and LII and LIV electron dense.

(i) LI is the innermost layer of the cell wall present next to the plasma membrane. It is of about 3-10 nm thickness and enclosed by LII.

(ii) LII is a thin, electron dense layer. It is made up of mucopeptide and muramic acid, glucosamine, alanine, glutamic acid and di-amino-pamelic acid. The layer LII provides shape and mechanical strength to the cell wall. Thickness of this layer varies from 10 to 1000 nm.

(iii) LIII is again electron transparent layer of about 3-10 nm thickness,

(iv) The outermost layer is LIV which is a thin and electron dense layer. It appears wrinkled and is undulating or convoluted.

All the layers are interconnected by plasmadesmata. Numerous pores are present on the cell which act as passage for secretion of mucilage by the cell. Chemically the cell wall of eubacteria and cyanobacteria are much similar.

The chemical constituent of cyanobacteria and Gram-negative bacteria is the presence of mu-copolymer which is made up of five chemical substances viz., three amino acids (di-amino-pamelic acid) and two sugars (glucosamine and muramic acid) in the ratio of 1:1:1:1:2.

Similar ratio of these constituents is also found in E. coli. However, in some cyanobacteria such as Anacystis nidulans, Phormidium uncinatum and Chlorogloea fritschi the amino acids and sugars are found in different ratios. Moreover, diamino acid is common in all prokaryotes. In addition, lipids and lipopolysaccharides have also been detected in the cells of cyanobacteria.

3. Plasma Membrane:

The cell wall is followed by a bilayer membrane called plasma membrane or plasma lemma. It is 70A thick, selectively permeable and maintain physiological integrity of the cell. Plasma membrane sometimes invaginates locally and fuses with the photosynthetic lamellae (thylakoids) to form a structure called lamellosomes (Fig.4.32). The plasma membrane encloses cytoplasm and the other inclusions.

4. Cytoplasm:

Cytoplasm is distinguished into the two regions, the outer peripheral region which is called the chromoplasm and the central colourless region called centroplasm.

(i) Chromoplasm:

The chromoplasm contains the flattened vesicular structures called photosynthetic lamellae or thylakoids (Fig.4.32). Thylakoids may be peripheral, parallel or central. Besides photosynthesis, thylakoids have the capacity of photophosphorylation, Hill reaction and respiration. Depending upon physiological conditions they are arranged accordingly.

Several photosynthetic pigments such as chlorophyll a, chlorophyll c, xanthophyll’s, and carotenoids are present inside the lamellae. On its upper surface phycobilisomes (biliproteins) of about 40 nm diameter are anchored by a protein.

Phycobilisomes comprises of three pigments: phycocyanin-C, allophycocyanin and phycoerythrin-C. These three pigments harness light in the sequence: Phycoerythrin—Phycocyanin—Allophycocyanin—Chlorophylls.

(ii) Centroplasm:

The centroplasm is colourless and regarded as primitive nucleus devoid of bilayered nuclear membrane and nucleolus. Several grains that can take stain are dispersed in centroplasm. Some people are of the opinion that the centroplasm is the store house of food and according to the others it is an incipient nucleus (Fig.4.32).

5. Cytoplasmic Inclusions:

Several glycogen granules, oil droplets and other inclusions are dispersed in chromoplasm as well as in centroplasm regions:

(i) Cyanophycin:

The cyanobacteria accumulate nitrogenous reserve material called cyanophycin or cyanophycian granules when grown at conditions of surplus nitrogen. These are built with equal molecules of arginine and aspartic acid. These represent as much as 8% of total cellular dry weight. They can be observed under a light microscope as they accept neutral red or carmine.

(ii) Gas Vacuoles:

In many cyanobacteria e.g. Anabaena, Gloeotrichia, Microcystis, Oscillatoria, etc. the gas vesicles of viscous pseudo vacuoles of different dimensions are found.

The cytoplasm lacks vacuoles. The vesicles are hollow, rigid and elongated cylinders (75 nm diameter, 200-1000 nm long) covered by a 2 nm thick protein boundary. The ends of vacuoles are conical (Fig. 4.32). The protein boundary is impermeable to water and freely permeable to gases. Under pressure they get collapsed, and therefore, lose refractivity.

The function of gas vesicles is to maintain buoyancy so that the cell can remain at certain depth of water where they can get sufficient light, oxygen and nutrients. Floating and sinking phenomenon is a key feature found in free floating cyanobacteria. Through this mechanism they can escape from harmful effect of bright light.

(iii) Carboxysomes:

Carboxysomes are the polyhedral bodies containing 1, 5-ribulose bi-phosphate carboxylase (Rubisco).

(iv) Phosphate Bodies:

See volutin glanules of bacteria.

(v) Phycobilisomes:

Some phototrophic organisms (i.e. cyanobacteria and red algae) contain two accessory pigments such as carotenoids and phycobilins (also called phycobiliproteins), in addition to chlorophyll or bacteriochlorophyll pigments. The carotenoids play a photo-protective role, whereas phycobilins serve as light harvesting pigments.

Phycobilins are the main light-harvesting pigments of these organisms. Phycobiliproteins are red or blue in colour. These compounds consist of an open-chain tetrapyroles derived biosynthetically from a closed porphyrin ring. The tetrapyroles are coupled to proteins.

Phycobiliproteins are aggregated to form a high molecular weight darkly stained ball-like structure called Phycobilisomes. The phycobilisomes are attached to the outer surface of lamellar membrane (Fig. 4.34 A).

Phycobiliproteins includes three different pigments:

(a) A red pigment phycoerythrin which strongly absorbs light at 550 nm,

(b) A blue pigment phycocyanin which absorbs light strongly at 620 nm, and

(c) Allophycocyanin which absorbs light at 650 nm.

The pigments in phycobilisomes are arranged in such a way that allophycocyanin is attached to photosynthetic lamellar membrane. Allophycocyanin is surrounded by the molecules of phycocyanin and the latter by phycoerythiin.

Phycoerythrin and phycocyanin absorb shorter (high energy) wavelength of light and transfer energy to allophycocyanin. Allophycocyanin is closely linked to the reaction centre chlorophyll. Thus energy is transferred from allophycocyanin to chlorophyll a. Presence of phycobilisomes makes the cyanobacterial growth possible at the region of lowest light intensities.

(vi) DNA Matrix:

Like other prokaryotes the cyanobacteria also contain naked DNA fibrils dispersed in the centroplasm. DNA material lacks nucleoplasm, and like E. coli contains a histone like protein that binds with DNA. The total number of genomes is yet not known but in Agmenellum 2 to 3 genomes have been reported.

However, base composition of DNA in different cyanobacteria varies, for example in chroococcales (35-71 moles percent G + C), Oscillatoriales (40- 67 moles percent G + C), Pleurocapsales (39-47 moles percent G + C) and heterocystous forms (38- 47 moles percent G + C). The molecular weight ranges from 2.2 x 10 9 to 7.4 x 10 9 Daltons.

Like eubacteria, cyanobacteria also have 70S ribosomes. Similar to bacteria cyanobacteria contain covalently closed non-functional, circular plasmid DNA. These are called cryptic plasmid as the function of cyanobacterial DNA is not known.

6. Specialized Structures of Cyanobacteria:

There are certain specialized structures viz., hormogones, exopores, endospores, Nano cysts, heterocysts, exospores, endospores, akinetes, etc. which are produced in cyanobacteria.

(i) Hormogones and Hormocysts:

Hormogones are the short segments of trichomes produced in all filamentous cyanobacteria. Hormogones are produced by several methods such as fragmen­tation of trichomes into pieces (e.g. Oscillatoria) (Fig. 4.35C), delimination of cells into intercalary groups (Gloeotrichia) (Fig. 4.35A), fragmentation and round off the end cells (Nostoc) (B), formation of separating disc or necridia and their subsequent degradation (Oscillatoria, Phormidium). The hormogones show gliding movement. Each hormogone may develop into a new individual.

Some other cyanobacteria produce hormocysts or hormospores which function similar to hormogones. Hormocysts are produced intercalary or terminal in position. They are highly granulated and cells are covered by a thick mucilaginous sheath. In the cells of hormocysts a large quality of food material is accumulated. During favourable condition hormocysts develop into a new plant.

(ii) Endospores, Exospores and Nanocysts:

The non-filamentous cyanobacteria generally produce endospores, exospores and nanocysts, for example Chamaesiphon, Dermocapsa and Stichosiphon. The endospores are produced inside the cell. During endospore formation, cytoplasm of the cell is cleaved into several bits which are converted into endospores.

After liberation each endospore germinates into a new plant, for example Dermocapsa. When the size of endospores is smaller but larger in number, they are called Nano spores or nanocysts. Some of the cyanobacteria (e.g. Chamaesiphon) reproduce by budding exogenously. The spores produced through this method are called exospores.

(iii) Akinetes:

The members of Stigonemataceae, Rivulariaceae and Nostocaceae are capable to develop the vegetative cells into spherical perennating structures called akinetes or spores such as Nostoc, Rivularia, Gloeotrichia, etc. (Fig. 4.35A).

During unfavourable conditions, the vegetative cells accumulate much food, enlarge and become thick walled. These are formed singly or in chains. Akinetes possess cyanophycean granules hence these appear brown in colour. Under favourable conditions the akinetes germinate into vegetative filaments.

(iv) Heterocysts:

Heterocysts are the modi­fied vegetative cells (Fig.4.35A-B). Depending on nitrogen concentration in the environment, hetero- cyst formation occurs. During differentiation sev­eral morphological, physiological, biochemical and genetical modifications take place in heterocyst.

They are slightly enlarged cells, pale yellow in colour containing an additional outer investment. They are produced singly or in chains and remain intercalary or terminal in positions. These are found most frequently in Oscillatoriaceae, Rivulariaceae, Nostocaceae and Scytonemataceae.

In heterocysts, total amount of thylakoids gets reduced or absent. The photosystem II that generates oxygen becomes non-functional. The amount of surface proteins that combine with oxy­gen and create oxygen tense environment is in­creased.

Rearrangement in nif gene (nitrogen fixing gene) cluster takes place and expression of nitrogenase and nitrogen fixation are accomplished. In addition, these take part in perennation and reproduction as well.


In 1985, the proposed classification of cyanobacteria took into account the Bacteriological factor. The proposal identified four Orders of the bacteria which included Chroococcales, Nostocales, Oscillatoriales and Stigonematales.

Other orders of the phylum that have been discovered include Chroococcales, Gloeobacterales, and Pleurocapsales.

The bacteria also falls under Kingdom Monera and Division Eubacteria. Further classification has however resulted in significant debate at higher taxonomic levels.

* Initially, they were classified as blue-green algae because they possess chlorophyll and algal-like appearance. However, further studies showed that they are prokaryotic, which helped re-classify them appropriately.

Cyanobacteria: Gram negative or Gram positive? - Biology

Above: a computer model of the filamentous cyanobacterium Oscillatoria . Three filaments are shown, each filament being a chain of cells (the cells being disc-like in Oscillatoria ). Cyanobacteria , also called blue-green algae, are a major group of photosynthetic bacteria. Their photosynthetic pigments give them their blue-green colouration (though sometimes other pigments mask this as some forms are orange or red in colour).

The humble cyanobacteria dominated life on Earth for an immense period of time, from about 3 billion years ago to 500 million years ago - what could be called the Age of the Cyanobacteria. This age was crucial for the development of animal and plant life on Earth, since during this time the cyanobacteria created the first oxygen atmosphere. They are still widespread, though often overlooked. Their varied forms, vibrant colours and, in some cases, their graceful gliding movements make them beautiful subjects for the microscope. On close examination, they prove to be much more sophisticated and complex than first impressions might suggest.

The internal structure of a typical cyanobacterium is shown below:

As prokaryotes, the blue-greens have no nuclear envelope and no
true nucleus, instead the DNA is circular and free in the cytosol (cytosol = liquid component of the cytoplasm), though intricately folded and attached to special scaffolding proteins. Typical of bacteria, the DNA is often confined to a central region of the cell, the nucleoplasm , forming a nucleoid . Surrounding this is cytoplasm rich in prokaryotic ribosomes - the riboplasm . The peripheral cytoplasm contains the photosynthetic apparatus. Flattened membrane vesicles called thylakoids house the pigments and proteins that make up the photosynthetic machinery. Each outer cytosolic surface of each thylakoid (the surface facing into the cytosol) is studded with particles called phycobilisomes , which
consist of chlorophyll type a and accessory pigments, called phycobiliproteins , such as phycoerythrin (red) and phycocyanin (cyan). The accessory pigments both screen and protect the chlorophyl from damaging UV light and also trap photons and funnel
them to the chlorophyl, acting as antennae , that increase the wavelengths of light that can be used for photosynthesis.

The photosynthetic membranes, or thylakoids, are not confined inside chloroplasts as in plants and eukaryotic algae (see photosynthesis in plants) but are free in the cytoplasm. They are also single and not stacked as in chloroplasts.

Gas vacuoles (clusters of protein gas-filled rods called gas vesicles) are often present in aquatic forms. These act to regulate buoyancy, helping the cells to float at the right depth in the water column where light levels are optimal for photosynthesis. Cyanophycin granules are large, up to 500 nanometres in diameter, and typically located near the cell periphery. Cyanophycin is a polypeptide (polymer or chain of amino acids) produced by a ribosome-independent mechanism and involved in nitrogen metabolism. Lipid droplets , storing lipids for later use, may also be found in the periphery of the cell. Large polyphosphate bodies are granules that store phosphate and tiny glycogen granules or rods (30 to 65 nanometres in diameter) are situated between the thylakoids and act as a store of glucose (for carbon and energy - a fuel store). Carboxysomes (polyhedral bodies) are 200 to 300 nanometres in diameter and consist of the main enzyme involved in photosynthesis, rubisco (ribulose -1,5-bisphosphate carboxylase).

Cyanobacteria are Gram negative bacteria, meaning that they do not stain purple with Gram's stain. The Gram stain dyes peptidoglycan purple. Peptidoglycan is the polymer that makes up the tough cell-wall layer in the cell envelopes of most bacteria. However, in Gram negative bacteria the peptidoglycan wall is covered on the outside by an additional membrane, the outer membrane, which prevents the gram stain from reaching the peptidoglycan and so this type of bacteria do not stain purple. (In Gram positive bacteria, the peptidoglycan sits on top of the cell membrane, which is also called the inner membrane in Gram negative bacteria, and so is reached by the stain, staining the cells deep purple.) Bacteria have other optional layers in the cell envelope. Cyanobacteria typically have an S-layer, a layer of proteins fitted together like a mosaic, which covers the outer membrane and on top of this is another layer of protein fibrils, called oscillin fibrils, wound around the cell in a helix.

In addition, a thin slime sheath, external to the oscillin layer, encloses the cell or filament. Cyanobacteria may be immotile, or they move by gliding motility . A good example of this is seen in the Oscillatoria filament. These filaments glide along a solid surface, leaving the exuded slime sheet behind them as a collapsed tube as they go. The slime sheath is continuously secreted during these movements. Filaments will also glide vertically within their slime sheaths, an important adaptation in some forms for altering their height above the surface. One of the chief reasons why some bacteria have evolved into filaments of cells is to increase their length, allowing them to reach above the stagnant boundary layer. Gliding also helps cyanobacteria to reach optimal lighting levels for photosynthesis.

Gliding Cyanobacterial filaments appear to be driven by jet propulsion! In oscillatoria, for example, there are rows of pores on either side of the annular groove which demarcates one cell from a neighbouring cell. Slime jets from these pores in a controlled manner, propelling the filaments in one direction or the other. The oscillin channels the slime jets in a helix around the cell, causing the filament to rotate on its axis as it glides. The slime eventually forms a collapsed tube trailing behind the filament, as secretion of new slime continues. The slime is not too expensive to produce, as it consists of polysaccharides (chains of sugar molecules) that expand massively upon mixing with water. earlier authors claimed that slime production was a consequence of and not the course of motility, and controversy still surrounds the mechanism.

More details on bacterial gliding motility .

It is possible that some cyanobacteria contain contractile protein fibres, and these have been implicated in jerking and clumping movements seen in Spirulina , whose filaments are helical.

In Oscillatoria the cross-walls, which divide one cell from the next in the filament, consist of peptidoglycan lined by the inner membrane of each cell on each side. The outer membrane, S-layer and oscillin layer do not extend into the cross-walls, but instead form continuous layers along the whole filament. This means that the periplasm (the 'space' between the inner and outer membranes is continuous along the filament and may act as a channel for communication from one cell to the next. However, in at least some cases tiny pores, called
microplasmodesmata , have been seen to span the dividing cross-walls, connecting the cytoplasms of
neighbouring cells together. These junctions may function as electrical contacts, allowing electrochemical signals (e.g. hydrogen or calcium ions) to diffuse from one cell to the next, enabling the cells to communicate via electrical signals and so synchronsie their activity. This is important if the filament is to move in a given direction - each cell needs to 'know' which direction to move in.

Cyanobacteria may be single-celled, or they form simple multicellular structures, such as the filaments of cells,
also called trichomes , that we have seen in Oscillatoria . In some forms, e.g. Nostoc , the trichomes may be
coiled up inside shared green, black or red mucilagenous capsules called nodules, which may be a centimetre or two in diameter and look like grapes or plums. Sometimes these nodules or colonies are leaf-like. Presumably, this both protects the cells inside and enables them to better optimise the atmosphere that surrounds them. Many types, including Oscillatoria , do not form colonies or nodules. As we have seen, the cells within a trichome may communicate via pore-junctions, a feature of true multicellularity. Filaments are branched in some species and may even consist of more than one row of cells. Filaments are produced when cells divide in one plane only. Some forms divide in two planes, producing square sheets of cells, others divide in three planes to produce cubes or balls of cells.

Cyanobacteria may form larger structures. Stromatolites (stromatoliths) are large columnar deposits of calcium carbonate built-up over immense periods of time by cyanobacteria. The oldest fossil stromatolites are 2.7 billion years old. These columns allow cyanobacteria to maintain a good position close to the source of light, as generation upon generation adds to the stromatolite. They were once common along the coasts of ancient oceans on Earth, when cyanobacteria dominated the biosphere, and are still found in the Dead sea, where the very high salt concentrations prevent growth of cyanobacterial rivals.

Above: a filament of a nitrogen-fixing cyanobacterium such as Ananbaena or Nostoc . The large cell on the left is
a heterocyst , the large granular cell on the right is an akinete (spore). The arrangements of heterocysts and akinetes along the chain are characteristic of the species or strain.

Nitrogen fixation is the biochemical process of capturing and converting atmospheric nitrogen gas into usable organic nitrates. (Fixation is an old alchemical term meaning to make solid). Plants are generally incapable of utilising nitrogen gas, though some plants, such as legumes, harbour nitrogen-fixing bacteria in root nodules, and in exchange for nutrients provided by the plant the bacteria supply the plant with nitrates which the plant can use. In general, plants require nitrogen in the form of soil nitrates which their roots can absorb.

Cyanobacteria are the only organisms able to perform both oxygenic (oxygen-generating) photosynthesis and nitrogen fixation. They achieve both functions by a division of labour - vegetative cells carry-out photosynthesis, whilst specialised cells called heterocysts carry out nitrogen-fixation. Low concentrations of oxygen rapidly and irreversibly inactivate the nitrogenase enzymes responsible for fixing nitrogen, so photosynthesis, which generates oxygen, must be kept separate from nitrogen-fixation. Most of these nitrogen-fixing cyanobacteria are filamentaous and produce specialised nitrogen-fixing cells, called heterocysts . Examples include Nostoc and Anabaena . Heterocyst and nitrogenase synthesis is repressed when combined/fixed nitrogen is already present. Lack of combined nitrogen stimulates heterocyst and nitrogenase production, but if the required nitrogen gas is also absent, then development arrests at an intermediate stage, called the proheterocyst. About 5-10% of the cells develop into heterocysts in a 30 hour period.

Heterocyst . Heterocysts are formed at regular intervals along the filaments. The heterocysts have thick outer wall layers and the thylakoids become concentrated near the cell poles and special polar connections form where the heterocyst is attached to vegetative cells. Their thick walls are thought to restrict oxygen diffusion into the cell, whilst enzymes neutralise any oxygen that does enter the cell. Chlorophyll a is present, but phycobiliproteins are absent. Some components of the photosynthetic machinery are down-regulated (PS II is inactive and rubisco is also lacking, so they can neither fix carbon dioxide nor produce oxygen in the light). [For a description of PS II and rubisco see photosynthesis .] However, some components of the photosynthetic
machinery (such as PS I) are upregulated and these components are able to harness light energy to
manufacture ATP in a process called photophosphorylation . This provides the heterocysts with the energy
needed to fix nitrogen. Respiration uses hydrogen generated during nitrogen fixation (nitrogenase produces one hydrogen molecule for every nitrogen molecule fixed). The heterocyst depends upon the vegetative cells to supply nitrogen, reductant (electron donors) to reduce the nitrogen to ammonium, sugars for fuel and possibly acting as the required reductants, and glutamate, all via the microplasmodesmata. The heterocysts fix nitrogen into ammonium ions which diffuse to neighbouring vegetative cells via the microplasmodesmata, at least some of this ammonium combines with the glutamate to form the amino acid glutamine which is then exported to the vegetative cells (which process the glutamine by removing the nitrogen and turning it back into glutamate).

Only cyanobacteria and some other forms of bacteria can fix nitrogen. This is one reason why flood plains are so fertile: the flood waters leaves behind masses of bacteria, including cyanobacteria, which fix nitrogen and so increase the fertility of the soil.

Anoxygenic Photosynthesis

Non-heterocystous nitrogen-fixing cyanobacteria are facultative (meaning they can do this as an option) anoxygenic photosynthesisers (photosynthesis that produces no oxygen) and fix nitrogen under anaerobic growth conditions. Oscillatoria limnetica , an inhabitant of hypersaline lakes, does not produce heterocysts, but can photosynthesise using sulphide, rather than water, as a reductant (electron donor) and producing sulphur rather than oxygen. Since they are not producing oxygen they can perform nitrogen fixation in the same cells. In the dark they can still produce ATP by respiring their polyglucose food reserves using the sulphur as a final electron acceptor, rather than oxygen. They can also respire anaerobically by fermentation. There are other mechanisms of protecting nitrogenase from oxygen in cyanobacteria that are poorly understood.

Many strains are facultatively chemotrophic in the dark, but these maintain constituitve photosynthetic apparatus and can photosynthesise immediately when light is introduced. Many phycoerythrin-producing strains exhibit complementary chromatic adaptation: when grown in green light they have a high phycoerythrin to phycocyanin ratio, but when grown in red light they have very little phycoerythrin. This response appears to be mediated by a phytochrome-like light-sensitive pigment.

Ecology of Cyanobacteria

Cyanobacteria thrive in aquatic environments, and although all require moisture for growth, many are terrestrial. The surface of desert soils may be encrusted with cyanobacteria, as in the deserts of Utah. These cyanobacteria dehydrate and become inactive when dry but rapidly hydrate and resume growth when moisture is present, producing nodules.

Left: a cyanobacterial filament found growing on
tree bark. Can you spot a heterocyst?

Green snow in springtime glacial regions contains cyanobacteria. Cyanobacteria also occur inside rocks (endolithic cyanobacteria) in Arctic and Antarctic deserts and inside limestone and inside coral rubble and coral sand. Others deposit limestone in reefs and hot springs.

Cyanobacteria occur in the surface waters of stratified freshwater lakes. See purple bacteria for more about such lakes.

Many cyanobacteria form symbioses with other living organisms, such as with fungi in some lichens , with sea squirts (e.g. the cyanobacterium Prochloron , sometimes classified as separate from other cyanobacteria). The chloroplasts of red algae are very similar to cyanobacteria, possessing single thylakoids (not stacked) and chlorophyll a but not chlorophyll b and in possessing phycobiliproteins. The chloroplasts of plants and green and brown algae are different, but still clearly descended from photosynthetic prokaryotes. The ancestors of these chloroplasts must have been taken up by ancestral cells (or else they invaded the ancestral cells) and became endosymbionts, in a similar manner to the evolution of mitochondria . Today we still see all stages in such evolutionary processes, with the cells of some organisms taking up microbes to perform the same roles, sometimes transiently, whilst others live in necessary symbiosis, unable to survive without their symbiotic partners.

Reproduction of Cyanobacteria

Reproduction is asexual, though being prokaryotes mutation rates are high, so new forms can be constantly produced. Cyanobacteria grow by binary fission , in which a vegetative cell splits or divides into two daughter cells which are genetic clones of the mother cell (apart from mutations). Some reproduce by multiple fission, a cell splitting into many tiny spores called baeocytes . Akinetes , such as those produced by Nostoc , are dormant resilient spores which can germinate in suitable conditions to produce a new filament. Some filamentous forms also produce chains of motile cells, called hormogonia (singular: hormogonium) for dispersion. For example, Nostoc , which is generally immotile, produces special gliding filaments called hormogonia that detach from the ends of the parent filament. Filaments may also break, giving rise to two new chains.

Above: Oscillatoria . Below: Oscillatoria- like cyanobacteria exhibiting gliding movements: the uppermost filament was gliding back and forth in its slime sheath. The presence of a definite and fairly rigid slime sheath suggests that this is probably a species of Lyngbya (although some Oscillatoria have thin sheaths and may secrete a mucilaginous coat when irritated). The bottom image is approximately 40 seconds later than the top image.

The tip of gliding filaments often appear to swing or oscillate like a pendulum, but this is apparently due to the fact that the filament rotates as it glides, so that any curvature of the filament appears as a swinging motion.

Note the separation discs in the uppermost filament: these are formed by the death of cells at intervals along a filament, the dead cells filling with mucilage. Filaments will eventually fragment at these separation discs into separate segments called hormogonia or hormogones, a form of asexual reproduction. Although separate filaments may occur, perhaps during dispersal by gliding motility, filaments generally occur as clumps or mats in which the individual filaments may be parallel or interwoven.

Note also that the front-most or apical cell has characteristic morphology, which aids species identification, in this case the apical cell is ovoid.

Above: Oscillatoria from the bottom of a salt marsh. There were considerable differences in size and coloration indicative of different species in the sample. Lyngbya can also escape its sheath and be confused with Oscillatoria. The whole Oscillatoria-Lyngbya grouping is rather artificial and DNA analysis is starting to tease these assemblages into groups with evolutionary connections. Oscillatoria, for example, has been split into several groupings by this kind of analysis.

Experimental procedures

Database search

DNA and protein sequence databases were accessed at the National Center for Biotechnology Information ( and from the Kazusa DNA Research Institute of Japan ( The draft genome sequence data for S. elongatus PCC 7942 were obtained from the Department of Energy Joint Genome Institute (Version 01dec03 Cyanobacterial homologues of known bacterial cell division genes were identified based on amino acid sequences using the Basic Local Alignment Search Tool ( tblastn and blastp Altschul et al., 1997 ). Protein motifs were searched by pfam (

Culture conditions

Synechococcus elongatus PCC 7942 and its derivatives were grown in BG-11 medium ( Allen, 1968 ) in 25 or 125 ml Erlenmeyer flasks or on Petri dishes containing 1.2% agarose at 30°C in continuous light (c. 140 µE m −2 s −1 ) on a rotary shaker. Growth of cells in liquid cultures was measured by determining OD730. For inhibition of FtsI, cephalexin (1 µg ml −1 ) was added to liquid cultures at an early phase of growth (OD730 ≈ 0.1) cells were observed 72 h after addition of the drug.

Transposon mutagenesis

Tn5-692 was transferred to S. elongatus PCC 7942 cells by conjugation with E. coli strain HB101 bearing pRL443 (conjugal plasmid), pRL528 (helper plasmid) and pRL692 (containing Tn5-692) as described ( Elhai and Wolk, 1988a Koksharova and Wolk, 2002 ). Filters bearing exconjugants were incubated for 72 h at 30°C (light intensity, c. 60 µE −2 s −1 ) before transfer to medium containing erythromycin and spectinomycin (10 µg ml −1 each). Spreading colonies identified between 15 and 30 days after the initiation of selection were streaked to new plates. Isolated colonies were used for further experiments.

Determination, by inverse PCR, of the sequences flanking the transposon in the transformants

A single colony was grown in liquid culture containing erythromycin and spectinomycin (2 µg ml −1 each) and the genomic DNA was extracted from 5 to 10 ml of culture (OD730 > 0.5) using a Wizard Genomic DNA Purification Kit (Promega, Madison, WI, USA). The DNA was digested with TaqI or HhaI for 2 h HhaI, when used, was heat-inactivated at 65°C for 15 min. The digested DNA preparations were ligated overnight at 16°C with T4 DNA ligase (Invitrogen). The genomic regions were amplified and sequenced with primers (Q. Fan and C.P. Wolk, unpubl.) based on the sequence of Tn5-692 (GenBank Accession No. AF424805). The primer sequences and reaction protocol are to be published elsewhere but are available upon request. Segregation of mutations was assessed by PCR using primers (Table 3) up- and downstream from the insertion.

Targeted gene disruption

To inactivate a gene, the relevant genomic region was amplified with primers (Table 3) by PfuTurbo DNA polymerase (Stratagene, La Jolla, CA). Each amplified DNA was cloned into the vector pGEM-T (Promega, Madison, WI, USA), and the insert was sequenced to identify error-free clones. The omega cassette (the omega interposon Prentki and Krisch, 1984 cut from pRL453 and pRL463 Elhai and Wolk, 1988b ), which confers resistance to erythromcyin, streptomycin and spectinomycin, was inserted into the target gene at a unique restriction site (Table 3). The orientation of the omega cassette inserted to each orf was determined by digestion with a combination of SpeI, which cuts once in pGEM-T, and SphI, which cuts once in the omega cassette and once in pGEM-T. Constructs in which the antibiotic resistance gene of the omega cassette was inserted in the same orientation as the gene were used for gene disruption, except for orf1939, into which the omega cassette was inserted in the opposite orientation. Gene disruptants were generated by transformation of wild-type cells with these constructs and selected on BG-11 plates containing spectinomycin (10 µg ml −1 ). The single colonies were streaked on new plates five times. Segregation of the mutations was confirmed by PCR using the primers listed in Table 3.


All observations by microscopy were carried out using cells grown in liquid. S. elongatus PCC 7942 cells were collected by centrifugation at 5000 g for 10 min and then observed with Nomarski optics (BH2 Olympus America, Melville, NY).

For observation of nucleoids, cells were fixed at room temperature for 30 min with 1% glutaraldehyde dissolved in phosphate-buffered saline (PBS) and were then stained with DAPI at a concentration of 1 µg ml −1 .

FtsZ localization and nucleoids were observed together by staining cells first with anti-FtsZ antibodies for indirect immunofluorescence microscopy and then with DAPI. Cells were fixed in 3% (w/v) paraformaldehyde dissolved in 50 mM PIPES-KOH, pH 6.8, 10 mM EGTA, 5 mM MgSO4 for 30 min at room temperature and washed twice with PBS. After treatment with 0.05% Triton X-100 in PBS for 15 min, the samples were permeabilized for 30 min at 37°C with 0.2 mg ml −1 lysozyme dissolved in Tris-HCl, pH 7.5, 10 mM EDTA, and then washed twice with PBS. After blocking with 5% bovine serum albumin in PBS (blocking buffer) for 30 min, cells were labelled at 30°C for 2 h with anti-Anabaena FtsZ antibodies ( Kuhn et al., 2000 ) diluted 1:500 in blocking buffer. Cells were then washed twice with blocking buffer, and incubated with Oregon green-conjugated goat anti-rabbit IgG (Molecular Probes, Eugene, OR 1:300 dilution) for 1 h at 30°C. Cells were then washed twice with PBS, stained with DAPI at a concentration of 1 µg ml −1 and observed by fluorescence microscopy (DMR A2 Leica Microsystems, Wetzlar, Germany).


Pellets of cells dissolved in Laemmli sample buffer (50 mM Tris, pH 6.8, 10% glycerol, 2% SDS, 5% 2-mercaptoethanol, and 0.01% bromphenol blue) were incubated at 95°C for 5 min. The samples were centrifuged at 15 000 g for 10 min and the supernatant solutions were subjected to electrophoresis and immunoblotting. Immunoblot analyses were performed as previously described ( Stokes et al., 2000 ) using 10% acrylamide gels. The primary antibody (anti-Anabaena FtsZ) and secondary antibody (horseradish peroxidase-conjugated goat anti-rabbit antibody Pierce, Rockford, IL) were diluted 1:2000 and 1:20 000 respectively.

Sensors in Water Quality Monitoring

Daoliang Li , Shuangyin Liu , in Water Quality Monitoring and Management , 2019

1.6.1 What Is Blue-Green Algae?

Blue-green algae (BGA), also known as cyanobacteria , can range in colors from blues, greens, reds, and black. BGA can reduce nitrogen and carbon in water, but can also deplete dissolved oxygen when overabundant. Monitoring BGA is important because they pose a serious threat to water quality, ecosystem stability, surface drinking water supplies, and public health through toxin production and the large biomass produced in algal blooms.

YSI measures blue-green algae in real time through the in vivo fluorometry (IVF) technique. This method directly detects the fluorescence of a specific pigment in living algal cells and determines relative algal biomass. The BGA sensor does not receive interference from chlorophyll or turbidity.

Biology II Chapter 27 - 2

Organisms that need only an inorganic compounds such as CO2 as a carbon source.

Photoautotrophs (Energy source: Light) and Chemoautotrophs (Energy source: Inorganic chemicals) are included in the autotroph cateory.

Organisms that require at least one organic nutrient, such as glucose, to make other organic compounds.

Both carbon source: Organic molecules

Photoheterotrophs (Energy source: Light) and chemoheterotrophs (Energy source: Organic compounds) are included in this category.

Both require light as their Energy Source.

  • Photoautotroph carbon source : CO2
  • Photosynthetic prokaryotes, plants and certain protists fall in this category.
  • Photoheterotroph carbon source : Organic compounds
  • Certain prokaryotes such as Rhodobacter and Chloroflexus fall in this category.

Chemoautotrophs require inorganic chemicals as their energy source while chemoheterotrophs require organic compounds.

Chemoautotroph carbon source: CO2

Chemoheterotroph carbon source: Organic compounds

Photosynthetic organisms that capture light energy and use it to drive the systhesis of organic compounds from CO2 or other inorganic carbon compounds.

Cyanobacteria and many other groups of prokaryotes are photoautotrophs, as are plants and algae.

Only need an inorganic compound such as CO2 as a carbon source. However, instead of using light as an energy source, they oxidize inorganic substances such as hydrogen sulfide (H2S), ammonia (NH3) or ferrous ions (Fe2+).

This mode of nutrition is unique to certain prokaryotes.

An organism that harness energy from light but must obtain carbon in organic form.

This mode is unique to certain marine and halophilic (salt-loving) prokaryotes.

An organism that must consume organic molecules to obtain both energy and carbon.

This nutritional mode is widespread among prokaryotes.

The conversion of atmospheric nitrogen (N2) to ammonia (NH3). Biological nitrogen fixation is carried out by certain prokaryotes, some of which have mutualistic relationships with plants.

The nitrogen may then be turned into amino acids and other organic molecules.

A specialized cell that engages in nitrogen fixation in some filamentous cyanobacteria formaly called heterocyst.

It allows for metabolic cooperation.

A surface-coating colony of one or more species of prokaryotes that engage in metabolic cooperation.

Cells in a biofilm secrete signaling molecules that recruit nearby cells, causing the colonies to grow. The cells also produce proteins that stick the cells to the substrate and to one another.

Channels in the biofilm allow nutrients to reach cells in the interior and wastes to be expelled.

A phototroph derives its energy from light, while a chemotroph get its energy from chemical sources

An autotroph derives its carbon from inorganic sources (often CO2) while a heterotroph get its carbon from organic sources.

Thus, there are four nutritional modes: photoautotrophic, photoheterotrophic (unique to prokaryotes), chemoautorophic (unique to prokaryotes) and chemoheterotrophic.

The bacterium must rely on chemical sources of energy since it is not exposed to light, and it must be a heterotroph if it requires an organic source of carbon rather than CO2 (or another inorganic source, like bicarbonate)

A prokaryote in the Archaea domain that lives in an environment so extreme that few other organisms can survive there. It includes extreme halophiles (salt-loving) and extreme thermophiles (heat-loving).

"lovers" of extreme conditions (philos, lover)

  • (halo, salt)
  • A prokaryote in the domain Archaea that lives in highly saline environments such as the Great Salt Lake, the Dead Sea, and Owens Lake.

For example, the proteins and cell wall of Halobacterium have unusual features that improve function in extremely salty environments but render these organisms incapable of survival if salinity drops below 9%.

However, this is all relative.

A group of archaea named for the unique way that they obtain energy. They use CO2 to oxidize H2, releasing methane as a waste product. Among the strictest of anaerobes, methanogens are poisoned by O2.

The "marsh gas" found in some swamps and marshes are produced by these archaea. Some other species of methanogens live within the guts of cattle, termites, and other herbivores. They may also be used as decomposers in sewage treatment facilities.

Chemoheterotrophic prokaryotes function as decomposers. They use organic molecules as both the energy source and the carbon source.

Decomposers are any of the saprobic fungi and prokaryotes that absorb nutrients from nonliving organic material such as corpses, fallen plant material, and the wastes of living organisms and convert them to inorganic forms. They are detritivores.

Without the actions of prokaryotes and other decomposers such as fungi, all life would cease.

Parasites that can survive only within animal cells, depending on their hosts for resources as basic as ATP.

The gram-negative walls of chlamydias are unusual in that they lack peptidoglycan. (Similar to Archaea then. )

Helical heterotrophs that spiral through their environment by means of rotating, internal, flagellum-like filaments.

Many are free-living but others are notorious pathogenic parasites.

Photoautotrophs that are they only prokaryotes with plantlike, oxygen-generating photosynthesis.

Chloroplasts likely evolved from an endosymbiotic cyanobacterium.

Both solitary and colonial cyanobacteria are abundant wherever these is water, providing an enormous amount of food for freshwater and marine ecosystems.

Gram-positive bacteria rival the proteobacteria in diversity. These include actinomycetes, some of which are free-living species that help decompose the organic matter in soil.

Also include solitary species such as Bacillus anthracis, which causes anthrax and Clostridium botulinum, which causes botulism.

This is a large and diverse clade of gram-negative bacteria that includes photoautotrophs, chemoautotrophs, and heterotrophs.

Some proteobacteria are anaerobic, while others are aerobic.

It is categorized into 5 categories from alpha to epsilon.

These prokaryotes convert inorganic compounds to forms that can be taken up by other organisms, such as the use of CO2 to make organic compounds.

Also, cyanobacteria produce atmospheric O2 and a variety of prokaryotes fix atmospheric nitrogen into forms that other organisms that can use to make the building blocks of proteins and nucleic acids.

An ecological relationship between organism of two different species that live together in direct and intimate contact.

The larger organism is known as the host and the smaller is known as the symbiont.

For example, human intestines are home to an estimated 500 to 1,000 species of bacteria.

Lipopolysaccharide components of the outer membrane of gram-negative bacteria.

In contrast to exotoxins, endotoxins are released only when the bacteria die and their cell walls break down.

  • Proteobacteria
  • Chlamydias
  • Spirochetes
  • Cyanobacteria
  • Gram-positive Bacteria

Proteobacteria is a large and diverge clade of

a) gram-positive bacteria
b) gram-negative bacteria

Gram-positive bacteria are included in their own group.

This large and diverse clade of gram-negative bacteria includes photoautorphs, chemoautotrophs, and heterotrophs.

Some proteobacteria are anaerobic, while others are aerobic. The phylogenetic tree below shows the relationship based on molecular data.

Species in one subgroup, the actinomycetes, form colonies containing branched chains of cells. Two species of actinomycetes cause tuberculosis and leprosy.

However, most actinomycetes are free-living species that help decompose the organic matter in soil their secretions are partly responsible for the "earthy" oder of rich soil.

The gram-negative walls of chlamydias are unusual in that they lack peptidoglycan.

Both solitary and colonial cyanobacteria are abundent whereever there is water, providing an enormous amount of food for freshwater and marine ecosystems.

Genetic variation in bacterial populations cannot result from

a) transduction
b) transformation
c) conjugation
d) mutation
e) meiosis

A) light as an energy source and CO2 as a carbon source
B) light as an energy source and methane as a carbon source
C) N2 as an energy source and CO2 as a carbon source
D) CO2 as both an energy source and a carbon source
E) H2S as an energy source and CO2 as a carbon source

Gram-positive bacteria consist of free-living species that help decompose the organic matter in soil.

Plantlike photosynthesis that releases O2 occurs in

A) cyanobacteria
B) actinomycetes
C) chemoautotrophic bacteria
D) chlamydias
E) archaea


The green sulfur bacteria are a family of obligately anaerobic photoautotrophic bacteria most closely related to the distant Bacteroidetes. They are non-motile with the exception of Chloroherpeton thalassium, which may glide. They come in sphere, rods, and spiral forms. Photosynthesis is achieved using bacteriochlorophyll (BChl) c, d, or e, in addition to BChl a and chlorophyll a, in chlorosomes attached to the membrane. The electron transport chain (ETC) of green sulfur bacteria uses the reaction centre bacteriochlorophyll pair, P840. When light is absorbed by the reaction center, P840 enters an excited state with a large negative reduction potential, and so readily donates the electron to bacteriochlorophyll 663 which passes it on down the electron chain. The electron is transferred through a series of electron carriers and complexes until it either returns to P840 or is used to reduce NAD+. If the electron leaves the chain to reduce NAD+, P840 must be reduced for the ETC to function again. The green sulfur bacterias&rsquo small dependence on organic molecule transporters and transcription factors indicates that these organisms are adapted to a narrow range of energy-limited conditions, and fit into an ecology shared with the simpler cyanobacteria,

Figure: Green d winogradsky: A column containing green sulfur bacteria which uses anoxygenic photosynthesis.

The structural and molecular biology of type I galactosemia: Enzymology of galactose 1-phosphate uridylyltransferase. 2011, 63, 694-700. Figure 3. Mechanism .

Secondary lysosomes digest extracellular material of which is engulfed into the cell by a process called endocytosis. A phagocytic vesicle is pinched off fro.

• Elevated lactate leads to tissue hypoxia, hypoperfusion, and possible damage. (Wikipedia, 2013) CITRIC ACID CYCLE • 3 types of molecules can feed into .

DA is synthesized in the brain, kidneys, plants, and most multicellular animals. The first step in the biosynthesis of Dopamine uses the enzyme Tyrosine Hydr.

The objective of this lab was to isolate and identify an unknown Gram positive and Gram negative bacteria through the use of various microbiological techniqu.

Salivary amylase works to hydrolyze the – 1, 4 –glycosidic linkages between the maltose and glucose monosaccharides in starch (Tracey et al. 2016).

NADH and FADH2 can be used in the electron transport chain to create ATP by oxidative phosphorylation. During oxidative phosphorylation which takes place in .

Actually biosynthesis is an enzyme-catalyzed process in which substrates are converted into complex compounds. 1. Biosynthesis of fatty acids: Synthesis of .

Figure 3: Two metal ions catalysis mechanism of E. coli alkaline phosphatase (9). Zn(II) ions and essential amino acids are shown while Mg(II) ion is not dis.

Gold electrodes were prepared after cleaning with H2SO4 and H2O2. Glucose oxidase and laccase were immobilized on the GO/Co/chitosan modified electrodes in a.

Endotoxins from Cyanobacteria and Gram-negative Bacteria as the Cause of an Acute Influenza-like Reaction after Inhalation of Aerosols

Endotoxins (lipopolysaccharides) in aerosols, originating from cyanobacteria and gram-negative bacteria, were the likely etiological agent behind outbreaks of a transient, flu-like syndrome, described from four Scandinavian towns and Harare, Zimbabwe. The syndrome with fever, malaise, muscle pains, tightness of the chest and respiratory-tract symptoms, also known as toxic pneumonitis, occurred 1.5–6 hours after taking a bath or shower. The outbreaks were associated with mass developments of cyanobacteria in the drinking water reservoirs. Cyanobacterial cells and elevated levels of endotoxins were detected in the Harare tap water when human subjects reported symptoms. In a field study of 21 water bodies, the concentrations of endotoxins were much higher in water dominated by cyanobacteria, compared to water with dominance of eukaryotic algae. This observation may partially be explained by the fact that cyanobacteria possess endotoxins and partially by our findings that endotoxin-possessing bacteria inhabit the mucilage of several mass developing cyanobacterial taxa.

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