Cyanobacteria

The only form of cellular movement in cyanobacteria is gliding locomotion, it is widespread but not universal. 

Cyanobacteria belong to the group of Gram-negative bacteria, as defined now by the fine structure and molecular composition of the cell wall. 

The upper temperature limit for the growth of phototrophic eukaryotes is 55-60°C. Certain cyanobacteria are thermophiles, with temperature maxima as high as 75°C. As a result, they constitute the dominant or almost the exclusive photosynthetic population of hot springs. Thermotolerance seems to be the major factor which makes cyanobacteria the most important agents of photosynthesis in deserts. They develop as a subsurface layer in desert rocks, in microfissures where water is trapped by condensation at night. 

Many cyanobacteria can fix atmospheric nitrogen and dominate the microbial phototrophic population in environments where the supply of combined nitrogen is limiting. Until recently, heterocystous cyanobacteria were the only cyanobacteria known to fix nitrogen. Non-heterocystous cyanobacteria (e.g., Gloeothece, Plectonema, etc.) able to synthesize nitrogenase have since been recognized. 

Cyanobacteria are very widely distributed microorganisms. They can be found in hot sulphur springs at temperatures as high as 70°C and in all soils and most aquatic environments, particularly in the tropics. Some planktonic cyanobacteria are buoyant and under calm conditions they float to the surface of lakes and ponds forming the so-called water blooms. This buoy-ance is associated with the presence in the cells of gas vacuoles. However, cyanobacteria are not very abundant in oceanic plankton. The symbiotic species Richelia (Fig. 4.8) occurs in the diatom Rhizosolenia. Symbiotic relationships of cyanobacteria are quite common in algae, ferns, liverworts, gymnosperms and angiosperms. 

---

Free-living bacteria are, however, used as the source of the enzyme nitrogenase, responsible for N2 fixation (1,4,26,80), for research purposes because these ate easier to culture. The enzyme is virtually identical to that from the agriculturally important thizobia. These free-living N2-fixets can be simply classified into aerobes, anaerobes, facultative anaerobes, photosynthetic bacteria, and cyanobacteria. 

Public concern about the abundance of algae, and of the toxic cyanobacteria in particular, was raised by events in the UK in the summer of 1989 which involved the deaths of dogs and sheep at Rutland Water, Leicestershire, and the acute... 

In this way, the near-linear chlorophyll-phosphorus relationship in lakes depends upon the outcome of a large number of interactive processes occurring in each one of the component systems in the model. One of the most intriguing aspects of those components is that the chlorophyll models do not need to take account of the species composition of the phytoplankton in which chlorophyll is a constituent. The development of blooms of potentially toxic cyanobacteria is associated with eutrophication and phosphorus concentration, yet it is not apparent that the yield of cyanobacterial biomass requires any more mass-specific contribution from phosphorus. The explanation for this paradox is not well understood, but it is extremely important to understand that it is a matter of dynamics. The bloom-forming cyanobacteria are among the slowest-growing and most light-sensitive members of the phytoplankton. ... 

Physical controls are generally only applicable in lakes. The infinence of river morphology on eutrophication is not sufficiently well understood to be used effectively. The exception to this would be the short-term use of high flow to reduce the retention time to levels which limit growth rates of nuisance species such as cyanobacteria. 

S. -Z. Yu, in Toxic Cyanobacteria Current Status of Research and Management, proeeedings of an... 

Lipopolysaccharide (LPS) endotoxins are characteristic Gram-negative outer-cell components which are produced by many cyanobacteria. Although LPS have been characterized and found to be toxic to laboratory animals after isolation from cyanobacteria, their toxicity to rodents is less potent than the endotoxins of enteric pathogens such as Salmonella Typical symptoms of animals suffering from LPS intoxication include vomiting, diarrhoea, weakness and death after hours rather than minutes. 

In vitro cytotoxicity assays using isolated cells have been applied intermittently to cyanobacterial toxicity testing over several years." Cells investigated for suitability in cyanobacterial toxin assays include primary liver cells (hepatocytes) isolated from rodents and fish, established permanent mammalian cell lines, including hepatocytes, fibroblasts and cancerous cells, and erythrocytes. Earlier work suggested that extracts from toxic cyanobacteria disrupted cells of established lines and erythrocytes," but studies with purified microcystins revealed no alterations in structure or ion transport in fibroblasts or erythrocytes,... 

In addition to detection of toxicity in samples containing cyanobacteria and/or their toxins (i.e. screening), quantification and identification of the toxins present are necessary on occasions. Physicochemical methods of toxin analysis fulfil both these roles, often requiring a comparison of the test sample with purified... 

A powerful tool now employed is that of diode array detection (DAD). This function allows peaks detected by UV to be scanned, and provides a spectral profile for each suspected microcystin. Microcystins have characteristic absorption profiles in the wavelength range 200-300 nm, and these can be used as an indication of identity without the concomitant use of purified microcystin standards for all variants. A HPLC-DAD analytical method has also been devised for measurement of intracellular and extracellular microcystins in water samples containing cyanobacteria. This method involves filtration of the cyanobacteria from the water sample. The cyanobacterial cells present on the filter are extracted with methanol and analysed by HPLC. The filtered water is subjected to solid-phase clean-up using C g cartridges, before elution with methanol and then HPLC analysis. 

The ability to identify and quantify cyanobacterial toxins in animal and human clinical material following (suspected) intoxications or illnesses associated with contact with toxic cyanobacteria is an increasing requirement. The recoveries of anatoxin-a from animal stomach material and of microcystins from sheep rumen contents are relatively straightforward. However, the recovery of microcystin from liver and tissue samples cannot be expected to be complete without the application of proteolytic digestion and extraction procedures. This is likely because microcystins bind covalently to a cysteine residue in protein phosphatase. Unless an effective procedure is applied for the extraction of covalently bound microcystins (and nodiilarins), then a negative result in analysis cannot be taken to indicate the absence of toxins in clinical specimens. Furthermore, any positive result may be an underestimate of the true amount of microcystin in the material and would only represent free toxin, not bound to the protein phosphatases. Optimized procedures for the extraction of bound microcystins and nodiilarins from organ and tissue samples are needed. 

T. Kuiper-Goodman, S. Gupta, H. Combley and B. H. Thomas, in Toxic Cyanobacteria Current... 

Not all cyanobacterial blooms and scums contain detectable levels of toxins. Indeed, the incidence of toxicity detection by mouse bioassay, and toxin detection by HPLC among environmental samples, ranges from about 40% to However, in view of this high occurrence, it is the policy of regulatory authorities and water supply operators in some countries to assume that blooms of cyanobacteria are toxic until tested and found to be otherwise. In the absence of available analytical facilities or expertise or for logistical reasons, this precautionary principle should be regarded as sensible and prudent. 

Akinete Thick-walled resting cell of cyanobacteria and algae. 

Prokaryotic cells have only a single membrane, the plasma membrane or cell membrane. Because they have no other membranes, prokaryotic cells contain no nucleus or organelles. Nevertheless, they possess a distinct nuclear area where a single circular chromosome is localized, and some have an internal membranous structure called a mesosome that is derived from and continuous with the cell membrane. Reactions of cellular respiration are localized on these membranes. In photosynthetic prokaryotes such as the cyanobacteria,... 

Photoautotrophs CO2 Light H2O, H2S, S, other inorganic compounds Green plants, algae, cyanobacteria, photosynthetic bacteria... 

Two classes of aldolase enzymes are found in nature. Animal tissues produce a Class I aldolase, characterized by the formation of a covalent Schiff base intermediate between an active-site lysine and the carbonyl group of the substrate. Class I aldolases do not require a divalent metal ion (and thus are not inhibited by EDTA) but are inhibited by sodium borohydride, NaBH4, in the presence of substrate (see A Deeper Look, page 622). Class II aldolases are produced mainly in bacteria and fungi and are not inhibited by borohydride, but do contain an active-site metal (normally zinc, Zn ) and are inhibited by EDTA. Cyanobacteria and some other simple organisms possess both classes of aldolase. 

In cyanobacteria and the eukaryotic photosynthetic cells of algae and higher plants, HgA is HgO, as implied earlier, and 2 A is O,. The accumulation of O, to constitute 20% of the earth s atmosphere is the direct result of eons of global oxygenic photosynthesis. 

All photosynthetic cells contain some form of photosystem. Photosynthetic bacteria, unlike cyanobacteria and eukaryotic phototrophs, have only one photosystem. Interestingly, bacterial photosystems resemble eukaryotic PSII more than PSI, even though photosynthetic bacteria lack Og-evolving capacity. 

---