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Me.tha.no.bre.vi.bac' ter . M.L. neut. n. methanum methane; L. masc. adj. brevis short; M.L. masc. n. bacter equivalent of Gr. neut. n. bakterion rod, staff; M.L. masc. n. Methanobrevibacter short methane (‐producing) rod. Euryarchaeota / Methanobacteria / Methanobacteriales / Methanobacteriaceae / Methanobrevibacter Oval rods or cocci to short rods , usually occurring in pairs or chains; about 0.5–0.7 µm in width and 0.8–1.4 µm in length. Rarely, filaments are formed. Nonsporing, Gram‐positive. Cell walls are composed of pseudomurein . Nonmotile. Strict anaerobes. Optimum temperature, 37–40°C; maximum, ~45°C; minimum, ~30°C. The mol % G + C of the DNA is : 27.5–31.6. Type species : Methanobrevibacter ruminantium (Smith and Hungate 1958) Balch and Wolfe 1981, 216 (Effective publication: Balch and Wolfe in Balch, Fox, Magrum, Woese and Wolfe, 1979, 284) ( Methanobacterium ruminantium Smith and Hungate 1958, 717).

Apart from sharing the basic cellular features of other Bacteria , the cyanobacteria possess unique and diagnostic characteristics that will be briefly described here, but less extensively than in the 1989 edition of Bergey's Manual of Systematic Bacteriology . The cell wall in cyanobacteria is of a Gram‐negative type. Cell division in most unicellular and colonial cyanobacteria and some filamentous forms is by binary fission. Regarding cell exterior and motility, fimbriae (or pili) occur abundantly with diverse patterns in many cyanobacteria. Although not all thylakoids in cyanobacteria appear to be invaginations of the cytoplasmic membrane, there are orderly “attachment points” or “thylakoid centers” associated with the periphery of the cytoplasm or the cytoplasmic membrane. In the cytoplasm of cyanobacteria there are many other components and “inclusions”, most of which can be visualized readily using various preparative techniques for transmission electron microscopy. They include glycogen granules, cyanophycin granules, carboxysomes (polyhedral bodies), polyphosphate (volutin) granules, and gas vacuoles. Heterocysts, akinetes, and hormogonia are some of the specialized cells and differentiation in Cyanobacteria. The chief physiological/biochemical characteristic of cyanobacteria, distinguishing them from all other procaryotes, is the dual photosystem that allows the use of H 2 O as photoreductant with the consequent liberation of O 2 . Two courses for the delimitation of genera have been followed by cyanobacterial specialists: (a) to retain “small” genera or (b) to gather many species into fewer genera. Cyanobacteria / General Characteristics of the Cyanobacteria