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PseudanabaenaRANK: GenusTAXONOMY: Bacteria -> Terrabacteria group -> Cyanobacteria/Melainabacteria group -> Cyanobacteria -> Oscillatoriophycideae -> Oscillatoriales -> Pseudanabaena OVERVIEW: Trichomes that divide exclusively by binary fission in one plane and have conspicuous constrictions at the crosswalls that may exceed half the cell diameter (Figure 1). In some strains, the total constriction is less but is still more than 1/8 the cell diameter (Guglielmi and Cohen-Bazire, 1984a). Cells are longer than broad to isodiametric and are often barrel-shaped. Trichomes of strains characterized in culture range from ∼1 to 3 µm in diameter. The formation of the transverse septum involves a partial centripetal ingrowth of all wall layers. In some cases, the remaining connection appears quite narrow, as if the cells were strung as beads. The structural (peptidoglycan) layer of the cross-wall is 3–6 times thicker than the layer surrounding the rest of the cell (Guglielmi and Cohen-Bazire, 1984a) (Figure 2). Another characteristic observed through T.E.M. is the consistency of peripheral thylakoids, parallel to the cell walls. Near the cross-walls, the continuity of thylakoids may be interrupted by gas vesicle clusters. The trichomes are usually straight and, depending on the morphotype, may be quite short (consisting of less than 3 to ∼10 cells) or may be longer (>10 cells). Reproduction by intercellular trichome breakage. Single detached cells are frequently found in cultured populations and may be confused with unicellular cyanobacteria (Castenholz, unpublished). Gliding motility, probably without rotation, occurs at rates usually <1 µm/s. Gliding motility has been lost in a few cultured strains (Guglielmi and Cohen-Bazire, 1984a). |