| Specialized structures |
Filamentous organisms
that divide exclusively by binary fission and in one
plane. The trichomes are straight to loosely sinuous near
apices; flexible or semirigid. Transverse septa are
generally visible under light microscopy Constrictions
may or may not occur at cross-walls, but the total
indentation never exceeds one eighth of the trichome
diameter. Generally, the transverse septum (cross-wall)
is thinner than the longitudinal wall. During fission the
cytoplasmic membrane invaginates, with a thinner
peptidoglycan layer separating the new membranes of the
daughter cells (This characteristic applies to the genera
Spirulina, Arthrospira, and Lyngbya in addition to
Oscillatoria. Cells may be much shorter than broad
(appearing as stacked disks) to a few times longer than
broad (The trichome diameters range from about 1 um to
occasionally > 100 um. Invariably in broader trichomes
(>15 um in diameter) the cells are shorter than long.
The trichome is usually motile and rotates in either a
left- or right-handed manner with respect to the
direction of movement. If terminal regions are not in
contact with substrate, the free end may appear to
oscillate as the trichome rotates, particularly if the
free end is curved. Rates of movement range from < 1
to about 11 um/s (Halfen and Castenholz 1971). Usually,
sheaths are nearly invisible, gossamer tubes that are
shed as flattened trails when the trichome moves on solid
substrates. Occasionally, more visible sheath may build
up on some trichomes, particularly during periods of
immobility in liquid culture (Chang, 1977). Trichomes are
solitary, but if clustered or in fabriclike mats they are
not surrounded by a morphologically distinct common
sheath. Copious amounts of gellike matter, however, may
be produced, particularly in liquid culture. |