| Staining |
Gram-negative |
| Morphology |
Colourless cells, about
1.50 um in diameter and about 2-10 um in length, occur in
filaments with diameters of from about 1 to > 50 um.
Organisms may exist as single cells or in filaments
containing up to 50 or more cells. Cells in filaments are
cylindrical and are longer than they are wide in the
thinner strains (about < 7 um in diameter). In wider
strains (about > 7 um in diameter), cells are usually
disk-shaped and typically are wider than they are long.
Filaments occur singly or in cottony masses in which each
filament retains its individuality |
| Motility |
Hormogonia and filaments
are motile by gliding; no motility organelles are known.
Gliding is relatively rapid (1-8 um s-1) and is often
accompanied by flexing and bending of the filaments. |
| Specialized structures |
Reproduction is by
transverse binary fission of cells within filaments;
divisions are made by septation, in which the
peptidoglycan and cytoplasmic membranes close like the
iris of a diaphragm. Filament dispersion is via
sacrificial cell death (necridial cells) and filament
breakage or via simple disintegration. With some strains,
the disintegration of filaments occurs until mostly
single or double cell units (hormogonia) exist; a
hormogonium then may grow to become a filament. Cells
contain inclusions of sulfur when they are grown in the
presence of hydrogen sulfide and, with some strains,
thiosulfate. Intracellular inclusions of
poly-B-hydroxybutyric acid (PHB) or polyphosphate may be
present. Resting stages are not known. Attachment
holdfasts or sheaths are not present. Capsules are not
formed, but filaments usually produce a slime matrix. |
| Tropism |
Chemoorganotrophic and
facultatively autotrophic. Some strains may also grow
mixotrophically. Only a marine strain has thus far been
proven to grow autotrophically |
| Oxygen |
Aerobic or
microaerophilic. Metabolism is respiratory with molecular
oxygen used as the terminal electron acceptor. Internally
stored sulfur may also serve as an electron acceptor for
short term maintenance in the absence of oxygen.
Anaerobic growth is not known. Nitrate, nitrite or
sulfate does not substitute as the terminal electron
acceptor for anaerobic growth in strains thus far
studied. |
| pH |
|
| Temperature |
Growth may occur between
0 and 40`C. Thermophilic strains have not been
characterized, although some beggiatoas have been
observed in high temperature runoffs associated with
thermal springs. |
| Requirements |
Growth factors are not
required by most strains; some strains may require
vitamin B12 H2S or thiosulfate may be used as the
electron donor for chemolithotrophic metabolism
Dinitrogen is fixed by a variety of strains. Nitrate,
nitrite, ammonium, dinitrogen or certain amino acids are
used as sole nitrogen source. |
| Products |
Acetate is oxidized to
CO2 by all freshwater strains tested. Several C2, C3, and
C4 organic acids and, sometimes, their amino acid
equivalents are utilized as sole carbon and energy
sources for hetero-trophic growth |
| Enzymes |
. Oxidase-positive,
catalase-negative Gelatin and starch are not hydrolyzed |
| Unique
features |
Beggiatoas are gradient
organisms existing in horizontal layers in sedimentsat
the interface between the underlying anoxic
sulfide-liberating zone and the overlying oxic zone. |