Beggiatoa

Abstract

Beg.gi.a.to' a . M.L. fem. n. Beggiatoa a genus of bacteria; named in remembrance of F.S. Beggiato, a physician of Vicenza, (g.b. 1807), who authored the Delle Terme Euganea . Proteobacteria / Gammaproteobacteria / Thiotrichales / Thiotrichaceae / Beggiatoa Colorless cells, ~1.0–200 × 2.0–10.0 μm, occurring in filaments 5.0–10 cm in length . Filaments usually have a consistent width over the entire length. Freshwater strains mostly, if not universally, possess filament diameters less than 5.0 µm, whereas marine beggiatoas with filament diameters ranging from 1.0 to 200 µm have been observed microscopically. No strain wider than 5 µm has been isolated in axenic culture from any source. The filaments may contain up to 100 or more cells, and in rare cases, up to several thousand. Cells in filaments are cylindrical and are longer than they are wide in the thinner strains (i.e., those less than ~5 µm in diameter). In wider strains (i.e., those greater than ~7 µm in diameter), cells are usually disk‐shaped and typically are wider than they are long. Filaments occur singly, in sheets of cottony masses on sediment surfaces, or in mats in which each filament retains its individuality. Reproduction is by transverse binary fission of cells within filaments; division occurs 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), filament breakage, or simple disintegration. In some strains, the disintegration of filaments occurs until mostly single or double cell units (hormogonia) exist; a hormogonium then can grow to become a filament. Cells contain inclusions of sulfur when grown in the presence of H 2 S and, for some strains, thiosulfate . Intracellular inclusions of poly‐β‐hydroxybutyrate or polyphosphate may be present, particularly in freshwater strains. Marine or brackish water strains having a filament diameter of >10 μm contain a large (~80% of the cell volume), central liquid vacuole that contains concentrated nitrate . Resting stages are not known. Attachment holdfasts or sheaths are not present . Capsules are not formed, but filaments usually produce a slime matrix. Gram negative. Filaments and hormogonia have gliding motility . No motility organelles are known. Aerobic or microaerophilic, having a strictly respiratory type of metabolism , with oxygen and, in some instance, nitrate as the terminal electron acceptor. Anaerobic growth is not proven with pure cultures, but may occur with nitrate as the terminal electron acceptor for some strains studied in nature. Internally stored sulfur may also serve as an electron acceptor by freshwater strains for short‐term maintenance in the absence of oxygen. Sulfate does not substitute as the terminal electron acceptor for anaerobic growth in strains thus far studied. Chemoorganotrophic (freshwater strains), and either facultatively or constitutively chemolithoautotrophic (marine strains) . H 2 S or thiosulfate may be used as the electron donor for chemolithotrophic metabolism . Acetate is oxidized to CO 2 by all freshwater strains tested thus far. Several C 2 , C 3 , and C 4 organic acids and, sometimes, their amino acid equivalents are utilized as sole carbon and energy sources for heterotrophic growth . Growth factors are not required by most strains, although some strains may require vitamin B 12 . Gelatin and starch are not hydrolyzed. N 2 is fixed by all freshwater and marine strains tested thus far . Nitrate, nitrite, ammonium, N 2 , or certain amino acids may be used as the sole nitrogen source. Oxidase positive. Catalase negative . Freshwater, estuarine, and marine strains are known. Beggiatoas are inherently gradient organisms, growing in horizontal layers in sediments at the interface between the underlying anoxic sulfide‐liberating zone and the overlying oxic zone . Growth can occur in the range of 0–40°C. Obligately thermophilic strains have not been characterized, although some beggiatoas have been observed in high temperature runoffs associated with thermal springs, or in mats adjacent to thermal vents in the ocean floor. The mol % G + C of the DNA is : 35–39. Type species : Beggiatoa alba (Vaucher 1803) Trevisan 1842, 56.