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.

In situfilamentous communities from the Ediacaran (approx. 563 Ma) of Brazil

“…The oriented populations also suggest the influence of slow bottom currents that did not disarticulate or detach the specimens from the substrate prior to fossilization. Given the absence of evidence for strong sediment reworking and/or storm deposits, the filament orientation agrees with the interpretation [20] of an upper slope setting dominated by millimetre-scale intercalation of siltstones and claystones. In rare cases, filament overlapping patterns can even allow for inference of the likely sequence of filament superposition prior to burial (figure 2d; electronic supplementary material, figure S8), and the presence of the same sequence of orientation in different individuals show that this was not a random disposition of a particular specimen (e.g.…”

“…Finally, the in situ preservation of the filaments from the IB allows a unique opportunity to understand aspects of their palaeoecology and perhaps even their preferred metabolic pathway. Their partially buried, mostly prostrate mode of life, but often with portions of the filaments stretching out from the sediment surface (figure 5), is remarkably similar to the ecology of modern, large filamentous Beggiatoaceae [19,20] (electronic supplementary material, figure S12). Indeed, large, filamentous SOB can colonize extensive seafloor areas in dysoxic settings, building large communities that live attached and/or partially buried in the substrate [69].…”

“…Modern LFSOB are ubiquitous in marine and freshwater environments where H 2 S and oxygen geochemical gradients are prevalent (e.g. environments at the interface of euxinic and oxic conditions; [19,20]). Yet, only a few studies have suggested the presence of sulfur-oxidizing bacteria (SOB) in the fossil record [21][22][23].…”

“…Yet, only a few studies have suggested the presence of sulfur-oxidizing bacteria (SOB) in the fossil record [21][22][23]. This is owing, in part, to their simple morphology and overall morphological similarities with cyanobacteria [19,24].…”