Beggiatoa in microbial mats at hydrocarbon vents in the Gulf of Mexico and Warm Mineral Springs, Florida

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Microbial mats were collected from a variety of sites near hydrocarbon vents along the slope in the northern Gulf of Mexico and, for comparison, from Warm Mineral Springs, Florida, USA. A predominant microorganism in each of the mats was the giant bacterium, Beggiatoa. Diameters of the bacterial filaments ranged from about 6 μm to approximately 200 μm. The latter organisms are the largest prokaryotic organisms yet found. All filaments over about 10 μm in diameter contained a large central vacuole, producing a cell with the cytoplasm as a cylindrical tube underlying the cytoplasmic membrane. Sulfur globules were confined to this peripheral layer. Push cores often contained pyrite tubules whose appearance is suggestive of a Beggiatoa origin. Determinations of δ13C in Beggiatoa mats from vents along the Louisiana slope yielded values in the range of -26.6 to -27.9‰ (PDB), suggesting an unusually high degree of isotope fractionation (-24.9‰) relative to the carbon source in the ambient seawater, which is typical of sulfur-oxidizing chemoautotrophs. The presence of SO (elemental sulfur) within cells of Beggiatoa resulting from oxidation of H2S supports the importance of bacterial sulfate reduction processes in the underlying vents for the sustenance of the Beggiatoa mats. © 1994 Springer-Verlag.

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Geo-Marine Letters

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