Physiology and evolutionary relationships of novel vacuolate sulfur bacteria from hydrothermal vents and cold seeps.

摘要

Conspicuous, vacuolate, filamentous sulfur bacteria occur at shallow hydrothermal vents near White Point, California, and at deep-sea vents at Escanaba Trough and Juan de Fuca off the coast of Washington. These cells attach in dense chains to diverse substrates and extend one to several cm into the surrounding environment which is alternately sulfidic and oxic. Native filaments collected from these locations possess novel morphological and physiological properties compared to all other vacuolate bacteria characterized to date. Attached filaments, ranging in diameter from 4 mum to 100+ mum, are composed of cylindrical shaped cells containing a thin annulus of cytoplasm surrounding a large central vacuole. Separate, nearly full-length, 16S rRNA gene sequences obtained from populations at the three vent locations were confirmed by fluorescent in situ hybridization (FISH) to derive from the target bacteria. Phylogenetic analysis indicates that these organisms form a tight cluster within the larger monophyletic group that includes all previously described vacuolate sulfur bacteria. However, unlike previously described vacuolate bacteria, these organisms do not store internal nitrate.; Large spherical sulfur bacteria, 180 to 375 mum in diameter, were discovered in surface sediments collected from sulfidic seeps in the Gulf of Mexico. These abundant bacteria were characterized by a thin 'shell' of cytoplasm that surrounded a large central vacuole containing high concentrations of nitrate (460 mM). Approximately 800 base pairs of 16S rRNA gene sequence data, linked to this bacterium by FISH, showed 99% identity with the sequence for Thiomargarita namibiensis. Unlike T. namibiensis , in which cells form a chain within a common sheath, the Gulf of Mexico strain occurred as single cells or 2-, 4- and 8-cell clusters. The latter clusters result from division in two or three orthogonal planes, which has not been observed in T. namibiensis. In sediment cores maintained at 4°C the bacterium remained viable for up to 2 years with each cell undergoing one to three reductive divisions during that period. This unique form of division is possibly a response to diminishing fluxes of hydrogen sulfide.