Sulfur-metabolizing Bacteria Research Articles

Growth of the facultative anaerobe Shewanella putrefaciens by elemental sulfur reduction.

The growth of bacteria by dissimilatory elemental sulfur reduction is generally associated with obligate anaerobes and thermophiles in particular. Here we describe the sulfur-dependent growth of the facultatively anaerobic mesophile Shewanella putrefaciens. Six of nine representative S. putrefaciens isolates from a variety of environments proved able to grow by sulfur reduction, and strain MR-1 was chosen for further study. Growth was monitored in a minimal medium (usually with 0.05% Casamino Acids added as a growth stimulant) containing 30 mM lactate and limiting concentrations of elemental sulfur. When mechanisms were provided for the removal of the metabolic end product, H2S, measurable growth was obtained at sulfur concentrations of from 2 to 30 mM. Initial doubling times were ca. 1.5 h and substrate independent over the range of sulfur concentrations tested. In the cultures with the highest sulfur concentrations, cell numbers increased by greater than 400-fold after 48 h, reaching a maximum density of 6.8 x 10(8) cells ml-1. Yields were determined as total cell carbon and ranged from 1.7 to 5.9 g of C mol of S(0) consumed-1 in the presence of the amino acid supplement and from 0.9 to 3.4 g of C mol of S(0-1) in its absence. Several lines of evidence indicate that cell-to-sulfur contact is not required for growth. Approaches for the culture of sulfur-metabolizing bacteria and potential ecological implications of sulfur reduction in Shewanella-like heterotrophs are discussed.

Evidence that eukaryotes and eocyte prokaryotes are immediate relatives

The phylogenetic origin of eukaryotes has been unclear because eukaryotic nuclear genes have diverged substantially from prokaryotic ones. The genes coding for elongation factor EF-1 alpha were compared among various organisms. The EF-1 alpha sequences of eukaryotes contained an 11-amino acid segment that was also found in eocytes (extremely thermophilic, sulfur-metabolizing bacteria) but that was absent in all other bacteria. The related (paralogous) genes encoding elongation factor EF-2 and initiation factor IF-2 also lacked the 11-amino acid insert. These data imply that the eocytes are the closest surviving relatives (sister taxon) of the eukaryotes.

Tracing origins with molecular sequences: metazoan and eukaryotic beginnings

Milestones in the evolution of the eukaryotic cell are being discovered through the analysis of molecular sequences. As sequence data become increasingly plentiful, our ability to reconstruct the most distant evolutionary branchings of evolutionary trees is limited only by the mathematics of phylogenetic reconstruction. Analysis of ribosomal RNAs agrees with traditional analyses of morphological and developmental characters that all multicellular animals probably arose from a common ancestor, but high-lights one of the major limitations of the various mathematical algorithms used. Refined methods of sequence analysis also suggest a previously unsuspected sister relationship between the eukaryotic nucleus and eocytes, a group of extremely thermophilic, sulfur-metabolizing bacteria, that questions the classical eukaryote/prokaryote division.

5'-Methylbenzimidazolyl-cobamides are the corrinoids from some sulfate-reducing and sulfur-metabolizing bacteria.

The sulfate-reducing bacteria Desulfobacterium autotrophicum, Desulfobulbus propionicus and Archaeoglobus fulgidus (VC-16) and the sulfur-metabolizing archaebacteria Desulfurolobus ambivalens and Thermoplasma acidophilum were found to contain considerable amounts of corrinoids, that were isolated and crystallized in their Co beta-cyano form. In three other sulfur-metabolizing archaebacteria, Thermoproteus neutrophilus, Pyrodictium occultum and Staphylothermus marinus significant amounts of corrinoids were not detected under the isolation methods used. The samples from the three sulfate-reducers were identified with Co alpha-[alpha-(5'-methylbenzimidazolyl)]-Co beta-cyanocobamide. This corrinoid was also obtained from a 5-methylbenzimidazole-supplemented Propionibacterium fermentation and was structurally characterized by ultraviolet/visible, CD, fast-atom-bombardment MS, 1H-and 13C-NMR spectroscopy. Also the major corrinoid from T. acidophilum was (tentatively) analyzed as a 5'-methylbenzimidazolyl-cobamide, whereas the main corrinoid from D. ambivalens was indicated to be vitamin B12 (a 5',6'-dimethylbenzimidazolyl-cobamide). The 5'-methylbenzimidazolylcobamides are found here as the common corrins of some sulfate-reducing and sulfur-metabolizing bacteria. The structural diversity due to the differing nucleotide bases of the corrins examined here and in methanogenic and acetogenic bacteria appears not to correlate to the biological function(s) of the corrins, but rather to be determined by biosynthetic properties of these organisms under natural growth conditions.