Natural Relationships Among Sulfate-reducing Eubacteria

Phylogenetic relationships among 20 nonsporeforming and two endospore-forming species of sulfate-reducing eubacteria were inferred from comparative 16S rRNA sequencing. All genera of mesophilic sulfate-reducing eubacteria except the new genus Desulfomicrobium and the gliding Desulfonema species were included. The sporeforming species Desulfotomaculum ruminis and Desulfotomaculum orientis were found to be gram-positive organisms sharing 83% 16S rRNA sequence similarity, indicating that this genus is diverse. The gram-negative nonsporeforming species could be divided into seven natural groups: group 1, Desulfovibrio desulfuricans and other species of this genus that do not degrade fatty acids (this group also included "Desulfomonas" pigra); group 2, the fatty acid-degrading "Desulfovibrio" sapovorans; group 3, Desulfobulbus species; group 4, Desulfobacter species; group 5, Desulfobacterium species and "Desulfococcus" niacini; group 6, Desulfococcus multivorans and Desulfosarcina variabilis; and group 7, the fatty acid-oxidizing "Desulfovibrio" baarsii. (The quotation marks are used to indicate the need for taxonomic revision.) Groups 1 to 3 are incomplete oxidizers that form acetate as an end product; groups 4 to 7 are complete oxidizers. The data were consistent with and refined relationships previously inferred by oligonucleotide catalogs of 16S rRNA. Although the determined relationships are generally consistent with the existing classification based on physiology and other characteristics, the need for some taxonomic revision is indicated.