PHYLOGENETIC CHARACTERIZATION OF BACTERIA IN THE SUBSURFACE MICROBIALCULTURE COLLECTION

The Subsurface Microbial Culture Collection (SMCC) was established by the U.S. Dept. of Energy (DOE) and contains nearly 10,000 strains of m icroorganisms (mostly bacteria) isolated from terrestrial subsurface e nvironments. Selected groups of bacterial isolates from three sample s ites situated above geochemically and hydrologically different subsurf ace environments have been characterized by phylogenetic analysis of 1 6S ribosomal RNA (rRNA) gene nucleotide sequences. Among these isolate s were members of six major phylogenetic groups of bacteria: the high- G+C and low-G+C Gram-positive bacteria; the alpha-, beta-, and gamma-s ubdivisions of the Proteobacteria; and the Flexibacter/Cytophaga/Bacte roides group. A small number of the SMCC strains may be members of new bacterial genera, but most of them could be placed with reasonable co nfidence into more than 35 previously described genera. The majority o f the Gram-positive isolates were species of Arthrobacter, Bacillus, o r Streptococcus, whereas Acinetobacter, Comamonas, Pseudomonas, Sphing omonas, and Variovorax were among the most frequently encountered Gram -negative genera. A high proportion of the strains were placed in fewe r than 10 genera, implying that there is substantial duplication withi n the SMCC at the genus level. When groups of isolates assigned to Aci netobacter, Arthrobacter, or Sphingomonas were analyzed in more detail , however, it was found that each group consisted of subgroups of stra ins that probably differed at the species level. Restriction endonucle ase analysis (applied to the strains from one sample site) indicated t hat additional diversity was present at the strain level. Most of the SMCC isolates assigned to some genera (e.g., Acinetobacter) were very closely related to previously described species in those genera, but m ost of the isolates assigned to other genera (e.g., Arthrobacter and S phingomonas) appeared (or were shown) to be new species, thereby indic ating that a reasonable amount of novelty is present within the SMCC a t the species level.