Phylogenetic identification and substrate uptake patterns of sulfate-reducing bacteria by MAR-FISH

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We simultaneously determined the phylogenetic identification and substrate uptake patterns of sulfate-reducing bacteria (SRB) inhabiting a sewer biofilm with oxygen, nitrate, or sulfate as electron acceptors by combining microautoradiography and fluorescenct in situ hybridization (MAR-FISH) with family- and genus-specific 16S rRNA probes. The MAR-FISH analysis revealed that Desulfobulbus hybridized with probe 660 was a dominant SRB subgroup in this sewer biofilm, which accounted for 23% of total SRB. Approximately 9% and 27% of Desulfobulbus detected with probe 660 could take up [^<14>C]propionate with oxygen and nitrate as electron acceptor, respectively, which might explain the high abundance of this species in various oxic environments. Furthermore, more than 40% of Desulfobulbus incorporated acetate into cells under anoxic conditions. SRB were also numerically important members of H_2-utilizing and [^<14>C]CO_2-fixing microbial populations in this sewer biofiim, which roughly acccunted for 42% of total H_2-utilizing bacteria hybridized with probe EUB338. A comparative 16S rDNA analysis revealed that two SRB populations, related to the Desulfomicrobium hypogeium and the Desultfovibrio desulfuricans MB lineages, were found to be important H_2-utilizers in this biofilms. Substrate uptake characteristics of different phylogenetic SRB subgroups was compared with the characteristics described to date. These results provide further insight into the correlation between 16S rRNA phylogenetic diversity and physiological diversity of SRB populations inhabiting sewer biofilms.