S54: A multipronged approach ranging from pure cultures to microbial communities to determine the mechanism of mercury methylation

In microbial transformation and genetic studies, we are attempting to discern the organisms and genes responsible for methylmercury (MeHg) generation. Using D. desulfuricans ND132, we sequenced the genome and are constructing a transposon library to identify the methylating gene(s). In ecological studies, MeHg generating microbial communities were examined using a functional gene array (FGA) and phylogenetically via 454 amplification and sequencing of the V4 region of 16S genes. Analysis of 59 samples revealed pronounced phylogenetic and functional differences that appear to be related to seasonal trends. Geochemical principal component analysis showed that one area was substantially different due to the presence of U(VI) and nitrate, and this was reflected in the microbial community. Virtually all of the microbial communities in the other five sites trended towards dissolved Hg. Further, a correlation of the 454 data with geochemistry at the phylum and genus level showed that some Hg methylating bacteria such as Geobacter spp. do not correlate with Hg or MeHg. However, the Delta- and Epsilon- Proteobacteria as well as Verrucomicrobia all trended towards dissolved Hg, and Desulfobulbus spp. strongly trended towards MeHg. This is significant in that Desulfobulbus proprionicus is a known Hg methylator. Current ecological efforts include enrichment and isolation of methylating bacteria from these sites as well as six metagenomic, metatranscriptomic, and metaproteomic analyses from three background, Hg(II) contaminated, and MeHg generating sites so as to more comprehensively ascertain the genes and gene products that are differentially abundant and expressed in active MeHg generating ecosystems.