Culture-independent survey of microbial communities

The purpose of this study was to assess the diversity and qualitative relative abundance of bacteria and archaea in the sediment or water column of two ~80 deg C hot springs, GBS and SSW, in the US Great Basin. The samples for DNA extraction were coordinated with measurements of ammonia oxidation, denitrification, and dissimilatory nitrate reduction to ammonia (DNRA) rates, and the data was used to determine which microbial groups might be responsible for these processes. Analysis of the amplified 16S rRNA gene pyrotag sequences was done using the program PyroTagger. The sediment and water hosted distinct microbial communities. Close relatives of the autotrophic, thermophilic ammonia-oxidizing archaeon "Candidatus Nitrosocaldus yellowstonii" represented the single most abundant OTU (at the 97% sequence identity) in the sediment fraction, and are likely responsible for the observed ammonia oxidation rates. Groups potentially responsible for the high measured denitrification and DNRA rates was less clear, but could include Hydrogenobacter and Thermus spp. Most other prominent OTUs represented novel lineages (>86% sequence identity to 16S rRNA genes of cultured microorganisms). These data suggest that ammonia oxidation may be an important energy source driving microbial metabolism and primary production in some terrestrial geothermal environments