Diversity, abundance and activity of microbial communities associated with anoxia in a hypersaline lake, the Salton Sea, California

Anaerobic environments are globally widespread and are colonized by microbes whose metabolic activities drive many of Earth's geochemical cycles. In this work, patterns of abundance, community structure, phylogenetic diversity, and activity of Archaea and Bacteria were compared along gradients in subsurface sediments and the water column of the Salton Sea, California.;Quantitative PCR assays (qPCR) of subsurface sediments revealed Archaea to be dominant at all depths, whereas Bacteria and Crenarchaeota were less abundant and exhibited stronger responses to changes in carbon and salinity with depth. Bacterial community structure (based on T-RFLP) patterns were correlated with salinity, whereas archaeal community patterns were weakly correlated with carbon. Archaeal diversity (16S rRNA) revealed diverse communities of Euryarchaeota and Crenarchaeota, and many were affiliated with previously described marine groups. The abundance of these groups across all depths suggests that several putatively marine archaeal groups are adapted to elevated salinity (5.0--11.8%) and sulfidic conditions of Salton Sea sediments. Differential responses of archaeal and bacterial communities to geochemical patterns are consistent with the hypothesis that adaptations to energy stress and availability distinguish the ecologies of these domains.;Shifts in water column microbial communities were strongly correlated with sulfide gradients formed by wind-driven lake mixing events. Actinobacteria, gamma--Proteobacteria (purple sulfur bacteria), and Chlorobi (green sulfur bacteria) were more prevalent at stations with higher sulfide concentration, and Synechococcus was the most abundant lineage at most stations. Archaeal diversity was low, and sequences were affiliated with methylotrophic Methanohalophilus, Methanococcoides, Methanosarcinales, and Marine Benthic Group (MBG)-D sequences. Compositional differences detected between stations may reflect differential tolerances or utilization of sulfide and other reduced-sulfur compounds by the planktonic microbial community.;Rate measurements, porewater constituents, and H2 concentrations of subsurface sediments were used to calculate depth profiles of free energy yield for dissimilatory sulfate reduction and energy flux. Sulfate reduction was found to be energetically favorable at all depths. In support of predictions of species-energy theory, significant, positive relationships between SRR and energy flux and bacterial abundance/richness were found. Estimations of energy flux may provide a unique means by which to compare species richness patterns across microbial systems.