DIVERSITY OF SULFATE‐REDUCING GENES (dsrAB) IN SEDIMENTS FROM PUGET SOUND

Abstract

The aims of this study were to characterize the population structure and diversity of sulfate‐reducing bacteria (SRB) from three distinct sites at Puget Sound, and relate the biogeochemical properties of the sediments to the sulfate‐reducer communities. The population composition and diversity of sulfate‐reducing bacteria carrying dsrAB genes from surface Puget Sound sediments was investigated using a polymerase chain reaction‐based cloning approach. Sediment cores were collected from three different locations: Carr Inlet (C1A), Shallow Bud Inlet (S1A), and Turning Basin (T1A). A total of 498 dsrAB clones were sequenced from the three sites. Ecological indices indicated that T1A had the highest diversity and evenness values and C1A had the lowest. Correlations were also found between diversity indices and geochemical parameters. The diversity of the SRB decreased with decreasing carbon concentrations and sulfate reduction rates, and increasing levels of oxygen. A phylogenetic comparison revealed that the majority of the dsrAB sequences were associated with the delta‐proteobacterial phylotypes Desulfonema, Desulfococcus and Desulfosarcina, suggesting that complete oxidizers with high substrate versatility dominate in the sediments. The environmental conditions and energy sources available in the sediments may have dictated microbial community structure and diversity of SRBs. Distinctive community structures of SRBs in Puget Sound sediments were found to vary at different sites with different redox profiles. The dominance of the Desulfobacteraceae‐like sequences may be due to the presence of a diverse spectrum of substrates in the sediments. This study represents one of the first efforts to characterize the population of sulfate‐reducing microbes in the oxygenated regions of Puget Sound sediments. The phylogenetic identification of dsrAB genes in the sediment samples allows the composition of sulfate‐reducing prokaryotic communities to be inferred, and working hypotheses about their likely carbon substrates to be formed.