Molecular Analysis of the Metabolic Rates of Discrete Subsurface Populations of Sulfate Reducers

Abstract

ABSTRACTElucidating thein situmetabolic activity of phylogenetically diverse populations of sulfate-reducing microorganisms that populate anoxic sedimentary environments is key to understanding subsurface ecology. Previous pure culture studies have demonstrated that the transcript abundance of dissimilatory (bi)sulfite reductase genes is correlated with the sulfate-reducing activity of individual cells. To evaluate whether expression of these genes was diagnostic for subsurface communities, dissimilatory (bi)sulfite reductase gene transcript abundance in phylogenetically distinct sulfate-reducing populations was quantified during a field experiment in which acetate was added to uranium-contaminated groundwater. Analysis ofdsrABsequences prior to the addition of acetate indicated thatDesulfobacteraceae,Desulfobulbaceae, andSyntrophaceae-related sulfate reducers were the most abundant. QuantifyingdsrBtranscripts of the individual populations suggested thatDesulfobacteraceaeinitially had higherdsrBtranscripts per cell thanDesulfobulbaceaeorSyntrophaceaepopulations and that the activity ofDesulfobacteraceaeincreased further when the metabolism of dissimilatory metal reducers competing for the added acetate declined. In contrast,dsrBtranscript abundance inDesulfobulbaceaeandSyntrophaceaeremained relatively constant, suggesting a lack of stimulation by added acetate. The indication of higher sulfate-reducing activity in theDesulfobacteraceaewas consistent with the finding thatDesulfobacteraceaebecame the predominant component of the sulfate-reducing community. Discontinuing acetate additions resulted in a decline indsrBtranscript abundance in theDesulfobacteraceae. These results suggest that monitoring transcripts of dissimilatory (bi)sulfite reductase genes in distinct populations of sulfate reducers can provide insight into the relative rates of metabolism of different components of the sulfate-reducing community and their ability to respond to environmental perturbations.