Molecular Mechanisms of Microbial Resistance to Unfavorable Environmental Conditions in Heavy Metal Bioremediation: Organic Solvents as Co-Contaminants in Groundwater

Sulfate-reducing bacteria (SRB) have been studied extensively for their potential in the bioremediation of heavy metals and radionuclides in groundwater and sediments. Hydrocarbons and solvents, as frequent environmental co-contaminants, have been reported to inhibit microbial activities and thereby pose a challenge to the success of bioremediation efforts. In order to understand the molecular mechanisms of microbial resistance to the presence of organic solvents, we studied the responses of Desulfovibrio vulgaris as a model SRB to its exposure to the organic solvent acetone. Genome-wide transcriptional profiling of D. vulgaris cultures following acetone (5% v/v) treatment at 30 and 60 min revealed that genes encoding potassium ion transporters and flagella structural subunits are among the most highly up-regulated transcripts. Molecular chaperones comprised another group of genes highly induced in the presence of acetone. Down-regulated genes spanned many gene functional role categories, particularly energy metabolism and the biosynthesis of protein and DNA, suggesting the disruption of normal cell growth and metabolism upon acetone exposure. Results from this study confirmed previous indications that organic solvents adversely affect microorganism by impairing cell membrane integrity and inactivating cellular proteins. Accordingly, this study shows that the mechanisms to protect SRB from the toxicity of organic solvents include the maintenance of proper protein functions, restoration of ionic balance, and increased cell mobility.