The effect of an induced benzene plume on microbial communities in a groundwater aquifer

This study investigated the degradation of a benzene plume by indigenous microbial communities in sediments and groundwater from the SIReN (Site for Innovative Research in Natural Attenuation). A sandbox mesocosm system and microcosms were inoculated with SIReN sediments/groundwater and spiked separately with plume (starting concentration of 1000 mg/l-1) and various concentrations of benzene (5 ? 500 mg/l-1). Benzene plume was degraded almost at the point of entry, while in aerobic microcosms benzene was degraded to varying degrees by day 6 compared to killed controls. DGGE analysis of 16S rRNA gene (rDNA) allowed the detection of species closely related to Rhodoferax ferrireducens (95% similarity) and Dechloromonas aromatica RCB (99% similarity). Other organisms detected were closely related to Methylotenera mobilis strain JLW8 (92 ? 96% similarity); Nitrosomonas halophila strain Nm 1 (97% similarity); Insolitispirillum peregrinum subsp. integrum strain LMG 5407 (99% similarity); and Lactococcus lactis strain SWU15983 (97% similarity). Our results demonstrated that benzene contamination had a profound impact on in situ microbial community structure and composition. Furthermore, the abundance of organisms closely related to methylotrophic bacteria may be indicative of a more ?active? role in bioremediation for this group than previously known. Results from this study add to available information on the identity of benzene-degrading taxa that may be useful for the bioremediation of hydrocarbon-contaminated aquifers under microaerophilic conditions.