Anaerobic Benzene Biodegradation Linked to the Growth of Highly Specific Bacterial Clades

Reliance on bioremediation to remove
benzene from anoxic environments
has proven risky for decades but for unknown reasons. Research has
revealed a strong link between anaerobic benzene biodegradation and
the enrichment of highly specific microbes, including Thermincola in the family Peptococcaceae and the deltaproteobacterial Candidate Sva0485 clade. Using aquifer
materials from Canadian Forces Base Borden, we compared five bioremediation
approaches in batch microcosms. Under conditions simulating natural
attenuation or sulfate biostimulation, benzene was not degraded after
1–2 years of incubation and no enrichment of known benzene-degrading
microbes occurred. In contrast, nitrate-amended microcosms reported
benzene biodegradation coincident with significant growth of Thermincola spp., along with a functional gene presumed
to catalyze anaerobic benzene carboxylation (abcA). Inoculation with 2.5% of a methanogenic benzene-degrading consortium
containing Sva0485 (Deltaproteobacteria ORM2) resulted in benzene biodegradation in the presence of sulfate
or under methanogenic conditions. The presence of other hydrocarbon
co-contaminants decreased the rates of benzene degradation by a factor
of 2 to 4. Tracking the abundance of the abcA gene
and 16S rRNA genes specific for benzene-degrading Thermincola and Sva0485 is recommended to monitor benzene bioremediation in
anoxic groundwater systems to further uncover growth-rate-limiting
conditions for these two intriguing phylotypes.