Microbial community response of an organohalide respiring enrichment culture to permanganate oxidation

While in situ chemical oxidation (ISCO) is often used to remediate tetrachloroethene (PCE) contaminated locations, very little is known about the influence of oxidation on organohalide respiration (OHR) activity and especially microbial community structure. Here, we investigate the impact of oxidation with permanganate on OHR rates, the abundance of organohalide respiring bacteria (OHRB) and reductive dehalogenase (rdh) genes using quantitative PCR, and microbial community composition and dynamics based on sequencing of partial 16S rRNA gene fragments. A PCE degrading enrichment culture was treated with multiple rounds of low (25 µmol), medium (50 µmol), or high (100 µmol) permanganate doses, or no oxidant treatment (biotic control). Results indicate that under mild permanganate treatments (25 µmol or 50 µmol), chemical oxidation stimulated biodegradation leading to higher OHR rates and enrichment of a number of OHRB and rdh genes, as compared to the biotic control. Improved degradation rates can be attributed to enrichment of (1) OHRB able to also utilize Mn oxides as a terminal electron acceptor and (2) non-dechlorinating community members of the order Clostridiales and Deltaproteobacteria who provide essential co-factors to OHRB. In contrast, 100 µmol permanganate treatment disrupted biodegradation activity beyond cis-DCE and caused at least a 2-4 orders of magnitude reduction in the abundance of all measured OHRB and rdh genes, as compared to the biotic control. High permanganate treatments yielded the development of a notably divergent microbial community, with increased abundances of organisms capable of dissimilatory Mn reduction associated with Campylobacterales and Oceanospirillales and a decrease in the abundance of known supporters of OHRB . Although OTUs classified as syntrophic members of the order Clostridiales and OHRB increased in abundance over the course of 213 days of incubation following the final 100 µmol permanganate treatment, only limited regeneration of PCE biodegradation was observed in one of three microcosms, suggesting that strong chemical oxidation treatments can irreversibly disrupt OHR. Overall, this detailed investigation into microbial community structure changes due to permanganate treatment provides insight into the mechanisms of OHR stimulation or disruption upon chemical oxidation.