Characterization of multiple trichloroethene, cis-dichloroethene and 1,1-dichloroethene degrading propanotrophic...

Aerobic cometabolism offers a viable strategy for the remediation of chlorinated solvent plumes at oxic sites where anaerobic approaches are limited. Here, propane-enriched mixed cultures (derived from agricultural soils and an impacted site sediment) which previously degraded 1,4-dioxane, were evaluated for their capacity to also degrade trichloroethene (TCE), cis-1,2-dichloroethene (cDCE), and 1,1-dichloroethene (1,1-DCE) over successive transfers. Sustained biodegradation of TCE and cDCE was observed across multiple enrichments and cultures enriched on one compound generally degraded the other. In contrast, 1,1-DCE biodegradation was restricted to a subset of cultures and removal times increased over transfers. Further, 1,1-DCE removal was absent at elevated concentrations, both trends consistent with inhibitory or toxic effects. Whole genome sequencing analyses revealed pronounced substrate-dependent selection of microbial communities, with cDCE-degrading cultures being dominated by Mycobacterium and Mycolicibacterium, whereas TCE-degrading cultures were dominated by Rhodococcus. Rhodococcus metagenome-assembled genomes (MAGs) in the TCE degrading cultures classified as R. opacus or R. wratislaviensis. 1,1-DCE degrading cultures were dominated by Pseudonocardia, although the associated MAGs contained a truncated propane monooxygenase alpha subunit, suggesting other enzymes were responsible for 1,1-DCE transformation. Functional gene analysis identified both group 5 (prmABCD) and putative group 6 propane monooxygenases (although their expression was not examined). Together, these results demonstrate that substrate-specific pressures govern propanotrophic community structure and function, and highlight distinct roles of key actinobacterial genera in chlorinated ethene cometabolism. These findings support the development of propane-based bioaugmentation strategies for the treatment of mixed chlorinated solvent contamination under aerobic conditions.