| Anaerobic reductive dechlorination of chloroethene pollutants in the environment do not always go to completion, often resulting in accumulation vinyl chloride (VC). The presence of VC in drinking water source zones threatens public health since VC is known as a human carcinogen and neurotoxin. Bioremediation applications involving aerobic, VC-assimilating bacteria offer a promising potential solution for removing environmental VC cancer risk, but their evolution and activity in the environment are poorly understood. In this study, adaptation of ethene-assimilating mycobacteria to VC as a growth substrate was investigated to test the hypothesis that VC-assimilating bacteria arise from naturally occurring ethene-assimilating bacteria. In addition, VC adaptation mechanisms in two VC-adapted variants JS623-E and JS623-T were investigated.;All four Mycobacterium strains adapted to VC as a growth substrate, but the overall adaptation times, initial VC consumption patterns, and the changes in OD600 varied among the strains, growth substrate prior to VC adaptation, and the initial VC concentration. VC adaptation resulted from a genetic change and all cultures were pure.;We performed detailed investigations of VC adaptation mechanisms in JS623 variants. The activities of epoxyalkane:coenzyme M transferase (EaCoMT) in cell extracts of 623-E and 623-T (400 and 1800 nmol/min-mg protein, respectively) were higher than those in wild-type (200), and in both variant cultures, epoxyethane no longer accumulated during growth on ethene. In JS623-T, intracellular CoM concentrations in cell extracts (141%) and relative band intensity of the EtnE polypeptide on SDS-PAGE (162%) were higher than those of wild-type. In JS623-E, protein expression in response to VC and ethene differed from that of both the wild-type and JS623-T. Two missense mutations (W243G, R257L) in etnE developed in both variants after continued exposure to VC. Heterologous expression of the variant etnE alleles from strain JS623 showed etnE from both the variants had higher activity than the wild-type.;Overall, these results show ethene-assimilating mycobacteria can adapt to VC and revealed several possible VC adaptation mechanisms. The evidence suggests that etnE missense mutations played a major role in the EaCoMT activity increases observed in both variants. |
