Reductive dechlorination of methoxychlor by bacterial species of environmental origin: evidence for primary biodegradation of methoxychlor in submerged environments.

Methoxychlor [1,1,1-trichloro-2,2-bis(4-methoxyphenyl)ethane] is an organochlorine insecticide that undergoes dechlorination in natural submerged environments. We investigated the ability to dechlorinate this compound in seven environmental bacterial species ( Aeromonas hydrophila , Enterobacter amnigenus , Klebsiella terrigena , Bacillus subtilis , Achromobacter xylosoxidans , Acinetobacter calcoaceticus , and Mycobacterium obuense ) and the enteric bacterium Escherichia coli as a positive control. In R2A broth at 25 °C under aerobic, static culture, all species except Ach. xylosoxidans were observed to convert methoxychlor to dechlorinated methoxychlor [1,1-dichloro-2,2-bis(4-methoxyphenyl)ethane]. The medium was aerobic at first, but bacterial growth resulted in the consumption of oxygen and generated microaerobic and weakly reductive conditions. Replacement of the headspace of the culture tubes with nitrogen gas was found to decrease the dechlorination rate. Our findings suggest that extensive bacterial species ubiquitously inhabiting the subsurface water environment play an important role in the primary dechlorination of methoxychlor.