Anaerobic dechlorination and degradation of hexachlorocyclohexane isomers by anaerobic and facultative anaerobic bacteria

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Abstract
Screening studies with strict and facultative anaerobic bacteria showed that Clostridium app. and several other representatives of Bacillaceae and Enterobacteriaceae actively degraded γ-hexachlorocyclohexane (γ-HCH) under anaerobic conditions. Representatives of Lactobacillaceae and Propronibacterium were inactive. With 36Cl-labelled γ-HCH a nearly complete dechlorination was shown to occur in 4–6 days by Clostridium butyricum, C. pasteurianum and Citrobacter freundii, while other facultative anaerobic species were less active. Aerobically grown facultative anaerobes also dechlorinated actively γ-HCH during subsequent anaerobic incubation with glucose, pyruvate or formate as substrates. The α-, β- and δ-HCH isomers were also, but more slowly, dechlorinated (γ>α>β≥δ-HCH). All species active in anaerobic degradation of γ-HCH formed γ-tetrachlorocyclohexene (TCH) as the main intermediate metabolite and no γ-pentachlorocyclohexene (PCH) or other isomers of TCH or PCH have been found. Small amounts of tri- and tetrachlorinated benzenes have been found too. The mechanism of dechlorination is discussed.