Isolation and Acclimation of a Microbial Consortium for Improved Aerobic Degradation of α-Hexachlorocyclohexane

A microbial consortium that can utilize α-hexachlorocyclohexane (α-HCH) as a sole source of carbon and energy was isolated from soil and sewage through a novel technique involving an initial enrichment in a glass column reactor followed by a shake flask enrichment. This consortium took 14 days to completely mineralize 5 and 10 μg mL-1 α-HCH in mineral salts medium in shake flasks. The degradative ability of this consortium improved very markedly on acclimation by successive and repeated passages through media containing increasing concentrations of α-HCH. The acclimated consortium could degrade 100 μg mL-1 of α-HCH within 72 h at a degradation rate of 58 μg mL-1 day-1 with concomitant release of stoichiometric amounts of chloride. Accumulation of any intermediary metabolites was not detected in the culture broth as tested by TLC and GC, implying complete mineralization of the substrate. The acclimated consortium contained eight bacterial strains and a fungus. The individual strains and the different permutations and combinations of them, however, were able to utilize only 10 μg mL-1 of α-HCH. Mesophilic temperatures (20−30 °C) and near-neutral pH (6.0−8.0) were most favorable for α-HCH degradation. Among the auxiliary carbon sources tested, ethanol, benzoate, and glucose (at higher concentrations) retarded the degradation of α-HCH, whereas the addition of cellulose, sawdust, and low concentrations of glucose (