Environmental science & technology

Enhanced biodegradation of beta- and delta-hexachlorocyclohexane in the presence of alpha- and gamma-isomers in contaminated soils.

PMID 15984776


The chlorinated insecticide hexachlorocyclohexane (HCH) has been used extensively in the past, and contaminated sites are present throughout the world. Toward their bioremediation, we isolated a bacterium Pseudomonas aeruginosa ITRC-5 that mediates the degradation of all the four major isomers of HCH under aerobic conditions, both in liquid-culture and contaminated soils. In liquid-culture, the degradation of alpha- and gamma-HCH is rapid and is accompanied with the release of 5.6 micromole chloride ions and 4.1 micromole CO2 micromole(-1) HCH-isomer. The degradation of beta- and delta-isomers is slow, accompanied with the release of 0.9 micromole chloride ions micromole(-1) HCH-isomer, and results in a transient metabolite 2,3,4,5,6-pentachlorocyclohexan-1-ol. The strain ITRC-5 also mediates the degradation of alpha-, beta-, gamma-, and delta-isomers in contaminated soils, where degradation of otherwise persistent beta- and delta-HCH is enhanced severalfold in the presence of alpha- or gamma-HCH. The degradation of soil-applied beta- and delta-HCH under aerobic conditions has not been reported earlier. The isolate ITRC-5 therefore demonstrates potential for the bioremediation of HCH-wastes and contaminated soils.