Biodegradation study of -hexachlorocyclohexane using selected bacteria isolated from agricultural soil

Bacterial isolates RP-1, RP-3 and RP-9 were isolated from agricultural soil using enrichment culture technique and screened positive for lindane degradation. RP-1, RP-3 and RP-9 were found to utilize and degrade higher concentrations (100 ppm) of lindane. RP-1 and RP-3 showed 69.5 and 65% lindane degradation after 10 days of inoculation where as RP-9 degraded 62% of lindane after 15 days. The estimated Cl- ion release was 49, 42 and 39 mg/mL, respectively for the three bacterial isolates. Gas chromatography was used for analysis of metabolite formed during lindane degradation and different parameters of degradation kinetics were calculated using first order kinetic equation. A drastic decrease in degradation rate was observed at initial lindane concentrations higher than 200 mg/l in the mineral media. The calculated half-life periods for RP-1, RP-3 and RP-9 were found to be 3.85, 2.77 and 4.00 days, respectively. All three isolates showed maximum degradation activity at: incubation period; 10-15 days, incubation temperatures; 30°C, pH; 7.0, shaking speed 120 rpm, initial substrate concentration; 100 mg/l. Galactose and succinate enhanced the degradation rate up to 10% whereas maltose, lactose and xylose decreased the degradation level up to 40%. Addition of glucose as a co-substrate was found highly favorable for enhancement of lindane degradation. Key words: Enrichment culture, colorimetric assay, lindane, degradation, gas chromatography.