Biodegradation of malathion by Brevibacillus sp. strain KB2 and Bacillus cereus strain PU

We report here the degradation of a pesticide, malathion, by Brevibacillus sp. strain KB2 and Bacillus cereus strain PU, isolated from soil samples collected from malathion contaminated field and an army firing range respectively. Both the strains were cultured in the presence of malathion under aerobic and energy-limiting conditions. Both strains grew well in the medium having malathion concentration up to 0.15%. Reverse phase HPLC-UV analysis indicated that Strain KB2 was able to degrade 72.20% of malaoxon (an analogue of malathion) and 36.22% of malathion, while strain PU degraded 87.40% of malaoxon and 49.31% of malathion, after 7 days of incubation. The metabolites mal-monocarboxylic acid and mal-dicarboxylic acid were identified by Gas chromatography/mass spectrometry. The factors affecting biodegradation efficiency were investigated and effect of malathion concentration on degradation rate was also determined. The strain was analyzed for carboxylesterase activity and maximum activity 210 ± 2.5 U ml(-1) and 270 U ± 2.7 ml(-1) was observed for strains KB2 and PU, respectively. Cloning and sequencing of putative malathion degrading carboxylesterase gene was done using primers based PCR approach.