Concurrent degradation of dimethyl phthalate (DMP) during production of Bacillus thuringiensis based biopesticides

Bacillus thuringiensis var. kurstaki (Btk) predominantly used as a microbial insecticide was tested for concomitant degradation of dimethyl phthalate (DMP). Different concentrations of DMP, 100, 200, 500, 1000 and 2000 mg/l were initially spiked in tryptic soya broth medium. A control of tryptic soya broth without DMP was also included. The experiments were carried out for 48 h at 30 degrees C and 250 rpm and growth, enzyme and biocontrol assay was evaluated. DMP concentration until 500 mg/l did not affect Btk cell growth, however, for DMP concentration of 1000-2000 mg/l, there was a 10 and 100 times decrease in cell and spore concentration, respectively. The enzyme concentration reduced by a factor of 1.5, 2, and 2.3 times for protease, esterase and amylase, respectively, at 1000 and 2000 mg/l suggesting toxicity of DMP at higher concentrations. Interestingly, the entomotoxicity (insect toxicity, taken as measure of biocontrol) was higher at 1000 and 5000 mg/l with 12 and 13 billion spruce budworm units/l, as tested against spruce budworm larvae. After 48h of incubation, DMP concentration decreased to 1-3mg/l at initial concentrations ranging from 100 to 500 mg/l, and the removal was relatively lower with 89 and 87% at 1000 and 2000 mg/l of DMP, respectively. These results suggest that Btk produces panoply of enzyme systems which can assist in degradation of DMP.