Biodegradation of methidathion by Serratia sp. in pure cultures using an orthogonal experiment design, and its application in detoxification of the insecticide on crops

An enrichment culture method was applied to the isolation of a bacterial strain responsible for biodegradation of methidathion residues, from a methidathion-treated orchard. The strain (SPL-2) was identified as Serratia sp. according to its physiological characteristics and 16S rRNA gene phylogenetic analysis. Serratia sp. was able to grow in a poor medium consisting of mineral salts and using methidathion as the sole carbon source at a concentrations of 50–150 mg/L. The effects of multifactors on degradation of methidathion in pure cultures by Serratia sp. were investigated using an orthogonal experimental design L9 (34). On the basis of range analysis and ANOVA results, the most significant factors were temperature and inoculum size. The optimal conditions for methidathion biodegradation in pure cultures were a temperature in 30 °C, an inoculum size of 10 %, pH = 7 and an aeration rate of 200 rpm. Two different concentrations of strain SPL-2 fermenting liquids (OD600 = 0.2 and OD600 = 0.4) were prepared and applied to remove methidathion residues from agricultural products, and this process can be described by a first order rate model. In contrast to controls, the DT50 of methidathion was shortened by 35.7 %, 8.2 % and by 62.3 %, 57.5 % on OD600 = 0.2 and OD600 = 0.4 treated haricot beans and peaches, respectively. These results suggest that the isolated bacterial strain may have potential for use in bioremediation of methidathion-contaminated crops.