B. Bhadbhade

Almost 30% of the precious agricultural output of India is lost owing to pest infestation. In India, pesticide consumption for protecting crops is about 3% of the total world consumption. Monocrotophos (MCP), an organophosphorus insecticide, is widely used to control insects on crops. Being readily water soluble and highly toxic, its removal from wastewater generated during manufacture becomes inevitable. Bioremediation of wastewater containing MCP by Arthrobacter atrocyaneus, Bacillus megaterium, and Pseudomonas mendocina was highest at pH 8.0, but maximum reduction in Chemical Oxygen Demand (COD) was at pH 7.0. Removal of MCP and reduction in COD by B. megaterium and Ps. mendocina were highest at 35 degrees C, while with A. atrocyaneus, it was maximum at 30 degrees C, under aerated culture condition and inoculum density of 10(8) cells/ml. Use of pure cultures for bioremediation of effluent containing MCP appears to be the first such attempt.

The insecticide resistance-associated esterase, carboxylesterase B1 (CaE B1), from mosquito was used to degrade the organophosphorus compounds. To eradicate the need for enzyme purification and minimize the resistance to mass transport of the substrate and product across the cell membranes, the CaE B1 was displayed on the cell surface of Escherichia coli fused to the C-terminus of the ice nucleation protein (INP). The presence of CaE B1 on the bacterial cell surface was verified by SDS-PAGE, Western blotting analysis, and immunofluorescence microscopy. More than 50% of active CaE B1 is exported across the membrane and anchored onto the cell surface as determined by proteinase accessibility and cell fractionation experiments. In contrast, only a 6% drop in activity for proteinase K-treated cells was detected from E.coli cells containing pET-B1. From the degradation experiment, more than 80% of the malathion was degraded by whole cells containing plasmid pUC-NC-B1. Constitutive expression of CaE B1 on the surface using INPNC resulted in no cell lysis, and the suspended cultures also exhibited good stability. Because of their high biodegradation activity and superior stability, these "live biocatalysts" are promising for detoxification of organophosphorus pesticides.

Pesticide residues contributing to the contamination of soil may influence microbial population of the soil and in turn fertility of soil. The present paper reports the effect of pesticides applied to soybean i.e. phorate, carbofuran, carbosulfan, thiomethoxam, imidacloprid, chlorpyriphos and monocrotophos on soil microflora. The viable count of rhizobia and phosphate solubilizing bacteria from rhizospheric soil of soybean ranged between 10(7)-10(8) cfu/g soil which was comparable to the count of bacteria from untreated (control) soil. No significant change in the total viable count of any kind of bacteria due to application of pesticides has been found showing their ability to degrade these pesticides.