Effect of application of different pesticides to soybean on the soil microflora.

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.

Biomineralization of an organophosphorus pesticide, Monocrotophos, by soil bacteria.

AIMS: To study biomineralization of Monocrotophos (MCP) and identify the metabolites formed during biodegradation. METHODS AND RESULTS: Two cultures, namely Arthrobacter atrocyaneus MCM B-425 and Bacillus megaterium MCM B-423, were isolated by enrichment and adaptation culture technique from soil exposed to MCP. The isolates were able to degrade MCP to the extent of 93% and 83%, respectively, from synthetic medium containing MCP at the concentration of 1000 mg x l(-1), within 8 d, under shake culture condition at 30 degrees C. The cultures degraded MCP to carbon dioxide, ammonia and phosphates through formation of one unknown compound--Metabolite I, valeric or acetic acid and methylamine, as intermediate metabolites. The enzymes phosphatase and esterase, reported to be involved in biodegradation of organophosphorus compounds, were detected in both the organisms. CONCLUSIONS: Arthrobacter atrocyaneus MCM B-425 and B. megaterium MCM B-423 isolated from soil exposed to MCP were able to mineralize MCP to carbon dioxide, ammonia and phosphates. SIGNIFICANCE AND IMPACT OF THE STUDY: Pathway for biodegradation of MCP in plants and animals has been reported. A microbial metabolic pathway of degradation involving phosphatase and esterase enzymes has been proposed. The microbial cultures could be used for bioremediation of wastewater or soil contaminated with Monocrotophos.