Isolation and Determination of Efficacy of Acephate Degrading Bacteria from Agricultural Soil

Abstract

Organophosphorus pesticides are heavily employed worldwide for their broad insecticidal spectrum and remains a major environmental pollutant. The degradation efficiency of bacteria isolated from pesticide contaminated agricultural paddy field soil was investigated against organophosphorus pesticide acephate. Five isolates identified as Lysinibacillus fusiformis ADI-01, Pseudomonas pseudoalcaligenes ADI-03, Pseudomonas species ADI-04, Pseudomonas pseudoalcaligenes ADI-06 and atypical VP negative Bacillus cereus ADI-10 were capable to degrade organophosphorus pesticide acephate up to 500 ppm concentration in mineral salt medium. The growth was evaluated by absorbance value, plating on mineral salt agar containing acephate. The degradation of pesticide was further monitored by HPLC analysis. The results reveal the potential of these bacteria on degradation of pesticide and lead to the development of bioremediation strategy to minimize pesticide contamination on land. Keywords: Acephate, Organophosphorus pesticide, Biodegradation, Bacillus cereus, Lysinibacillus fusiformis, Pseudomonas pseudoalcaligenes. I. Introduction All over the world, the use of pesticides is increasing because of the need to feed the world's ever expanding population while the amount of the land for the food production is diminishing. The increase in the use of the pesticides has increased both the hazards to human health as well as pollution of the environment (1). Worldwide, deaths and chronic illness due to pesticide poisoning amount to about 1 million (2). Among the various groups of pesticides that are being used the world over, organophosphorus group forms a major and most widely used group and accounts for more than 36% of the total world market (3). The organophosphorus pesticides are used in agriculture, gardens and veterinary practices (4). Despite their biodegradable nature, some are highly toxic and their residues are found in the environment (5). Acephate (O,S-dimethyl acetylphosphoramidothioate) is an important systemic organophosphorus insecticide with toxicity attributed to mammalian metabolism and bioactivation to methamidophos which act as an acetyl cholinesterase (AchE) inhibitor (6). Acephate was found to have longer half life than methamidophos in soil (7). Acephate does not undergo photolysis and it's half life in pH 5 to 7 is 20 days at 40 o C and it is least