Biodegradation of organochlorinated pesticides by indigenous soil microorganisms

Abstract

Biodegradation of Organochlorinated Pesticides by Indigenous Soil Microorganisms Endosulfan is a broad spectrum organochlorinated insecticide extensively used all over the world to enhance the agricultural production. Its widespread application creates severe ill effects on human and environment. The present study was aimed to isolate and identify the bacterial strains that have capability to metabolize endosulfan. Initially, eight bacterial isolates were screened out on minimal salt medium, but two more efficient bacterial isolates i.e., EN-1 and TAH were identified on the basis of 16S rRNA technique. Both isolated bacterial strains had the ability to utilize endosulfan as a sole sulfur source. These isolates were named as Stenotrophomonas maltophilia (EN-1) and Pseudomonas sp (TAH). Degradation study was conducted at various initial concentrations of endosulfan, i.e., 5, 25, 50, 75 and 100 mg/L along with the different incubation temperatures i.e., 25, 28, 32, 37 and 45ºC. The maximum endosulfan degradation by EN-1 and TAH was recorded at 32ºC and 28ºC respectively. It was observed that these bacterial isolates could degrade 80-85 % of endosulfan in 5 days of incubation, but the maximum degradation (80-85 %) was recorded when 100 mg/L of endosulfan was spiked. GC-MS analysis revealed that endosulfan diol and endouslfan lactone were major metabolites accumulated. Therefore, it was confirmed that both isolates followed hydrolytic pathway for endosulfan degradation instead of oxidative. Biodegradation kinetics of EN-1 and TAH were also studied at various initial endosulfan concentrations ranging from 5- 100 mg/L. Growth dependent and independent kinetic models were applied to access the rate of endosulfan biodegradation. The average ratio of µmax/ Ks increased when endosulfan used as a sole sulfur source, while its value decreased when additional sulfur source was added along with endosulfan. So it was found that additional sulfur did not enhance the rate of endosulfan degradation. In the present study plasmid DNA was also cured in order to locate the degrading genes. Endosulfan degrading genes were found on chromosomal DNA in EN-1 bacterial strain while TAH had plasmid borne genes. These plasmid mediated degrading genes were identified by cloning. The resulted clone product showed 97 % similarity with Nta monooxygenase gene. Comparative protein analysis was done by the SWATH MS technique. This was the first study in which the quantification and identification of bacterial proteome by using cell lysate. Out of total, 48 proteins were similar in both isolated bacterial strains which were suspected to be involved in the endosulfan degradation. Among these 48 proteins, 10 proteins were involved in various enzymatic functions. Thus, there might be 10 proteins involved in the degradation of endosulfan. All other proteins were unknown in their function.