ISOLATION AND MOLECULAR CHARACTERIZATION OF POTENTIAL LAMBDA CYHALOTHRIN DEGRADING BACTERIA

Abstract

Synthetic Pyrethroids are now extensively used for the improvement of crop production and quality in Pakistan. Along with the advantages, pyrethroids are also regarded as potentially harmful pollutants and pose a serious threat to organisms and environment. The present study is designed to evaluate the efficiency of different bacterial strains isolated from water and soil samples to degrade the pesticide Lambda Cyhalothrin (LC), a known synthetic pyrethroid. The residues of LC have been detected in runoff water, irrigation water, and soil and even on fruits and vegetables. The sampling area was selected as Rawal Lake and water samples were collected from four streams namely Nurpur, Ratahutar, Jinnah, Shahdara streams and Korang River that ultimately flow into the Rawal Lake. Soil samples contaminated with the pesticide were also collected from along streams and from agricultural fields around Rawal Lake. Physico-chemical characterization of water samples was also performed. Isolated LC degrading bacterial strains were taxonomically characterized on the basis of their morphology, gram staining, biochemical tests and phylogenetic similarity index of 16S rRNA gene sequence. A total of 20 different colonies were isolated from water and soil and purified by streak plate method. The strains were acclimatized by inoculating them into MSM (minimal salt medium) and Nutrient broth containing initial concentration of Lambda cyhalothrin (100 mg/L) as a sole source of carbon and energy. Optical cell density was also monitored with the help of UV-visible spectrophotometer at 600 nm. On the basis of screening, four strains were selected and identified as Bacillus circulans and Bacillus aryabhattai (isolated from soil) and Pseudomonas aeruginosa and Proteus mirabilis (isolated from water). Batch experiments were performed for degradation studies and percentage removal of Lambda cyhalothrin was determined through Chemical Oxygen Demand (COD). The strain, Pseudomonas aeruginosa has proved to be proficient bacteria by producing auspicious results in both MSM and NB media with the removal efficiency of 85 and 93.84% of Lambda cyhalothrin after 72 hours, respectively. Biodegradation kinetic model was also applied. The values of the coefficient of determination (R2) were 0.9535 and 0.946 in MSM and NB respectively, which confirmed the applicability of the model on the experimental data. The kinetic parameters μmax, Ks and Ki were also determined. Thus, Pseudomonas aeruginosa may tolerate lambda cyhalothrin more competently as compared to other strains and may play a vital role in the bioremediation of environmental contamination of pyrethroids.