Biodegradation of Endosulfan by Pseudomonas fluorescens

Abstract

The endosulfan-degrading bacterial strain Pseudomonas fluorescens was isolated, and degradation of endosulfan by freely suspended and calcium-alginate entrapped bacterial cells were investigated in batch as well as in packed bed column studies. Freely suspended Pseudomonas fluorescens cells with biomass maximum OD/OD0 value of 1.68 at 610 nm could degrade endosulfan with an initial concentration of 350.24 ± 0.83 μg/L efficiently within 12 days, thus utilising endosulfan as the sole carbon and energy source. Degradation of endosulfan occurred concomitantly with bacterial growth. The bacteria immobilised in Ca-alginate beads in batch shake flask system were tested for their ability to degrade endosulfan at different concentrations (350.24 ± 0.83, 450.39 ± 1.95 and 550.85 ± 1.84 μg/L). A total of 125 mL of Broth minimal medium of pH 7 was inoculated with 5 g of wet Ca-alginate beads (derived from a 3-mL cell suspension of 0.72 OD at 610 nm) for the study. Almost similar trends of degradation efficiencies were shown by the immobilised cells toward different concentrations of endosulfan. The complete removal of alpha and beta-isomers of endosulfan at different initial endosulfan concentrations was observed between 9 and 11 days of the experiment. Additionally, the degradation rate in batch reactors with Ca-alginate-immobilised cells also derived from a 3-mL cell suspension of 0.72 OD at 610 nm was tested and found to be marginally higher than that of free cells. Ca-alginate immobilised cells in packed bed reactors operated in a semi-continuous mode could degrade toxic alpha and beta-isomers of endosulfan (350.38 ± 1.18 μg/L) within 6 days. Thus, the method proved effective for biodegradation of endosulfan. The metabolites formed indicated that the degradation of the pesticide follows a hydrolytic pathway.