Biodegradation of Cypermethrin by a Pseudomonas Strain Cyp19 and its use in Bioremediation of contaminated soil

摘要

Pyrethoids are commonly used insecticide in both agricultural and urban environments. In this paper we describe isolation of a bacterium capable of degrading cypermethrin. The bacterium was isolated from a pesticide contaminated soil by enrichment technique with continuous pressure of cypermethrin as the sole carbon source and energy. Morphological, physiological and biochemical characterization of the bacterium indicated that it was a Pseudomonas species. The degradation ability of the isolate determined by resting cells study revealed that strainCyp19degrades cypermethrin upto 100% within two days. Degradation of cypermethrin in unautoclaved inoculated and autoclaved inoculated soil was 97.5% and 95% respectively after 30-days of incubation studies, whereas it was insignificant in unautoclaved (uninoculated) and autoclaved (uninoculated) soil. The addition of strain Cyp19 (106 cells g-1) to soil with a low indigenous population of cypermethrin degrading bacteria treated with 40 ppm of cypermethrin g-1 resulted in a higher degradation rate than was observed in noninoculated soils. These results highlight the potential of this bacterium to be used in cleanup of contaminated pesticide waste in the environment. Introduction The contamination of ecosystem is due to pesticide discharges from manufacturing plant, agricultural runoff, leaching, accidental spills and other sources. Pyrithoids are commonly used insecticides in both agriculture and urban settings, their use may further increase as the use of organophosphate insecticides is restricted. The photostable pyrethroids represent over 25% of the world?s foliar insecticide market (Leahey, 1985) and have high toxicity to benthic aquatic organisms (Gilliom, 2001 and Hill, 1989). They exhibit high insecticidal activity combined with low mammalian toxicity (Elliott, et al., 1978) consequently, they are replacing some of the more toxic and environmentally persistent organochlorine compounds (Leahey, 1985). The importance of microbial mediated pyrethroid breakdown in soil has been demonstrated by several workers (Chapmen, et al 1981; Williams and Brown., 1978). Many approaches to pesticide treatment have been considered by the researchers (Yu, 2002; Huston and Pignatello, 1999; Arnol, et al., 1995). In view of this, bioremediation i.e. biological method has been proven to be a suitable for treatment of pesticide polluted aquifers that could be implemented either in situ or off-site in especially designed reactor or waste water treatment plants (Tartakouvsjy, et al., 2001; Kumaran and Shivaraman., 1988). However, previous studies (Kaufman et al, 1977; Lord, et al., 1982; Ohkawa et al., 1978) have failed to demonstrate the transformation of pyrethroids by axenic cultures. More recently much effort has been to develop and isolate organisms that can degrade complex compound like biphenyls, polychlorinated biphenyle, DDT, hexachloro cyclo hexane (Lal et al., 1995). Among the different genera of bacteria degrading pesticide, the genus Pseudomonas has special status to metabolize a broad range of organic compounds and therefore an ideal choice for degradative biotechnologies. The purpose of this investigation was to isolate pyrethroid – degrading microorganism. In the present study, we report the isolation and characterization of a Pseudomonas sp. capable of degrading cypermethrin at higher concentration both in pure culture as well as in the soil. Material and Methods Soil sample and ChemicalsSoil sample was taken from pesticide and nonpesticide contaminated field of Chaudhary Charan Singh Haryana Agricultural University, Hisar – (Haryana). The pesticide used was purchased from Sigma or Aldrich, USA. Analytical and spectroscopic grade hexane and acetone was purchased from E. Merck, Germany. All other chemicals were of high purity grade commercially available.Isolation of Cypermethrin degrading bacteria Approximately 10 g of soil sample was suspended in 250 ml minimal medium supplemented wi