Biodegradation of dimethyl phthalate by an entomopathogenic nematode symbiont Xenorhabdus indica strain KB-3

Abstract

Dimethyl phthalate (DMP) a common environmental pollutant is well known for its endocrine disrupting activities. Wide spread use of the plastics and pesticides in agriculture have resulted in DMP pollution in soils. An endosymbiotic bacteria Xenorhabdus indica isolated from entomopathogenic nematode Steinernema thermophilum was investigated for biodegradation of DMP. Biodegradation experiment was conducted for 12 days in minimal salt medium supplemented with beef extract. Quantification of residual DMP by High performance liquid chromatography (HPLC) revealed that maximum degradation (98.75%) occurred at 9th day of incubation along with higher esterase activity (46.94 IU/ml) and growth of bacteria (263.75 μg/ml). The efficacy of purified esterase for degradation of DMP was also investigated. It was observed that enzyme alone transform more than 25.6% of DMP into mono-methyl phthalate (MMP) and phthalic acid (PA) within 24 h, which confirms its role in degradation of DMP. Activity of carboxyl esterase enzyme was also positively correlated (r = 0.88) with biodegradation of DMP. Xenorhabdus completely mineralized the DMP as the two intermediates mono-methyl phthalate (MMP) and phthalic acid were not detected after the incubation period of 12 days. The results suggest that the X. indica was highly efficient in degrading DMP and can be employed for bioremediation of contaminated sites.