Bioaugmentation of a novel bacterial consortium in cotton-planted soil for degradation of lambda-cyhalothrin

Abstract

Extensive use of lambda-cyhalothrin (LC) for agricultural and domestic pest control leads to the accumulation of its residues in soil and water, which poses a serious threat to the environment. Remediation of LC at the point source is the most effective way to avoid its spread and harmful effects. Therefore, this study was planned to investigate the potential of indigenously isolated bacteria for the remediation of LC in cotton-vegetated soil. Three potent LC-degrading bacteria, Brucella intermedia Halo1, Alcaligenes faecalis CH1S, and Aquamicrobium terrae CH1T, were isolated from pyrethroid-contaminated soil. A consortium CHST comprising these strains was found to exhibit a higher potential for LC degradation as compared to the individual strains. The degradation of LC by CHST was optimized for four varying factors, i.e., pH, inoculum density (ID), carbon source (CS), and initial LC concentrations (PC), by applying the Taguchi design of experiments (DOE). The contribution of each factor to the biodegradation of LC was found in the order: pH > CS > PC > ID. The enhanced degradation of LC (84%) was attained at pH 7.0 in minimum salt medium (MSM) containing 10 mg/L LC and 3% inoculum. The consortium CHST was also augmented in sterilized and un-sterilized soil microcosms at three initial LC concentrations, i.e., 2, 5, and 10 mg/Kg. After 21 days of incubation, complete LC degradation was achieved at 2 mg/Kg initial concentration in sterilized as well as un-sterilized soil, whereas at higher concentrations, the extent of degradation was comparatively less. At 5 mg/Kg, 88 and 96% LC-degradation was observed in sterilized and un-sterilized soil respectively, compared to 79 and 90% degradation at 10 mg/Kg. During biodegradation, the major metabolite of LC, i.e., 3-phenoxybenzoic acid (3-PBA), was formed and further degraded. In the cotton-planted soil spiked with 10 mg/Kg LC, the consortium degraded 91.8% LC as well as improved the agronomic parameters of the cotton plant. In a nutshell, the consortium CHST was found to be a promising candidate for the remediation of LC contaminants at the point source.