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

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 soils. Three potent LC-degrading bacteria, Brucella intermedia Halo1, Alcaligenes faecalis CH1S, and Aquamicrobium terrae CH1T, were isolated from a pyrethroid-contaminated soil. A consortium CHST comprising these three 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 pesticide (i.e., LC) concentration (PC), by applying Taguchi design of experiment. The contributions of these factors to the biodegradation of LC were found to be in the order of pH > CS > PC > ID. The enhanced degradation of LC (84%) was attained at pH 7.0 in minimum salt medium containing 10 mg L^-1 LC and 3% inoculum. The consortium CHST was also augmented in sterilized and unsterilized soil microcosms at three PCs, i.e., 2, 5, and 10 mg kg^-1. After 21 d of incubation, complete LC degradation was achieved at 2 mg kg^-1 PC in sterilized as well as unsterilized soil, whereas at higher PCs, the extent of degradation was comparatively less. At PC of 5 mg kg^-1, 88% and 96% LC degradation were observed in sterilized and unsterilized soils, respectively, compared to 79% and 90% degradation at 10 mg kg^-1, respectively. During biodegradation, the major metabolite of LC, i.e., 3-phenoxybenzoic acid, was produced and further degraded. In a cotton-planted soil spiked with 10 mg kg^-1 LC, the consortium degraded 91.8% LC, as well as improving the agronomic parameters of the cotton plants. In a nutshell, the consortium CHST was found to be a promising candidate for the remediation of LC contamination at the point source.