Microbe-Mediated Bioremediation: Degradation of Chlorpyrifos Pesticide and Bio-absorptive Removal of Trace Metals and Heavy Metals

Abstract

Xenobiotic compounds are synthetic or man-made compounds which are generally toxic and are not found naturally in the environment; from the Greek words Xenos (stranger) and bios (life). Pesticides and heavy metals fall into this category and can be a very serious threat to the society. The runoff of pesticides and heavy metals from agricultural fields, and as an end product of industrial waste, gets dumped in waterbodies and pollutes the water as well as the soil. Tainted water and soil become poisonous; drinking it can lead to a multitude of illnesses and deadly issues. Microbes, by catabolizing complex organic pollutants, convert them to simpler non-toxic byproducts like carbon dioxide, water and biomass with the help of enzymes and provide an environmentally sustainable mechanism for bioremediation. The present study is designed to isolate and characterize the bacterial strains isolated from the polluted water samples which are able to tolerate the high level of heavy metals such as magnesium (Mg), iron (Fe) and chromium (Cr) and the organophosphate pesticide chlorpyrifos. Isolates that can help in the bioremediation of co-contaminated environments. In this study water samples were collected from different sampling sites in the Najafgarh drain which is the largest drain and is mainly polluted by heavy metals and pesticide residue from mixed pollution in Delhi, India. The minimal salt medium (MSM) was used for the enrichment cultures and was supplemented with chlorpyrifos as a carbon source (50-100mg/L) and with different gradient concentrations of heavy metals (100 to 1000mg/l) in isolation and in combination along with magnesium and iron (100 to 1000mg/l) in isolation and in combination. Isolation of tolerant colonies was achieved by serial dilution and spread plating on nutrient agar media containing stressors with subsequent quantitative assessment of the tolerance level by determining the maximum tolerable concentration (MTC) in broth culture and plate assay. The selected isolates with good growth under stress conditions were further studied morphologically, physiologically and biochemically. FTIR, GC-MS and ICP-MS analysis helped to check the degradation potential. The 16S rRNA gene sequence was amplified, aligned with the 16S rRNA gene sequence in NCBI, and the phylogenetic analysis of the gene sequence was done by neighbour-joining method in MEGA software. The bacterial isolates are characterised and shown to be highly potential candidates for bioremediation strategies. However, more investigations are needed on degradation kinetics and metabolic pathways, as well as field-scale experiments on bioaugmentation, to confirm the practical application of these studies in environmental rehabilitation.