Bioremediation of Heavy Metal Lead (Pb) by Enteric Bacteria and Metagenomic Analysis of an Endogenic Earthworm Metaphire nanaoensis Found in the Semi-urban Paddy Fields of Kamrup District, Assam

The Biodiversity of Assam, India is a major notable hot spot because of its vivid flora and fauna. Earthworms being the keystone species harbors beneficial microbes in the gut which plays a symbiotic role in degradation of pollutants. Present study reveals a high concentration of heavy metal Lead (Pb) in different paddy fields of Assam that becomes a serious threat to the ecosystem. Therefore, the above research has been conducted to evaluate the sequestration potential of lead (Pb) tolerant bacteria from an endogenic earthworm gut of Metaphire nanaoensis (OQ073567). Bacterial strains were isolated from the gut of the earthworm Metaphire nanaoensis. After screening, four isolates showing highest tolerance limit at 800 ppm were subjected to AAS and maximum sequestration of Pb was observed in Pseudomonas aeruginosa strain PSD (0.38–0.4) mg/ml followed by Bacillus sp. strain LSRBMoFPIKRGCFTRI6 (0.32–0.35) mg/ml, Bacillus subtilis strain DCK5 (0.19–0.21) mg/ml and Bacillus sp. strain HL2 (0.19–0.20) mg/ml. This highlights the significance role of the gut bacterial community in sequestration of heavy metal. Metagenomic annotation of the unculturable gut bacterial community reveals the high abundance of the genus Prevotella of unclassified bacteria (16.91%) followed by Firmicutes (10.13%), Actinobacteria (6.8%) which would further aid in exploring different pathways for degradation of xenobiotic compounds. It underlines the importance of earthworm species' native gut bacteria for enhanced biodegradation and helps in understanding of the microbial alterations in bioremediation which would be a promising method of targeting environmental pollutants.