Bioremediation of Multi-Heavy Metal Contaminated Lake Sediments Using Indigenous Bacterial Isolates and Consortium

Abstract

Heavy metal contamination of freshwater sediments poses a serious threat to aquatic ecosystems and public health due to the persistence, toxicity and bioaccumulative nature of metals. The present study investigated the isolation, identification and bioremediation potential of indigenous heavy metal tolerant bacteria from the sediments of Koradi Lake, Maharashtra, India. Sediment samples were serially diluted and cultured using standard microbiological techniques to enumerate and isolate bacterial populations. Pure cultures were characterized based on morphological, biochemical and molecular analyses. Identification was confirmed through 16S rRNA gene sequencing, followed by phylogenetic analysis using the neighbour-joining method. Four dominant bacterial isolates were identified as Bacillus subtilis, Enterobacter aerogenes, Escherichia coli and Streptococcus pneumoniae. The heavy metal tolerance and remediation efficiency of individual isolates and an optimized bacterial consortium were evaluated against selected metals, including Ba, Fe, Cu, Pb, Cd, Cr, and Zn, under controlled experimental conditions. Comparative analyses were conducted using untreated and sterile sediment controls to assess the role of microbial activity in metal reduction. Results demonstrated minimal heavy metal reduction in sterile sediments (0.5-3%), whereas non-sterile controls showed slightly higher removal (2.9-6.8%), confirming the contribution of indigenous microbial activity. Individual bacterial strains exhibited moderate remediation efficiencies, with metal reduction ranging from 12% to 38%, depending on the metal and bacterial species. In contrast, the bacterial consortium achieved the highest remediation performance, with removal efficiencies ranging from 29% to 59% after four weeks of incubation. Among the tested metals, lead (Pb), copper (Cu), and cadmium (Cd) showed the greatest reduction in the consortium-treated sediments. This study demonstrates that indigenous bacterial consortia represent a cost effective, eco-friendly, and sustainable strategy for the bioremediation of heavy metal polluted freshwater sediments and offers valuable insights for the development of in situ remediation approaches in contaminated aquatic environments.