Assessment of heavy metals content and diversity of mercury-tolerant bacteria in heavy metal-polluted environmental samples and mercury bioremediation ability of isolated strains

Abstract

• Heavy metals content in environmental samples is above the permissible limit. • Diverse mercury-tolerant bacteria is identified in heavy metal contaminated sites. • The study offers potential mercury-tolerant bacteria for bioremediation application. • Serratia quinivorans DCS_A1 reduces mercury content in multifold within 72 h. • Native isolates DCL_26, DCS_A1, and R_24 significantly lower mercury phytotoxicity. Mercury contamination disrupts ecosystems by causing toxicity and bioaccumulation in higher trophic levels. This study inspected the heavy metals content and the culturable diversity of mercury-resistant and detoxifying bacteria in samples from dumping site, thermal power plant and sewage treatment plant situated in/near Chandigarh, India. Most of the analyzed heavy metals were found above the permissible limit in these sites. Among 87 isolated bacteria, 45 could resist >200 µM ionic mercury (HgCl 2 ). Markedly, 10 and 4 isolates harbored the key genes required for mercury detoxification, merA and merB gene, respectively. The merA gene-containing strain's phylogeny indicated the resistant strains belong to Alphaproteobacteria, Betaproteobacteria , Bacilli and Gammaproteobacteria . Nine isolates could volatilize HgCl 2 efficiently, while two could volatilize organic mercury (CH 3 HgCl). The isolates Niallia circulans DCL_26, Serratia quinivorans DCS_A1, and Pseudomonas hibiscicola R_24 were found to resist and volatilize up to ≥300 μM HgCl 2 . Appreciably, S. quinivo…