Lead- and mercury-resistant marine bacteria and their application in lead and mercury bioremediation

Abstract

With rapid industrialisation, enormous amounts of industrial waste including heavy metals have accumulated in marine environments over several decades and require special attention. Untreated wastes from mining, metal refining industries, battery manufacturing industries, sewage sludge, power plants and waste incineration plants often contain substantially high levels of lead (Pb) and mercury (Hg); when dumped into marine and estuarine waters, these pose serious threat to environmental biota and urgently need to be removed from polluted marine/estuarine sites. Lead and mercury are non-bioessential, persistent and hazardous heavy metal pollutants of environmental concern. Bioremediation of heavy metals using Pb- and Hg-resistant bacteria has become a potential alternative to the existing technologies for the removal and/or recovery of toxic Pb and Hg from waste waters before releasing it into marine/estuarine water bodies for environmental safety. Various strategies through which marine/estuarine bacteria resist high concentrations of lead/mercury include efflux mechanisms, extracellular sequestration, biosorption, precipitation, reduction, volatilisation, alteration in cell morphology, enhanced siderophore production, altered permeability, demethylation and intracellular bioaccumulation. These unique characteristics of marine/estuarine bacteria proved to be an ideal tool in bioremediation of lead and mercury from contaminated marine and estuarine environmental sites.