Microbial Bioremediation of Chromium: A promising approach of environmental microbiology

Abstract

Heavy-metal pollution represents an important environmental problem due to the toxic effects of metals, and their accumulation throughout the food chain leading to serious ecological and health problems. Metal remediation through common physico-chemical techniques is expensive and unsuitable in case of voluminous effluents containing complexing organic matter and low metal contamination. Biotechnological approaches that are designed to address to such problems have, therefore, received great deal of attention in the recent years. Microorganisms are intimately involved in metal biogeochemistry with a variety of processes determining mobility, and therefore, bioavailability and bioremediation. The balance between mobilization and immobilization varies depending on the organisms involved, their environment and physicochemical conditions. Metal mobilization can arise from a variety of leaching mechanisms, complexation by metabolites and siderophores, and methylation, where this results in volatilization. Immobilization can result from sorption to biomass or exopolymers, transport and intracellular sequestration or precipitation as organic and inorganic compounds, e.g., oxalates (fungi) and sulfides. This chapter discusses the principle of microbial-metal interaction and mechanisms of the bioremediation process and also includes the chromium bioremediation using native isolates. Some details on bio-reduction of chromium (VI) and chromium (III) from their specific sources are described to exemplify the role of metal tolerant native microbial isolates.