The role of bacteria in metal bioaccumulation and biosorption

Heavy metal contamination has been of great concern due to its persistence and nonbiodegradable nature. The ineffectiveness of various conventional remediation techniques regarding technical and economic constraints leads to the search for ecofriendly and cost-effective biological methods for metal removal from the contaminated environment. Microorganisms, particularly bacteria, are well known to interact with metals through various mechanisms, such as sorption to exopolymers, precipitation, binding the metals to their cell walls (so-called biosorption), and intracellular accumulation (so-called bioaccumulation). In the last two decades, there has been a huge member of studies on bacterial bioremediation/biosorption applications; however, the actual mechanisms underlying the bioremoval process and how to improve efficiency on large-scale implementation are not clear. In this review, an attempt has been made to comprehensively understand the metal-bacteria sorption reactions (biosorption and bioaccumulation) in rendering metal resistance and to compare their metal removal efficiency.