ABSTRACT
Remediation of metal-contaminated environments is particularly challenging given that, unlike organic molecules, metals cannot be biodegraded or mineralized. As such, remediation approaches must focus either on changing the redox state of a metal contaminant to a less toxic form, or on physically removing the metal from the environment. Biological processes can play a central role in the remediation of metal-contaminated water, soil, and sludge as microbes are well known to interact with, and change the properties of, a wide range of toxic and nontoxic metals. For example, metals may be used as electron donors or electron acceptors for energy production within a cell, may be used to shuttle electrons between organisms in syntrophic relationships, or possibly used as cofactors for intracellular and extracellular enzymatic reactions (Croal et al., 2004; Haferburg and Kothe, 2007). Microorganisms have, therefore, evolved mechanisms to oxidize, reduce, transport, bind, and sequester metals to either avoid toxic effects or to assist with basic cellular processes. These physiological responses to metals can be harnessed for bioremediation (Gadd, 2010; Singh et al., 2007; Van Hamme et al., 2006), and the focus of this chapter is on the use of biosurfactants for mobilizing and removing metals from contaminated environments. Specically, the mechanisms underlying biosurfactant-metal interactions will be described together with applied examples of the use of biosurfactants for treatment of metal-contaminated industrial efuents and contaminated sites.
