Iron oxidizing bacteria: insights on diversity, mechanism of iron oxidation and role in management of metal pollution

Abstract

In natural ecosystems, diverse iron oxidizing bacteria are of common occurrence. Basically, two different mechanisms have been proposed for catalysis of iron oxidation by bacterial metabolic systems which differ mainly at cytochrome and rusticyanin level. Biological iron oxidizers not only affect the cycling of iron but also efficiently minimize the concentrations of hazardous metals such as lead, nickel, copper, chromium, cadmium and cobalt. The ferric iron generated after biological oxidation forms complexes with metals/metalloids present in their vicinity. Ferric ions produced by biological actions also act as catalyst for oxidation of toxic metalloid such as arsenite (As III) converting it into less toxic form. Most importantly, bacterial iron oxidizers have commercially been employed in industrial bioleaching for the recovery of important elements and remediation of acid mine drainage water. Currently, heavy metal contamination has emerged as one of the prime concerns for the world and is posing serious threats to both environment and human health. Although varieties of physical and chemical techniques are currently being used to manage the metal contamination, treatment using biological iron oxidation approaches are convincing because of their ecofriendly nature and low sludge generation. In the present review we have tried to focus on the diversity of bacterial iron oxidizers, mechanisms of iron oxidation by bacterial species, and role of bacterial iron oxidizers in bioremediation of metal pollutants along with future research possibilities in this area.