Vol.:(0123456789) 1 3 Environmental Sustainability https://doi.org/10.1007/s42398-018-0024-0 REVIEW Iron oxidizing bacteria: insights on diversity, mechanism of iron oxidation and role in management of metal pollution Vipin Kumar Singh 1  · Asha Lata Singh 1  · Rishikesh Singh 2  · Ajay Kumar 1 Received: 30 April 2018 / Revised: 13 August 2018 / Accepted: 17 August 2018 © Society for Environmental Sustainability 2018 Abstract In natural ecosystems, diverse iron oxidizing bacteria are of common occurrence. Basically, two diferent mechanisms have been proposed for catalysis of iron oxidation by bacterial metabolic systems which difer mainly at cytochrome and rusti- cyanin level. Biological iron oxidizers not only afect the cycling of iron but also efciently 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 con- cerns 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. Keywords Iron oxidizers · Arsenic · Bioremediation · Metal contamination · Ferric iron · Sludge Introduction Iron is one of the abundantly occurring elements on the Earth (Wedepohl 1995) and crucial for multiple biologi- cal activities. A number of oxidation states have been pro- posed for iron, but +2 (ferrous) and +3 (ferric) forms are the most common. The changes in oxidation number are afected by environmental conditions like pH, oxygen con- tent, and oxidation reduction potential. Since conversion of ferrous iron to ferric iron is highly oxygen dependent, we can expect the presence of ferrous iron, and therefore iron oxidizing bacteria, only under anoxic environments such as deep ground water surfaces or under highly acidic condition where oxidation is negligible to very slow (Bird et al. 2011). Under these oxygen depleted conditions, iron oxidizing bacteria utilize ferrous iron for oxidation to accomplish the energy requirement for carbon assimilation (Schwertmann and Cornell 2000). Among various types of iron oxidizers, bacterial iron oxidizers are widely described. Most of the bacterial iron oxidizers belong to phylum Proteobacteria. The bacterial genera performing the oxidation may be auto- trophic, heterotrophic, phototrophic, chemotrophic, aerobic and anaerobic (Bird et al. 2011). Their huge diversity in physiology and phylogeny has made them a good tool for innovative research in the area of pollution management. Iron oxidizers are the important players not only in global iron biogeochemical cycling (Bach and Edwards 2003) but also in cycling of other toxic metals and industrial biomin- ing activities (Rawlings and Johnson 2007). Therefore, there is growing attention amongst researchers on iron oxidation process, genetic regulation of iron oxidation (Bird et al. 2011), industrial application (Zhang et al. 2018), their phylo- genetic relationship, and diversity along with their adaptive * Vipin Kumar Singh vipinks85@gmail.com 1 Department of Botany, Centre of Advanced Study (CAS), Institute of Science, Banaras Hindu University, Varanasi 221005, India 2 Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi 221005, India