Recent advances in studies on dissimilatory Fe(Ⅲ)-reducing microorganisms

Iron is the fourth most abundant element in the Earth's crust.Microbially mediated dissimilatory Fe(Ⅲ) reduction is the major process for Fe(Ⅲ) reduction in anoxic environment.This review introduces the classification and the diversity of dissimilatory Fe(Ⅲ)-reducing microorganisms.There are two major groups of Fe(Ⅲ)-reducing microorganisms:one is microorganisms which could conserve energy to support growth from Fe(Ⅲ) reduction,and the other is those which could not conserve energy to support growth from Fe(Ⅲ) reduction.Dissimilatory Fe(Ⅲ)-reducing microorganisms are interspersed throughout Bacteria,Archaea and Fungi and have physiological diversity.Geobacter and Shewanella are the two most well studied genera among all the Fe(Ⅲ)-reducing microorganisms.This also summarizes the strategies that dissimilatory Fe(Ⅲ)-reducing bacteria use to transfer electron to extracellular Fe(Ⅲ) oxide minerals as well as the energy-generating central metabolism models of dissimilatory Fe(Ⅲ)-reducing bacteria.Direct contact,cellular appendage production,electron shuttling and chelation are the four potential strategies for the respiration of dissimilatory Fe(Ⅲ)-reducing bacteria.In Geobacter,acetate and other electron donors are completely oxidized via the tricarboxylic acid(TCA) cycle,generating ATP primarily from oxidative phosphorylation,while substrate-level phosphorylation is the primary source of energy conservation during anaerobic respiration of Shewanella.In addition,the environmental significances of dissimilatory Fe(Ⅲ)-reducing microorganisms are reviewed.Fe(Ⅲ)-reducing microorganisms might be one of the first,if not the first,of microbes involved in microbial respiration in the archaean biosphere,which contributes to the decomposition of organic matter in modern sedimentary environments and inhibition of methane production,exerts a broad range of impacts on the behavior of trace elements and have great potential in the bioremediation and microbial fuel cells.Finally,perspectives in the molecular ecology of dissimilatory Fe(Ⅲ)-reducing bacteria studies are proposed,e.g.the community structure of dissimilatory Fe(Ⅲ)-reducing bacteria in paddy soils,the contribution of dissimilatory Fe(Ⅲ)-reducing bacteria in the C-Fe-N coupling and the mechanism of dissimilatory Fe(Ⅲ)-reducing bacteria in the bioremediation with electrode and solar energy.