Dissimilatory iron-reducing microorganisms: The phylogeny, physiology, applications and outlook

Dissimilatory iron reduction (DIR) is an important form of microbial respirations and a key part of iron biogeochemical cycle. A wide range of both bacteria and archaea that can conserve energy through Fe(III) reduction are called dissimilatory iron-reducing microorganisms (DIRMs). They have been increasingly recognized as important for coupling organic carbon oxidation in diverse anaerobic environments, such as soil, sediments, freshwater, marine water as well as extreme environments. In parallel with their phylogenetic diversity, DIRMs possess metabolic versatility, including multiple extracellular electron transfer (EET) pathways and various electron donors as well as acceptors. In this review, phylogenetic, environmental distribution of DIRMs was demonstrated comprehensively by summarizing 51 isolated DIRMs belonging to 27 genera in previous literature. EET mechanisms were further elaborated on based on four DIRMs representatives: Geobacter, Shewanella, Gram-positive bacteria and archaea. Various electron donors, acceptors, and novel metabolisms revealed recently prompt the development of DIRMs biotechnological applications, including bioleaching, bioremediation, biosynthesis, anaerobic fermentation, and production of bioelectricity. Although past decades have witnessed a great increase of the publications in DIRMs, further investigation are required for deep understanding and practical applications, such as their roles in natural environments, EET mechanisms in different DIRMs, cooperation with other microbes, and mechanisms of improved bioproduction by adding iron-oxides.