A novel dimethylsulfoxide reductase family of molybdenum enzyme, Idr, is involved in iodate respiration by Pseudomonas sp. SCT.

Pseudomonas sp. strain SCT is capable of using iodate (IO ) as a terminal electron acceptor for anaerobic respiration. A possible key enzyme, periplasmic iodate reductase (Idr), was visualized by active staining on non-denaturing gel electrophoresis. Liquid chromatography-tandem mass spectrometry analysis revealed that at least four proteins, designated as IdrA, IdrB, IdrP , and IdrP , were involved in Idr. IdrA and IdrB were homologues of catalytic and electron transfer subunits of respiratory arsenite oxidase (Aio); however, IdrA defined a novel clade within the dimethylsulfoxide (DMSO) reductase family. IdrP and IdrP were closely related to each other and distantly related to cytochrome c peroxidase. The idr genes (idrABP P ) formed an operon-like structure, and their transcription was upregulated under iodate-respiring conditions. Comparative proteomic analysis also revealed that Idr proteins and high affinity terminal oxidases (Cbb and Cyd), various H O scavengers, and chlorite (ClO ) dismutase-like proteins were expressed specifically or abundantly under iodate-respiring conditions. These results suggest that Idr is a respiratory iodate reductase, and that both O and H O are formed as by-products of iodate respiration. We propose an electron transport chain model of strain SCT, in which iodate, H O , and O are used as terminal electron acceptors.