The Tetraheme Cytochrome CymA Is Required for Anaerobic Respiration with Dimethyl Sulfoxide and Nitrite inShewanella oneidensis

Abstract

The tetraheme c-type cytochrome, CymA, from Shewanella oneidensis MR-1 has previously been shown to be required for respiration with Fe(III), nitrate, and fumarate [Myers, C. R., and Myers, J. M. (1997) J. Bacteriol. 179, 1143-1152]. It is located in the cytoplasmic membrane where the bulk of the protein is exposed to the periplasm, enabling it to transfer electrons to a series of redox partners. We have expressed and purified a soluble derivative of CymA (CymA(sol)) that lacks the N-terminal membrane anchor. We show here, by direct measurements of electron transfer between the purified proteins, that CymA(sol) efficiently reduces S. oneidensis fumarate reductase. This indicates that no further proteins are required for electron transfer between the quinone pool and fumarate if we assume direct reduction of CymA by quinols. By expressing CymA(sol) in a mutant lacking CymA, we have shown that this soluble form of the protein can complement the defect in fumarate respiration. We also demonstrate that CymA is essential for growth with DMSO (dimethyl sulfoxide) and for reduction of nitrite, implicating CymA in at least five different electron transfer pathways in Shewanella.

Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors

“…These proteins include CymA, a tetraheme c-type cytochrome anchored to the inner membrane that serves as a MQH 2 dehydrogenase [8,12,20,43,44]; Stc, a 12-kDa tetraheme periplasmic c-type cytochrome [15,45] and the periplasmic decaheme cytochrome MtrA [10] (Fig. 1).…”

Extracellular respiration of dimethyl sulfoxide by Shewanella oneidensis strain MR-1

“…5. We propose that the path of electron flow from the menaquinone pool (MQ) to the membrane-bound c-type cytochrome CymA (24) continues through the putative periplasmic decaheme cytochrome DmsE. The integral outer membrane protein DmsF could facilitate electron transfer across the outer membrane by providing a channel to mediate direct interaction between the extracellular DMSO reductase and DmsE, similar to a model for metal reduction put forward by Beliaev et al ʈ Analysis of type II secretion mutants and localization studies of DmsB in S. oneidensis provide evidence that DMSO utilization is an extracellular respiratory process.…”

“…Both homologs of DmsA in S. oneidensis (SO1429 and SO4358) contain twin arginine leader sequences at their N termini, suggesting export into the periplasm through the twin arginine translocation protein secretion pathway (23). No homolog of dmsC from E. coli is present either in the gene clusters encoding putative DMSO reductases or in the genome itself (24). Unlike the E. coli DmsA protein, SO1429 and SO4358 are predicted to be lipoproteins (www.tigr.org).…”

The periplasmic nitrate reductase in Shewanella: the resolution, distribution and functional implications of two NAP isoforms, NapEDABC and NapDAGHB

“…In addition to the catalytic NrfA subunit, NRF consists of a pentahaem cytochrome c (NrfB), an ironsulfur cluster protein on the periplasmic face of the membrane (NrfC) and a transmembrane domain (NrfD), which as the NrfABCD cluster is commonly found in cproteobacteria Hussain et al, 1994;Simon et al, 2000). The NapC homologue, CymA, has been found to be essential in S. oneidensis MR-1 for the anaerobic reduction of nitrate, nitrite, Fe(III), Mn(IV), DMSO or V(V) (Carpentier et al, 2005;Gao et al, 2009;Myers & Myers, 1997, 2000Schwalb et al, 2003). Putative CymA proteins with 68.1 % identity are encoded in the genomes of all Shewanella species that encode NAP-b.…”

“…The nap operons of the e-proteobacteria Wolinella succinogenes (napAGHBFLD) (Kern & Simon, 2008;Simon et al, 2003) and Campylobacter jejuni (napAGHBLD) do not include the napC gene. The function of NapC in NAP in these species and in S. oneidensis MR-1, which also lacks NapC, may be met by the periplasmic c-type cytochrome homologue CymA, which is also from the NapC/NirT family (Gao et al, 2009;Murphy & Saltikov, 2007;Myers & Myers, 1997, 2000Schwalb et al, 2003). The napCMADGH operon of the d-proteobacterium Desulfovibrio desulfuricans lacks the napB gene (Marietou et al, 2005).…”