Transformations of Dimethylsulfide - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 292

2.1.3.3 Extracellular Dimethylsulfoxide Reduction
in Shewanella oneidensis

The DMSO respiration system of Shewanella oneidensis is a special case as it is
located in the outer membrane rather than in the periplasmic space (Figure 7 ). The
core catalytic subunits of this complex, DmsA and DmsB, have high homology to
the E. coli DMSO reductase, but homologues of the DmsC membrane anchor
protein are absent from the S. oneidensis genome [ 165 ]. Instead, the two
S. oneidensis gene clusters (SO_1427-SO_1432, dmsEFABGH ; SO_4362-
SO_4357) encoding DmsAB-related protein complexes encode homologues of
proteins involved in metal reduction, MtrAB ('DmsEF' in the Shewanella DMSO
reductase complex), that can mediate outer membrane attachment and electron
transfer across the bacterial periplasm as well as a molecular chaperone ('DmsG')
and an 'accessory protein' ('DmsH') of 155 aa. Within the second gene cluster, the
dmsGH homologous genes are located upstream of the mtrAB related genes.

Figure 7 Structure and
cellular organization of the
Shewanella oneidensis
outer membrane DMSO
reductase in the bacterial
cell envelope. MQ/MQH 2 ,
menaquinone/menaquinol;
cyt. c , cytochrome c ; broken
arrows indicate transient
protein interactions.

Only the dmsEFABGH (SO_1427-SO_1432) operon shows significant induction
during anaerobic growth and was shown by mutagenesis studies to be the main
DMSO respiratory gene cluster in S. oneidensis [ 166 ] . Electron transfer to the
DMSO reductase complex requires menaquinone as the electron donor, and pro-
ceeds via

the CymA membrane-bound tetraheme cytochrome and the