Transformations of Dimethylsulfide - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 279

environments, sulfate-reducing bacteria and methanogenic Archaea are probably
the main DMS-degrading populations [ 26 , 31 , 48 , 53 ]. However, strains able to
degrade DMS under anoxic conditions using nitrate as electron acceptor were also
identified [ 52 , 54 , 55 ].
Enzymes of DMS metabolism have been identified in methanogens. In
Methanosarcina barkeri DMS and methylmercaptopropionate (MMPA) were
converted to methane with a corrinoid protein functioning as a coenzyme M
methylase capable of DMS and MMPA degradation [ 56 ]. In Methanosarcina
acetivorans three fused corrinoid/methyl transfer proteins have been implicated
in methyl sulfide metabolism [ 57 ].
1.2.4 Dimethylsulfide Oxidation to Dimethylsulfoxide
Oxidation of DMS to DMSO has been reported for anoxygenic phototrophic purple
sulfur bacteria [ 58 ] and phototrophic green sulfur bacteria [ 59 ] where this process
provides electrons for carbon fixation [ 58 ]. DMS dehydrogenase was identified as
the enzyme for DMS to DMSO oxidation in Rhodovulum sulfidophilum [ 60 ]. The
enzyme and its encoding genes are discussed in further detail below.
Some heterotrophic bacteria were also shown to oxidize DMS to DMSO,
including isolates of Delftia acidovorans [ 61 ] and Sagittula stellata [ 62 ].
While the underlying mechanism of DMS oxidation in these isolates remains to
be identified, it was shown that DMS oxidation to DMSO provided an auxiliary
source of energy for S. stellata when growing on fructose or succinate in the
presence of DMS [ 19 ] allowing a higher growth yield to be attained. Similarly, it
was suggested that a Flavobacterium strain was able to oxidize DMS to DMSO and
might be capable of using this as an energy source [ 20 ]. The genetic and biochem-
ical basis of DMS oxidation to DMSO in these strains has not been reported.
DMSO is also a product of co-oxidation of DMS by methanotrophic and ammonia-
oxidizing bacteria [ 63 , 64 ]. In the latter, the activity was shown to be due to ammonia
monooxygenase (AMO), while it is assumed that methane monooxygenases may be
responsible in methanotrophs, owing to the close evolutionary relationship between
particulate methane monooxygenase and AMO [ 65 ] and the ability of the enzymes to
co-oxidize a range of compounds [ 66 ].
Utilization of DMS, however, is not limited to energy-generating processes.
Its use as a sulfur source has been reported for a wide range of bacteria including
strains of Marinobacter [ 22 ], Acinetobacter [ 67 ], Rhodococcus [ 21 ], and Pseudo-
monas putida [ 68 ]. In Marinobacter , a flavin-containing enzyme appeared to be
involved in the process which also required light [ 22 ]. In the other strains men-
tioned above, utilization of DMS as a sulfur source has been suggested to proceed
via oxidation to DMSO by a multicomponent monooxygenase similar to phenol
hydroxylase, followed by further oxidation to dimethylsulfone (DMSO 2 ) and
methanesulfonic acid (MSA) [ 21 , 67 , 68 ].