González, J.M., R.P. Kiene and M.A. Moran. In Press.
Transformations of sulfur compounds by an abundant lineage of marine
bacteria in the alpha-subclass of the Proteobacteria.
Applied and Environmental Microbiology.
Members of a group of marine bacteria that is numerically important in
coastal seawater and sediments were characterized with respect to their
ability to transform organic and inorganic sulfur compounds. Fifteen
strains representing the Roseobacter group (a phylogenetic cluster of
marine bacteria in the alpha-subclass of Proteobacteria) were
isolated from seawater, primarily from the southeastern U.S. Although over
half the isolates were obtained without any selection for sulfur metabolism,
all were able to degrade the sulfur containing osmolyte dimethylsulfoniopropionate
(DMSP), with production of dimethylsulfide (DMS). Five isolates also
degraded DMSP with production of methanethiol, indicating the unusual
occurrence of both cleavage and demethylation pathways for DMSP in the same
organism. Five isolates were able to reduce DMSO to DMS, and several also
degraded DMS and methanethiol. Sulfite oxygenase activity and methanesulfonic
acid oxygenase activity were also present for some of the isolates. The
ability to incorporate reduced sulfur in DMSP and methanethiol into cellular
material was studied in one of the isolates. A group specific 16S rRNA probe
indicated that uncultured bacteria in the Roseobacter group increase
in relative abundance in seawater enriched with DMSP or DMS. Because this
group typically accounts for >10% of the 16S rDNA pool in coastal seawater
and sediments of the southern U.S., clues about its potential biogeochemical
role are of particular interest. Studies of culturable representatives suggest
that the group could mediate a number of steps in the cycling of both organic
and inorganic forms of sulfur in marine environments.