Abstract
SummaryThe extent of DMSP demethylation has been hypothesized to depend on DMSP availability and bacterial sulfur demand, which might lead to niche differentiation of the demethylating bacterial community. In this study, we determined DMSP concentrations in marine snow and the ambient water over a seasonal cycle and linked DMSP concentrations to the abundance of bacteria harbouring the demethylation dmdA gene in the Adriatic Sea. In marine snow, DMSP concentrations were up to four times higher than in the ambient water and three times higher in marine snow in summer than in winter. The average dmdA:recA gene ratio over the sampling period was 0.40 ± 0.24 in marine snow and 0.48 ± 0.21 in the ambient water. However, at the subclade level, differences in the demethylating bacterial community of marine snow and the ambient water were apparent. Seasonal patterns of potentially demethylating bacteria were best visible at the oligotype level. In the ambient water, the SAR116 and the OM60/NOR5 clade were composed of oligotypes that correlated to high DMSP concentrations, while oligotypes of the Rhodospirillales correlated to low DMSP concentrations. Our results revealed a pronounced seasonal variability and spatial heterogeneity in DMSP concentrations and the associated demethylating bacterial community.
Highlights
Dimethylsulfoniopropionate (DMSP) is a sulphur-containing metabolite mainly produced by marine phytoplankton in species-specific concentrations (Stefels, 2000)
The extent of DMSP demethylation has been hypothesized to depend on DMSP availability and bacterial sulfur demand, which might lead to niche differentiation of the demethylating bacterial community
Seasonal patterns of potentially demethylating bacteria were best visible at the oligotype level
Summary
Dimethylsulfoniopropionate (DMSP) is a sulphur-containing metabolite mainly produced by marine phytoplankton in species-specific concentrations (Stefels, 2000). DMSP acts primarily as an osmolyte and serves as an antioxidant, cryoprotectant or represents an overflow metabolite (Karsten et al, 1996; Malin and Erst, 1997; Stefels, 2000; Simó, 2001; Sunda et al, 2002). It is released from phytoplankton into the ambient water and is subsequently degraded by bacteria either via the DMSP cleavage or demethylation pathway (Kiene et al, 2000; Moran et al, 2012). Specific subclades of the dmdA gene, responsible for the demethylation of DMSP, have been found in different size fractions of coastal waters, suggesting that bacteria with contrasting lifestyles, such as free-living versus particle-attached, could potentially demethylate DMSP (Varaljay et al, 2010)
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