Seasonal dynamics of marine snow‐associated and free‐living demethylating bacterial communities in the coastal northern Adriatic Sea

9 pages, 5 figures, supporting information https://doi.org/10.1111/1758-2229.12783

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. 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

This study was funded by the Wittgenstein prize (Austrian Science Fund, FWF, Z194‐B1) to G.J.H. and the projects ARTEMIS (P28781‐B21) and DK microbial nitrogen cycling (W1257‐B20) to G.J.H. The Spanish MINECO also provided funding through project BIOGAPS (CTM2016‐81008‐R) to R.S. Financial support was also provided by the Ministry of Science and Education, Croatia through the project ‘Role of marine snow on planktonic system in the northern Adriatic’ and by the Croatian Science Foundation through project UIP‐2014‐09‐6563 (Phytoplankton life strategies in the northern Adriatic) to D.M.P. and I.I. This work is in partial fulfilment of the requirements for a Ph.D. degree from the University of Vienna to P.A.S.

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