AUTHOR=Liu Jingli , Liu Ji , Zhang Sheng-Hui , Liang Jinchang , Lin Heyu , Song Delei , Yang Gui-Peng , Todd Jonathan D. , Zhang Xiao-Hua 

TITLE=Novel Insights Into Bacterial Dimethylsulfoniopropionate Catabolism in the East China Sea

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.03206

DOI=10.3389/fmicb.2018.03206

ISSN=1664-302X

ABSTRACT=<p>The compatible solute dimethylsulfoniopropionate (DMSP), made by many marine organisms, is one of Earth's most abundant organosulfur molecules. Many marine bacteria import DMSP and can degrade it as a source of carbon and/or sulfur via DMSP cleavage or DMSP demethylation pathways, which can generate the climate active gases dimethyl sulfide (DMS) or methanthiol (MeSH), respectively. Here we used culture-dependent and -independent methods to study bacteria catabolizing DMSP in the East China Sea (ECS). Of bacterial isolates, 42.11% showed DMSP-dependent DMS (Ddd<sup>+</sup>) activity, and 12.28% produced detectable levels of MeSH. Interestingly, although most Ddd<sup>+</sup> isolates were <italic>Alphaproteobacteria</italic> (mainly Roseobacters), many gram-positive <italic>Actinobacteria</italic> were also shown to cleave DMSP producing DMS. The mechanism by which these <italic>Actinobacteria</italic> cleave DMSP is unknown, since no known functional <italic>ddd</italic> genes have been identified in genome sequences of Ddd<sup>+</sup><italic>Microbacterium</italic> and <italic>Agrococcus</italic> isolates or in any other sequenced <italic>Actinobacteria</italic> genomes. Gene probes to the DMSP demethylation gene <italic>dmdA</italic> and the DMSP lyase gene <italic>dddP</italic> demonstrated that these DMSP-degrading genes are abundant and widely distributed in ECS seawaters. <italic>dmdA</italic> was present in relatively high proportions in both surface (19.53% ± 6.70%) and bottom seawater bacteria (16.00% ± 8.73%). In contrast, <italic>dddP</italic> abundance positively correlated with chlorophyll <italic>a</italic>, and gradually decreased with the distance from land, which implies that the bacterial DMSP lyase gene <italic>dddP</italic> might be from bacterial groups that closely associate with phytoplankton. Bacterial community analysis showed positive correlations between <italic>Rhodobacteraceae</italic> abundance and concentrations of DMS and DMSP, further confirming the link between this abundant bacterial class and the environmental DMSP cycling.</p>