Abstract
Dimethyl sulfide (DMS) is an important component of the global sulfur cycle as it is the most abundant sulfur compound that is emitted via the ocean surface to the atmosphere. Dimethylsulfoniopropionate (DMSP), the precursor of DMS, is mainly produced by phytoplankton and is degraded by marine bacteria. To reveal the role of bacteria in the regulation of DMSP degradation and DMS production, mesocosm and field studies were performed in the Sanriku Coast on the Pacific Ocean in northeast Japan. The responsible bacteria for the transformation of DMSP to DMS and the assimilation of DMSP were monitored, and the genes encoding DMSP lyase (dddD and dddP) and DMSP demethylase (dmdA) were analyzed. The mesocosm study showed that the dmdA subclade D was the dominant DMSP degradation gene in the free-living (FL) and particle-associated (PA) fractions. The dddD gene was found in higher abundance than the dddP gene in all the tested samples. Most importantly, DMS concentration was positively correlated with the abundance of the dddD gene. These results indicated that bacteria possessing dmdA and dddD genes were the major contributors to the DMSP degradation and DMS production, respectively. The genes dmdA subclade D and dddP were abundant in the Tsugaru Warm (TW) Current, while the dmdA subclade C/2 and dddD genes were dominant in the Oyashio (OY) Current. Functional gene network analysis also showed that the DMSP degradation genes were divided into OY and TW Current-related modules, and genes sharing similar functions were clustered in the same module. Our data suggest that environmental fluctuations resulted in habitat filtering and niche partitioning of bacteria possessing DMSP degradation genes. Overall, our findings provide novel insights into the distribution and abundance of DMSP degradation genes in a coastal region with different water current systems.
Highlights
Dimethylsulfoniopropionate (DMSP) is mainly produced by marine phytoplankton and macroalgae as an osmolyte (Pichereau et al, 1998) and is an essential sulfur source for microbes in the seawater (Kiene et al, 1999)
Field samples were collected in different seasons (1) to identify the major DMSP degraders and dimethyl sulfide (DMS) producers in relation to different water masses of the Sanriku Coast, (2) to explore the drivers of distribution and abundance of DMSP degradation genes, and (3) to uncover functional gene networks among different DMSP degradation genes
Biophysicochemical Factors in Two Mesocosm Systems The Chl a, DMSPp, DMSPd, and DMS concentrations as well as the bacterial abundance showed resemblance between the duplicated mesocosm tanks, while these factors varied in the different mesocosm groups (Figure 2)
Summary
Dimethylsulfoniopropionate (DMSP) is mainly produced by marine phytoplankton and macroalgae as an osmolyte (Pichereau et al, 1998) and is an essential sulfur source for microbes in the seawater (Kiene et al, 1999) Once it is released into seawater, dissolved DMSP (DMSPd) mainly undergoes two different metabolic pathways mediated by bacteria (demethylation and cleavage pathways) (Curson et al, 2011; Moran et al, 2012; Figure 1). A large portion of DMS will be utilized or catabolized by marine bacteria (Boden et al, 2010; Schafer et al, 2010), while the remaining DMS is released into the atmosphere (Lovelock et al, 1972) This sea-toair DMS flux represents about 50% of the global biogenic sulfur flux (Andreae, 1990). It is essential to identify the factors that regulate the activity of DMSP-degrading bacteria in order to fully understand the global sulfur cycles
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