Project: RUI: Vitamin B12 and nitrogen regulation of oceanic dimethylsulfoniopropionate and dimethylsulfide

Description from NSF award abstract:
Vitamin B12 and nitrogen are nutrients critical to phytoplankton growth. Since B12 is produced solely by bacteria, phytoplankton must acquire their B12 from bacteria. Nitrogen is used to produce the amino acid methionine and B12 is required by the enzymes that form methionine. Methionine is the precursor to the algal metabolite dimethylsulfoniopropionate (DMSP). Bacteria degrade this compound to the climatically-active compound dimethylsulfide (DMS). Subsequent DMS transfer into the atmosphere is considered a significant driver of cloud formation and a possible climate feedback mechanism. DMSP can also be degraded via a secondary pathway to form methylmercaptopropionate (MMPA), which is not released to the atmosphere. Consequently, DMSP formation and the extent of DMSP degradation to DMS or MMPA are susceptible to B12 availability. Nitrogen availability influences this effect by controlling methionine production. Thus, the overarching premise for this study is that B12 availability regulates oceanic DMSP and DMS formation, and is synergistically impacted by nitrogen limitation. By providing a mechanistic understanding of relevant biogeochemical parameters this study will significantly improve the incorporation of sulfur-related microbial processes into climate models.

This project will combine established biogeochemistry-based measurements with cutting-edge metabolomics, transcriptomics and proteomics techniques in laboratory and field studies. Culture experiments will examine the interactive effect of B12 and nitrogen availability on DMSP formation in several ecologically-relevant phytoplankton taxa. Second, the microbial degradation of DMSP and DMS in relation to B12 availability will be examined using several environmentally-important bacteria and archaea. Finally, field studies will examine the seasonal variability of B12, DMSP and DMS, and the relative importance of DMS and MMPA formation in the South Atlantic Bight. Gene and protein expression will be assessed at each level of this study to identify gene products, metabolic pathways, and cellular mechanisms underlying the interconnections between B12, sulfur, and nitrogen cycles. The results generated will have a major impact on current understanding of the role of B12 and nitrogen on the DMSP and DMS cycling, as well as the potential role of these stressors in global climate change. In addition to providing evidence for microbe-based mechanisms behind the modulation of oceanic DMS, this project will (1) furnish an explanation for "summer DMS paradox", thus having significant implications for the development of future DMS models, (2) assess the interactive impact of B12 and nitrogen availability on intracellular DMSP production and (3) provide insight as to whether B12 may play a far more critical role in modulating climate feedback mechanisms on phytoplankton productivity.