Award: OCE-1436458

The major goals of this project fell into two main categories: 1) the first major goal is to elucidate the impact of vitamin B12 and nitrate availability of the production of the algal osmolyte dimethylsulfoniopropionate (DMSP) in several model phytoplankton species using a combination of traditional biogeochemistry and molecular biology approaches along with state-of-the-art transcriptomics and metabolomics techniques. 2) the second major goal is to examine the impact of vitamin B12 and nitrate availability of the production of DMSP in mixed phytoplankton communities from two contrasting environments, namely coastal/shelf waters and oligotrophic open-ocean waters. To address the first goal, a series of laboratory experiments was conducted to examine the short-term impact of nitrogen and vitamin B12 deprivation on DMSP formation in 3 contrasting model phytoplankton species, namely the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana, and the coccolithophorid Emiliania huxleyi (CCMP 374). These species were selected because they possess differing abilities to handle nutrient limitation. The results of the experiments revealed that short term (< 96 hours) vitamin B12 deprivation had no effect on the major osmolytes and RNA transcripts examined in each of the model species. Conversely, the analyses revealed significant changes to the major osmolytes, namely increases in intracellular DMSP, and RNA transcripts in response to nitrogen limitation over the same time period. These findings will have important implications for our understanding of the cellular-level responses of these organisms and modelling the formation of DMSP. To address the second goal, a series of field experiments was carried out during the expeditions in the South Atlantic Bight to examine the short-term impact (< 48 hours) of nitrogen and Vitamin B12 additions on DMSP and DMS formation in natural marine microbial communities. Surface seawater for the incubation experiments was collected at a (mid-shelf) coastal site near Gray?s Reef, Georgia USA, and at an offshore oligotrophic site in the Sargasso Sea. Throughout the course of the field experiments, vitamin B12 had little or no effect on DMSP levels associated with particles, DMSP dissolved in the seawater or DMS in the seawater. Since the experimental communities were not axenic, which provided a natural source of vitamin B12 for the phytoplankton component of the microbial community, they do not appear to have been B12‑limited or co-limited. In general, DMSPp concentrations increased immediately upon the addition of nitrate but appeared to be caused by increased phytoplankton biomass (Chlorophyll a )rather than increased biosynthesis of DMSP by the phytoplankton (as measured by DMSPp:Chl a ratios). Moreover, since the experiments were conducted on a relatively short time scale (2 days), the observed changes in DMSPp:Chl a ratios were unlikely to have been caused by shifts in the taxonomic composition of the phytoplankton community. The most plausible explanations are an increase in Chl a levels and a decrease in DMSP levels resulting from an alleviation of oxidative stress caused by nitrogen limitation. These findings will have important implications for the development of biogeochemical modeling of DMSP and DMS in the global sulfur cycle. This grant has provided direct financial support, training and/or resources for 4 undergraduate students, 2 College of Charleston Honors College students and 6 graduate students: Last Modified: 09/24/2020 Submitted by: Peter A Lee