For more than thirty years, oceanographers and atmospheric scientists have studied dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) because they form the basis of a biogeochemical system that transfers sulfur from the oceans to the atmosphere, affecting the Earth?s radiation balance and climate. Through these studies, we have learned that DMS and DMSP also significantly impact the ecology and chemistry of the oceans. The intensive effort to understand the marine biogeochemistry of DMS(P) has revealed that their cycling is much more complex than first imagined, but it has also caused us to largely overlook a highly interesting and important component of the DMS(P) cycle, namely acrylate, a product formed from the degradation of DMSP via DMSP lyase. Surprisingly little is known about acrylate concentrations, fluxes, or impacts in the oceans, even though concentrations and fluxes should at times be substantial, especially during blooms of DMSP-rich algae that are common throughout the world?s oceans and often harmful or toxic.
In this study, researchers at the SUNY College of Environmental Science and Forestry will conduct a three-year laboratory and field study to examine several fundamental aspects of the marine acrylate cycle. The main objectives of the proposed research are: (1) to determine the kinetics and wavelength dependence for the photolysis of acrylate in contrasting oceanic waters; (2) to determine cellular and dissolved acrylate concentrations in axenic algal cultures and evaluate how these concentrations change in response to nutrient or light stress and growth stage; and (3) to determine dissolved and particulate acrylate concentrations, photolysis rates, and biological loss rates in contrasting oceanic water through participation in two Gulf of Mexico research cruises.
Broader Impacts: Results from this study are expected to significantly improve our fundamental understanding of the marine acrylate cycle and its impact on the biogeochemistry of the upper oceans. The project will establish and foster research and educational collaborations for these students, especially the graduate students, through several avenues including participation at national and local meetings, mentoring, preparing for and delivering college-level lectures, and presentations made to the general public at forums such as Syracuse?s Milton J. Rubenstein Museum of Science. Two graduate students and a visiting Chinese scholar will be trained as part of this project, along with several undergraduates. Finally, the PI will participate in several activities to promote and foster education including serving as an NSF STEM mentor, co-coordinating Chemistry Day at the NY State Fair, giving oral presentations at local K-12 schools, and mentoring SUNY ESF Environmental Science and Chemistry students.
A wide range of algae in the oceans contain copious quantities of the compound dimethylsulphoniopropionate (DMSP). The DMSP-containing algae include nearly all harmful algal bloom (HAB) species that are responsible for massive toxic blooms that occur in coastal waters throughout the world. Remarkably, in many of these algae, DMSP constitutes a disproportionately large percentage (up to 20%) of the total carbon content. For many algae, DMSP can be enzymatically degraded to dimethylsulfide (DMS) and acrylate. The sulfur-containing compounds, DMS and DMSP, have been studied intensively for over 30 years owing to the potential importance of DMS in indirectly regulating the Earth’s climate. Investigations into ocean-atmosphere cycling of DMS has led to a greater understanding about the marine sulfur cycle as it relates to the production of DMS and related compounds including DMSP and dimethylsulfoxide (DMSO). Dimethylsulfide and DMSP concentrations can be high during marine algal blooms, and acrylate concentrations are expected to be high as well, since DMS and acrylate are produced in equal amounts from the enzymatic degradation of DMSP. It is therefore very surprising that virtually nothing is known about the production and fate of acrylate in the marine environment. Acrylate is a reactive compound that scientists hypothesize to be part of antiviral, antibacterial, and antioxidant systems. Acrylate may also be produced by algae to provide protection against grazing, and acrylate is a carbon source for both anaerobic and aerobic bacteria. Acrylate also degrades in seawater when exposed to sunlight. Thus, acrylate is expected to significantly influence the chemistry and ecology in sunlit oceanic waters, but up to now there has been little supportive evidence. One key limitation has been the lack of a sensitive method to measure acrylate in seawater. We developed an extremely sensitive method to measure acrylate in seawater that is from one to four orders of magnitude more sensitive compared to published techniques. We used our newly developed method to investigate fundamental aspects of the marine acrylate cycle including field studies to determine: (1) acrylate concentrations in the Delaware Estuary and Gulf of Mexico in both coastal and open-ocean waters; (2) rates of biological uptake of acrylate as a source of carbon for energy and growth; and (3) degradation rates of acrylate in seawater samples that were exposed to sunlight. We also conducted a laboratory study to determine: (1) particulate and dissolved acrylate concentrations in relation to DMSP and DMSO during the growth of several common marine algal species including Karenia brevis, Thalassiosira pseudonana, Procentrum minimum and Phaeocystis antarctica; and (2) the effects of nutrient limitation on the growth and chemical composition (DMSP and acrylate) of the HAB species K. brevis. Several surprising discoveries were made as a result of this field and lab study. Acrylate and DMSP comprised up to 2 and 10% of the total amount of carbon in the algae examined in this study. This finding is remarkable given that acrylate is a well-known toxicant in cellular systems, but clearly it is not toxic to these marine algae. At high concentrations in algae, acrylate (and DMSP) will serve as an antioxidant, and it is unlikely that algae will regulate concentrations of acrylate (or DMSP) for this function. Even though there is a lot of acrylate associated with algal cells, in all species of algae that were studied, more than half of the acrylate and nearly all the DMSO were present in the dissolved phase and not in the algae, indicating that acrylate should be an important compound fueling the growth of the microbial community in seawater during blooms of DMSP-containing algae such as the Prymnesiophyceae (e.g., P. antarctica and E. huxleyi) and many of the HAB species (e.g., , Karenia brevis, a common bloom-forming dinoflagellate in the Gulf of Mexico and other subtropical and temperate coastal waters), since these bloom-forming species should excrete large quantities of acrylate into the surrounding seawater. Indeed, in the Gulf of Mexico field study, we found that acrylate was readily used by microbes for energy and growth . Although this work has provided some invaluable information regarding the marine acrylate cycle, much research is still needed. Further investigations into the marine acrylate cycle are needed to elucidate why acrylate is produced and to determine the environmental fate and functions of this compound in marine waters.
