Abstract
Although acrylate has long been known to be a cleavage product of dimethylsulfoniopropionate (DMSP) by DMSP lyase, its marine cycle has been largely ignored due to analytical limitations. Dimethylsulfide (DMS) 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 equimolar quantities from DMSP cleavage. It is therefore surprising that very little is known about the production and fate of acrylate in the marine environment. Acrylate is a reactive compound that is hypothesized to be part of antiviral, antibacterial, and antioxidant systems, and as a possible grazing deterrent in seawater. It is also photochemically reactive, and acrylate is a carbon source for both anaerobic and aerobic bacteria. Therefore, acrylate is expected to significantly influence the chemistry and ecology of marine waters. A simple high performance liquid chromatography (HPLC) method was developed to quantify low to sub-nanomolar concentrations of acrylate in seawater. This method is based on the pre-column derivatization reaction of o-thiosalicylic acid with acrylate directly in water to form a highly absorbing product. By applying the method to field samples, dissolved acrylate concentrations were detected in the Gulf of Mexico in the low nanomolar range, well below previously published concentrations. Corresponding biological turnover rates of acrylate were comparable to DMS, with turnover times on the order of hours to days, and the contribution of acrylate to the biological carbon demand in the Gulf of Mexico was low. Concurrent uptake and turnover measurements of dissolved dimethylsulfoxide were quite slow, ranging from days to weeks in near surface waters. Batch cultures studies of the important harmful algal bloom species Karenia brevis indicated that cellular acrylate concentrations were constitutively high in K. brevis (ca. millimolar range), both in nutrient replete and nutrient-limited cultures. Surprisingly, dissolved acrylate made up the majority of total acrylate (76 - 97%). Combined, these results indicate a self-regulation of cellular acrylate concentrations and a mechanism for K. brevis to remove acrylate from the cell.