Abstract
Dimethylsulfoniopropionate (DMSP), a sulfur containing osmolyte and antioxidant, is suggested to take over the role of nitrogen-containing osmolytes under nitrate-depleted conditions. But other factors like time of day or limitation by nutrients can influence the cellular DMSP content as well. Especially in diatoms the complex dynamics of this central metabolite are still poorly understood. Therefore, we monitored the DMSP content in batch cultures of the diatom Skeletonema marinoi over the entire culture development, using a detailed sampling protocol on a diurnal basis to investigate the influence of the day/night cycle and limitation by nitrogen and other nutrients on cellular DMSP. Cultures were inoculated with initial high nitrate (N+) or low nitrate (N-) concentrations to evaluate the effects of nitrogen availability. The DMSP content per cell varied significantly with a 4-fold increase over the entire experiment. For N+ conditions a pronounced diurnal pattern was found with increasing DMSP contents per cell during the light and decreasing DMSP contents during the dark period. However, when DMSP was normalized to cell volume, the highest concentrations occurred near the beginning of the light period. For N- cultures no such pronounced pattern was found. DMSP values of N- cultures increased within a few hours after the medium became nitrate depleted, while no such connection between nitrogen-concentration and DMSP could be observed in the N+ cultures, where possibly an overflow mechanism or limitation of other nutrients such as Si might affect DMSP concentrations. Based on this data set we can conclude that DMSP formation in S. marinoi is under a pronounced diurnal control and depends in a rather complex manner on other factors such as growth limitation by nutrients. (C) 2011 Elsevier BY. All rights reserved.
