Effect of the diel cycle on production of dimethylsulfoniopropionate in batch cultures of Emiliania huxleyi.

International audienceChanges in intracellular DMSP, nitrogen, carbon, chlorophyll a, total cell volume, and cell numbers were measured during day and night in axenic, exponentially growing batch cultures of Emiliania huxleyi cultured at 20o C under a 12h:12h light:dark cycle. Cellular DMSP content in the cultures increased at a specific rate of 0.80 ± 0.10 d-1 during the day and 0.53 ± 0.12 d-1 at night. By contrast, cellular carbon and Chl a content of the culture and total cell volume increased only during the day and showed no significant change at night. Cellular nitrogen content of the culture showed a much higher specific rate of increase during the day than at night. Because intracellular DMSP had a lower specific rate of synthesis during the day and a higher specific rate at night than specific production rates for the various cell “biomass” parameters (total cell volume, and cell carbon, nitrogen, and Chl a), ratios of DMSP to these parameters were highest at the end of the dark period and decreased during the day. The maximum in intracellular DMSP concentrations at the beginning of the light period may provide some level of protection from oxidative stress with the daytime initiation of photosynthesis. Significant intracellular production of DMSP during the night contradicts current “conventional wisdom”, which assumes no night time biosynthesis of DMSP. Previous calculations based on this invalid assumption will need to be reassessed