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

Abstract

Changes in intracellular dimethylsulfoniopropionate (DMSP), nitrogen, carbon, chlorophyll a (chl a), total cell volume and cell numbers were measured during day and night in axenic, exponentially growing batch cultures of the coccolithophorid, Emiliania huxleyi, cultured at 20°C under a 12 h light:12 h dark cycle. Cellular DMSP content in the cultures increased at a specific rate of 0.80 ± 0,10 d -1 (mean ± SE) 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 (at specific rates of 1.30 ± 0.08 d -1 , 1.54 ± 0.12 d -1 and 1.39 ± 0.12 d -1 , respectively). Cellular nitrogen content of the culture showed a much higher specific rate of increase during the day (1.07 ± 0.07 d -1 ) than at night (0.22 ± 0.03 d -1 ). 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 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 that no nighttime biosynthesis of DMSP occurs. Previous calculations based on this invalid assumption will need to be reassessed.