Effect of increased CO2 on dimethylsulfoniopropionate (DMSP) lyase activity in the coccolithophorid Emiliania huxleyi
Emiliania huxleyi is an important component of the global carbon and sulfur cycles, yet little is known about the potential impacts of increasing pCO2, particularly on the relevant dimethylsulfoniopropionate (DMSP) lyase enzyme. DMSP lyase activity (DLA) was measured on a transect during the North Atlantic spring bloom in June 2005. DLA was quantified using gas chromatography and found to vary from 0 ‚Äì 26.35 nmol L-1 min-1. No significant hydrographic trends were found, however, DLA was generally highest near the surface and decreased with depth. Phytoplankton pigment analysis suggested that coccolithophorids were a large source of the DLA. A shipboard continuous culture experiment analyzed the effects of pCO2 and temperature in a two by two pCO2 (380, 750 ppm)/temperature (12 ¬∫C, 16 ¬∫C) matrix. Various parameters were significantly increased by either high temperature or high pCO2. A significant temperature/CO2 interaction was found with DLA, but there were no differences with normalized DLA. Biomass normalized DMSP was significantly increased at high temperature. A laboratory based semi-continuous culture experiment analyzed the effect of pCO2 (150, 350, 750 ppm) on E. huxleyi (non-calcifier). Cell density was significantly higher in the 750 ppm treatment in the first two dilutions, and in the third dilution cell density was significantly higher in the 150 ppm treatment. This suggests an inhibitory effect at high pCO2 due to acidification. There were no treatment differences with cell normalized DMSP or DLA, which were highest at the time of dilution and decreased over the growth cycle. Light levels within the cultures decreased with growth. Our results are consistent with the accepted idea that DLA may be involved in oxidative stress protection, particularly at high light levels, but further investigations are warranted to improve our understanding of DMSP-lyase in coccolithophorids.