CONCENTRATIONS OF DIMETHYLSULFONIOPROPIONATE AND DIMETHYL SULFIDE ARE STRAIN-SPECIFIC IN SYMBIOTIC DINOFLAGELLATES ( SYMBIODINIUM SP., DINOPHYCEAE) 1 Michael Steinke, 2 Patrick Brading, Philip Kerrison University of Essex, Department of Biological Sciences, Coral Reef Research Unit, Wivenhoe Park, Colchester CO4 3SQ, UK Mark E. Warner College of Earth, Ocean, and Environment, University of Delaware, 700 Pilottown Road, Lewes, Delaware 19958, USA and David J. Suggett University of Essex, Department of Biological Sciences, Coral Reef Research Unit, Wivenhoe Park, Colchester CO4 3SQ, UK Dimethyl sulfide (DMS) and dimethylsulfoniopro- pionate (DMSP) are sulfur compounds that may function as antioxidants in algae. Symbiotic dinofla- gellates of the genus Symbiodinium show strain-speci- fic differences in their susceptibility to temperature- induced oxidative stress and have been shown to contain high concentrations of DMSP. We investi- gated continuous cultures of four strains from dis- tinct phylotypes (A1, A13, A2, and B1) that can be characterized by differential thermal tolerances. We hypothesized that strains with high thermal toler- ance have higher concentrations of DMSP and DMS in comparison to strains with low thermal tolerance. DMSP concentrations were strain-specific with highest concentrations occurring in A1 (225 ± 3.5 mmol Æ L )1 cell volume [CV]) and lowest in A2 (158 ± 3.8 mmol Æ L )1 CV). Both strains have high thermal tolerance. Strains with low thermal tolerance (A13 and B1) showed DMSP concentrations in between these extremes (194 ± 19.0 and 160 ± 6.1 mmol Æ L )1 CV, respectively). DMS data further confirmed this general pattern with high DMS concentrations in A1 and A13 (4.1 ± 1.22 and 2.1 ± 0.37 mmol Æ L )1 CV, respec- tively) and low DMS concentrations in A2 and B1 (0.3 ± 0.06 and 0.5 ± 0.22 mmol Æ L )1 CV, respec- tively). Hence, the strain-specific differences in DMSP and DMS concentrations did not match the different abilities of the four phylotypes to withstand thermal stress. Future work should quantify the possible dynamics in DMSP and DMS concentrations during periods of high oxidative stress in Symbiodinium sp. and address the role of these antioxidants in zooxan- thellate cnidarians. Key index words: continuous culture; dimethyl sul- fide (DMS); dimethylsulfoniopropionate (DMSP); strain specificity; Symbiodinium Abbreviations: DMS, dimethyl sulfide; DMSP, di- methylsulfoniopropionate The marine trace gas DMS is important for the global biogeochemical cycling of sulfur, since it facilitates the transfer of this element from the oceans to the continents (Stefels et al. 2007). In the atmosphere, it can provide precursors for the pro- duction of cloud condensation nuclei that enhance cloud formation and, hence, affect climate (Charl- son et al. 1987, Vallina and Simo ´ 2007). The vast majority of DMS is produced from the secondary algal metabolite DMSP via various enzymatic path- ways in bacteria (Todd et al. 2007, Curson et al. 2008), fungi (Todd et al. 2009), and algae (Steinke et al. 1998). The exact cellular function of both compounds is still uncertain, but four, not mutually exclusive, possibilities are most widely discussed: (i) DMSP has a role as an osmolyte and compatible solute that protects cellular metabolism under osmotic stress (Kirst 1996). (ii) DMSP and DMS may be involved in an activated grazing defense mecha- nism (Wolfe et al. 1997) and mediate trophic inter- actions (Steinke et al. 2002, DeBose et al. 2008). (iii) Stefels (2000) describes the role of DMSP bio- synthesis in an overflow mechanism under unba- lanced algal growth that regenerates nitrogen for protein metabolism in algae (overflow hypothesis). (iv) Sunda et al. (2002) suggest that the often highly abundant DMSP can efficiently quench reac- tive oxygen species (ROS) but that the potential as antioxidant is greatly increased after the rapid enzy- matic conversion to DMS and acrylate. This latter mechanism predicts that DMSP turnover is high when cells are exposed to increased levels of ROS. The average concentrations of DMS and DMSP are typically in the low nM range in offshore sea- water (Kettle et al. 1999) and in waters surround- ing coral reefs (Jones et al. 2007). In contrast, 1 Received 21 December 2009. Accepted 14 January 2011. 2 Author for correspondence: e-mail msteinke@essex.ac.uk. J. Phycol. 47, 775–783 (2011) Ó 2011 Phycological Society of America DOI: 10.1111/j.1529-8817.2011.01011.x 775