Abstract
Marine anthozoans maintain a mutualistic symbiosis with dinoflagellates that are prolific producers of the algal secondary metabolite dimethylsulfoniopropionate (DMSP), the precursor of the climate-cooling trace gas dimethyl sulfide (DMS). Surprisingly, little is known about the physiological role of DMSP in anthozoans and the environmental factors that regulate its production. Here, we assessed the potential functional role of DMSP as an antioxidant and determined how future increases in seawater pCO2 may affect DMSP concentrations in the anemone Anemonia viridis along a natural pCO2 gradient at the island of Vulcano, Italy. There was no significant difference in zooxanthellae genotype and characteristics (density of zooxanthellae, and chlorophyll a) as well as protein concentrations between anemones from three stations along the gradient, V1 (3232 μatm CO2), V2 (682 μatm) and control (463 μatm), which indicated that A. viridis can acclimate to various seawater pCO2. In contrast, DMSP concentrations in anemones from stations V1 (33.23 ± 8.30 fmol cell−1) and V2 (34.78 ± 8.69 fmol cell−1) were about 35% lower than concentrations in tentacles from the control station (51.85 ± 12.96 fmol cell−1). Furthermore, low tissue concentrations of DMSP coincided with low activities of the antioxidant enzyme superoxide dismutase (SOD). Superoxide dismutase activity for both host (7.84 ± 1.37 U·mg−1 protein) and zooxanthellae (2.84 ± 0.41 U·mg−1 protein) at V1 was 40% lower than at the control station (host: 13.19 ± 1.42; zooxanthellae: 4.72 ± 0.57 U·mg−1 protein). Our results provide insight into coastal DMSP production under predicted environmental change and support the function of DMSP as an antioxidant in symbiotic anthozoans.
Highlights
Dimethylsulfoniopropionate (DMSP) is a secondary metabolite that is produced and accumulated at high intracellular concentrations by many microalgae (Keller et al 1989) including members of the dinoflagellates (Caruana et al 2012)
Anemones of all three stations were associated with symbionts of Symbiodinum type A19. pCO2 had a significant effect on DMSPt concentrations in the tentacles of A. viridis both when normalized to cell (F2, 45 = 6.47, P = 0.028; Fig. 2A) and to protein (F2, 45 = 13.96, P = 0.000; Fig. 2B)
Irrespective of normalization indices, DMSPt concentrations from the control station were about 35% higher (51.85 Æ 6.26 fmol cellÀ1 or 172.12 Æ 10.13 nmolÁmgÀ1 protein; equivalent to 6.49 Æ 0.19 lmolÁgÀ1 fresh weight (FW)) than concentrations in tentacles from stations V1 (33.23 Æ 8.30 fmol cellÀ1 or 121.72 Æ 7.05 nmolÁmgÀ1 protein; equivalent to 3.95 Æ 0.25 lmolÁgÀ1 FW) and V2 (34.78 Æ 8.69 fmol cellÀ1 or 114.51 Æ 7.69 nmolÁmgÀ1 protein; equivalent to 4.54 Æ 0.18 lmolÁgÀ1 FW)
Summary
Dimethylsulfoniopropionate (DMSP) is a secondary metabolite that is produced and accumulated at high intracellular concentrations (typically hundreds of mmol LÀ1) by many microalgae (Keller et al 1989) including members of the dinoflagellates (Caruana et al 2012). It is the precursor of dimethylsulfide (DMS), the main natural source of reduced sulfur released to the atmosphere (Bates et al 1987; Kettle and Andreae 2000). High levels of atmospheric CO2 continue to increase aqueous pCO2 and result in the concomitant decrease in seawater pH
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