Determination of total and particulate dimethylsulfoniopropionate (DMSP) concentrations in four scleractinian coral species: A comparison of methods

Coral dinoflagellate symbionts (zooxanthellae) are known to produce the multifaceted sulfur compound dimethylsulfoniopropionate (DMSP) but its role in coral symbioses remains obscure. As methods for quantifying DMSP from isolated symbionts or intact symbioses are not standardized, the aim of this study was to improve DMSP measurements in these fields. We focused on issues pertaining to the separation of host and symbiont, multiple DMSP extraction techniques and several normalization indices in four reef building coral species. Measurements of total DMSP (coral and zooxanthellae; DMSPt) and particulate DMSP (zooxanthellae; DMSPp) levels were made in Montastraea cavernosa, Madracis mirabilis, Montastraea franksi and Porites asteroides together with common DMSP indices including, chlorophyll-a, zooxanthellae number/size, total protein, coral surface area and polyp number. Several potential preparation methods for quantifying DMSPt and/or DMSPp were investigated; coral fragments placed directly in MeOH and airbrushed coral homogenates placed in either methanol (MeOH) or sodium hydroxide (NaOH). DMSP values varied among the corals and according to the type of normalization indice used, which was limited by the chosen preparation method. DMSPt was most efficiently recovered from coral homogenates extracted in MeOH. Additionally, for two of the four coral species, DMSPp was highest in homogenates extracted in MeOH. All corals had higher DMSPt than DMSPp concentrations (typically 2–3×) when analyzed using the same preparation method, suggesting that DMSP may be translocated from symbiont to host thus highlighting the need for both DMSPp and DMSPt measures to fully understand the physiological significance of this DMSP partitioning in corals. These results suggest that DMSPt and DMSPp in previously frozen, field-collected corals is best quantified by placing the airbrushed coral tissue homogenate in MeOH and subsequently measuring DMS via headspace analysis after the addition of strong base and sufficient equilibration time.