Effects of environmental factors on dimethylated sulfur compounds and their potential role in the antioxidant system of the coral holobiont

Abstract

Biogenic dimethylsulfide (DMS) and its main precursors, dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO), are potential scavengers of reactive oxygen species in marine algae, and these dimethylated sulfur compounds (DSC) could take part in the algal antioxidant system. In this study, a link between the DSC production and the antioxidant capacity (AOC) of Acropora aspera reef coral was investigated under a range of environmental factors (temperature, light, salinity, and air exposure) that can lead to oxidative stress in the coral holobiont. Enhanced DMS(P)(O) production occurred under experimental conditions, indicating that DSC are potential biomarkers of stress level in coral tissue. Differences in concentrations and partitioning as a response to different treatments suggest that DSC production and turnover undergo different biochemical pathways depending on the type and severity of environmental stress. Osmotic pressure and light depletion led to an upregulation of the coral AOC that was correlated with a significant increase in DMSO : DSC ratio. These results, combined with a positive correlation between the AOC and DMSO concentrations under these two treatments, suggest that the DMSP-based antioxidant system is involved in the overall antioxidant regulation of the coral holobiont. Enhanced DMS production coupled with an increased DMS : DSC ratio under increased temperature indicated that thermal stress triggers DMS formation in coral tissue. Considering the role that DMS can have in both climate regulation and the DMSP-based antioxidant system, our findings highlight the need to further examine the fate of DSC in coral reef environments under scenarios of increasing sea surface temperatures.

Dimethylsulfoniopropionate, superoxide dismutase and glutathione as stress response indicators in three corals under short-term hyposalinity stress

“…In contrast, S. pistillata and P. damicornis showed no regulation of DMSP with changing salinity, suggesting it was less effective in regulating the corals osmotic potential, as indicated by the greater physiological stress. With respect to its role in oxidative stress, increased DMSP production is usually associated with increased ROS levels in Symbiodinium [6,21,29]. The lack of upregulation of DMSP production, irrespective of the increased antioxidant activity measured here, suggests that the corals primary response to hyposaline conditions was to reduce its osmotic potential.…”

“…Furthermore, given that DMSP is energetically expensive to produce [55], if cellular activity of the coral is reduced or compromised, de novo synthesis of DMSP may have been limited. The formation of DMSO constitutes an additional shield against oxidative stress, because it can be further oxidized in the presence of ROS [21], and as such, it has been suggested to be an effective biomarker of stress exposure in corals [29]. Evidence for the use of DMSP as an antioxidant through the increased conversion of DMSP to DMSO was also only apparent in A. millepora, resulting in an increased ratio of DMSO : DMSP (figure 4g).…”

“…It has also been suggested to form an antiviral defence mechanism [18] and most recently has been shown to act as a trigger for dinoflagellate parasitoid activation [19]. However, following the work of Sunda et al [20], over the past decade, there has been a strong interest in the role DMSP may play in alleviating cellular oxidative stress [5,6,20,21] and the biochemical processes thought to be involved with coral bleaching and antioxidant quenching from DMSP explored [22].…”

“…Upon reacting with ROS, DMS and DMSP are oxidized to form DMSO. Therefore, if the DMSP-based antioxidant system were to have a significant role as an antioxidant under increased oxidative stress, DMSO should increase [21], meaning DMSP can be a very sensitive indicator of coral stress [29].…”

Dimethylsulfoniopropionate in corals and its interrelations with bacterial assemblages in coral surface mucus

“…[26] Most importantly, DMSP and its enzymatic breakdown products, DMS, acrylate, dimethylsulfoxide (DMSO) and methane sulfinic acid (MSNA), are scavengers of hydroxyl radicals and other reactive oxygen species (ROS) in marine algae. [27] Hypothesised as an antioxidant also in coral symbioses, [28] DMSP is therefore ecologically relevant because it may help corals to survive conditions of thermal stress, [7] and because it likely plays a major role in structuring coral-associated bacterial communities. [21] Both phenomena might have significant consequences at the ecosystem level.…”