Effect of PAR irradiance intensity on Phaeocystis antarctica (Prymnesiophyceae) growth and DMSP, DMSO, and acrylate concentrations

Abstract

Phaeocystis antarctica forms extensive spring blooms in the Southern Ocean that coincide with high concentrations of dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), dimethylsulfide (DMS), and acrylate. We determined how concentrations of these compounds changed during the growth of axenic P. antarctica cultures exposed to light‐limiting, sub‐saturating, and saturating PAR irradiances. Cellular DMSP concentrations per liter cell volume (CV) ranged between 199 and 403 mmol · LCV−1, with the highest concentrations observed under light‐limiting PAR. Cellular acrylate concentrations did not change appreciably with a change in irradiance level or growth, ranging between 18 and 45 mmol · LCV−1, constituting an estimated 0.2%–2.8% of cellular carbon. Both dissolved acrylate and DMSO increased substantially with irradiance during exponential growth on a per‐cell basis, ranging from 0.91 to 3.15 and 0.24 to 1.39 fmol · cell−1, respectively, indicating substantial export of these compounds into the dissolved phase. Average cellular DMSO:DMSP ratios increased 7.6‐fold between exponential and stationary phases of batch growth, with a 3‐ to 13‐fold increase in cellular DMSO likely formed from abiotic reactions of DMSP and DMS with reactive oxygen species (ROS). At mM levels, cellular DMSP and acrylate are proposed to serve as de facto antioxidants in P. antarctica not regulated by oxidative stress or changes in ROS. Instead, cellular DMSP concentrations are likely controlled by other physiological processes including an overflow mechanism to remove excess carbon via acrylate, DMS, and DMSO during times of unbalanced growth brought on by physical stress or nutrient limitation. Together, these compounds should aid P. antarctica in adapting to a range of PAR irradiances by maintaining cellular functions and reducing oxidative stress.

Diel variation of seawater volatile organic compounds, DMSP-related compounds, and microbial plankton inside and outside a tropical coral reef ecosystem

“…This lends support to the hypothesis that DMS is produced by and released from planktonic and benthic microalgal cells (including coral-associated Symbiodiniaceae) in response to high irradiance or due to its antioxidant properties (Sunda et al, 2002;Slezak et al, 2007;Galıé t al., 2013a, Galı́et al, 2013bLawson et al, 2021;Masdeu-Navarro et al, 2022). Alternatively, the energy of midday incident radiation can easily exceed the photosynthetic electron transport capacity, conditions under which DMSP can be released, as such or upon transformation into DMS, as a strategy to dissipate excess energy (Stefels, 2000;Kinsey et al, 2023). The hypotheses of oxidative stress and excess energy dissipation are not mutually exclusive, and support to the latter is given by the fact that DMDS (hence MeSH) behaved the same as DMS (positive Spearman's correlation, Figure 6A), suggesting DMSP release by phytoplankton as well as corals (Masdeu-Navarro et al, 2022) and rapid bacterial degradation to DMS, acrylate d and MeSH.…”