Response of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas to salinity and temperature shifts in the sea-ice diatom Fragilariopsis cylindrus

Abstract

Sea ice is an extreme environment known to host microbial communities which produce high concentrations of the metabolites dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO). These two compounds are involved in the cycling of the climate cooling gas dimethylsulfide (DMS). Despite decades of research, the drivers of these large concentrations in sea ice remain largely unknown. In this study, we use a cell culture approach to quantify for the first time the DMSP and DMSO cell quotas for the diatom Fragilariopsis cylindrus under combined shifts of temperature and salinity typically encountered in the sea ice brine habitat. In doing so, we investigate two suggested potential metabolic functions for DMSP and DMSO: osmoregulation and cryoprotection. We observed an increase of both DMSP:Chl-a and DMSO:Chl-a in multiple experiments with salinities of 75 and 100 at constant temperature, which suggest osmoregulation for both compounds in the diatom cell. Stronger salinity shifts to 150 induced lethal osmotic shock resulting in massive cell death. Interestingly, combining salinity shifts with temperature shifts (as low as-7.4°C) did not modify drastically the DMSP and DMSO cell quotas, which may indicate that the cryoprotectant function of DMSP and DMSO in our diatom cultures was not-relevant. Also, decreasing the salinity to 20 at constant temperature suggested no cellular adaptation in terms of DMSP and DMSO cell quotas.

Dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas variations arising from sea ice shifts of salinity and temperature in the Prymnesiophyceae Phaeocystis antarctica

“…Also, we preferred the experiment at S75 and -2.4°C to the one at S75 and 4°C to obtain the conditions closest to those encountered by algae in situ. Whatever the temperature, results obtained at S75 were similar for both algae (Fig.3 and Wittek et al (2020)).…”

“…In this simplistic approach, we postulated that the taxonomic composition in sea ice was restricted to two major groups: diatoms and flagellates (including Phaeocystis sp., dinoflagellates and other flagellates). Hence, for our calculation, we considered that the production of DMSP and DMSO by the group of diatoms could be estimated through the empirical relations from our experiment on F.cylindrus (Wittek et al 2020) and the DSC production of flagellates by the P.antarctica empirical relations (this study).…”

“…From this study ( Fig.3) and (Wittek et al 2020), we computed empiric relations between DMSPp and DMSOp cell quotas and brine salinity for P.antarctica and F.cylindrus (Fig.4) using data from experiments conducted at S20 and 4°C, S34 and 4°C and S75 and -2.4°C. Experiments at S100 and S150…”

Enhancing Salt Tolerance of Plants: From Metabolic Reprogramming to Exogenous Chemical Treatments and Molecular Approaches

“…In another study conducted in N. tabacum plants, short-term and low-dose SS induced metabolic shifts toward gluconeogenesis, which involved accumulation of mainly glucose, sucrose and fructose with depletion of pyrimidine and purine metabolites, while a high-dose of salt increased the accumulation of the osmolytes proline, myo-inositol and GABA [ 61 ]. Dimethylsulfoniopropionate (DMSP) is produced by a large diversity of macroalgae [ 110 ] and has a significant impact on SS and temperature shifts [ 111 , 112 ]. Intracellular functions of DMSP are not well understood but this molecule has been proposed to act as an osmoregulator [ 113 ] and antioxidant [ 114 ].…”

“…These results suggested that DMSP and DMSO might play a role in SS responses and help F . cylindrus to counterattack increased salinity levels [ 112 ]. The above studies and the additional studies detailed in Table 1 demonstrate that reprogramming of PMs in plants are an adaptive response for survival under SS.…”