Use of exogenous glycine betaine and its precursor choline as osmoprotectants in Antarctic sea‐ice diatoms¹

Abstract

Wide salinity ranges experienced during the seasonal freeze and melt of sea ice likely constrain many biological processes. Microorganisms generally protect against fluctuating salinities through the uptake, production, and release of compatible solutes. Little is known, however, about the use or fate of glycine betaine (GBT hereafter), one of the most common compatible solutes, in sea‐ice diatoms confronted with shifts in salinity. We quantified intracellular concentrations and used [14C]‐labeled compounds to track the uptake and fate of the nitrogen‐containing osmolyte GBT and its precursor choline in three Antarctic sea‐ice diatoms Nitzschia lecointei, Navicula cf. perminuta, and Fragilariopsis cylindrus at −1°C. Experiments show that these diatoms have effective transporters for GBT, but take up lesser amounts of choline. Neither compound was respired. Uptake of GBT protected cells against hyperosmotic shock and corresponded with reduced production of extracellular polysaccharides in N. lecointei cells, which released 85% of the retained GBT following hypoosmotic shock. The ability of sea‐ice diatoms to rapidly scavenge and release compatible solutes is likely an important strategy for survival during steep fluctuations in salinity. The release and recycling of compatible solutes may play an important role in algal–bacterial interactions and nitrogen cycling within the semi‐enclosed brines of sea ice.

Environmental factors influencing the seasonal dynamics of spring algal blooms in and beneath sea ice in western Baffin Bay

“…In 2015, bulk ice nutrient concentrations correlated with ice algal biomass (TChla 0-3cm ; r [NO 3 -+NO 2 -] = 0.8; r [PO 4 3-] = 0.74, r [Si(OH) 4 ] = 0.47; p < 10 -3 ) and showed elevated concentrations in the ice bottom relative to those in the interface water, suggesting that a nutrient ' concentration mechanism' was at play in sea ice. Similar observations have been made previously and have been suggested to be associated with a release of intracellular pools due to osmotic shock during ice melt processing (Cota et al, 1990(Cota et al, , 2009Harrison et al, 1990;Pineault et al, 2013;Torstensson et al, 2019) or via production of biofilms by sea ice diatoms and bacteria that potentially trap nutrients (Krembs et al, 2002(Krembs et al, , 2011Steele et al, 2014). Bacterial activity may also have played a role through nutrient remineralization (Fripiat et al 2014(Fripiat et al , 2017Firth et al, 2016).…”

Elevated temperature and decreased salinity both affect the biochemical composition of the Antarctic sea-ice diatom Nitzschia lecointei, but not increased pCO2

“…(Pal et al 2011). It is also possible that cell lysis from the hypoosmotic shock may have overestimated cellular lipid and MDA content, if particlebound lipids from cell debris are collected on the filters for TBARS and fatty acid analysis, similar to the way other macromolecules are retained on 0.2 µm filters after lysis with H 2 SO 4 (Torstensson et al 2019).…”

“…Extracellular polysaccharide substances (EPS) are carbonrich compounds produced by microorganisms and play an important role in sea-ice environments (Deming and Young 2017). Yields of EPS have been reported to increase in seaice diatoms when grown at elevated salinity and decreased temperature, and are therefore believed to act as important osmo-and cryoprotectant (Aslam et al 2012;Torstensson et al 2019). The cryoprotective properties of EPS may explain why the carbohydrate content of N. lecointei was higher at −1.8 °C compared to 3 °C in the present study.…”

Enhanced bottom-ice algal biomass across a tidal strait in the Kitikmeot Sea of the Canadian Arctic

“…In this study the concentration of NO 3 + NO 2 in the bottom ice fell closer to the salinity dilution line derived from average surface water nutrient concentrations (Figure 5a), further supporting the potential for nitrogen depletion relative to that of PO 4 or Si(OH) 4 that were well above it. The elevated concentrations of PO 4 and Si(OH) 4 in the ice bottom relative to those in the interface water suggest that algae were potentially retaining excess quantities as intracellular pools that were leaked into the bulk ice measurement due to osmotic shock during melt Harrison et al, 1990;Smith et al, 1990;Pineault et al, 2013;Campbell et al, 2016;Torstensson et al, 2019). Another explanation is that sea ice diatoms and bacteria produce copious amounts of exopolymeric substances that can increase viscosity and reduce diffusion, as well as adsorption of some ions, potentially trapping nutrients within a sea ice biofilm (Krembs et al, 2002(Krembs et al, , 2011Steele et al, 2014;Roukaerts, 2018).…”