Glycine Betaine and Ectoine Are the Major Compatible Solutes Used by Four Different Halophilic Heterotrophic Ciliates

Abstract

One decisive factor controlling the distribution of organisms in their natural habitats is the cellular response to environmental factors. Compared to prokaryotes, our knowledge about salt adaptation strategies of microbial eukaryotes is very limited. We, here, used a recently introduced approach (implementing proton nuclear magnetic resonance spectroscopy) to investigate the presence of compatible solutes in halophilic, heterotrophic ciliates. Therefore, we isolated four ciliates from solar salterns, which were identified as Cyclidium glaucoma, Euplotes sp., Fabrea salina, and Pseudocohnilembus persalinus based on their 18S rRNA gene signatures and electron microscopy. The results of H-NMR spectroscopy revealed that all four ciliates employ the "low-salt-in" strategy by accumulating glycine betaine and ectoine as main osmoprotectants. We recorded a linear increase of these compatible solutes with increasing salinity of the external medium. Ectoine in particular stands out as its use as compatible solute was thought to be exclusive to prokaryotes. However, our findings and those recently made on two other heterotroph species call for a re-evaluation of this notion. The observation of varying relative proportions of compatible solutes within the four ciliates points to slight differences in haloadaptive strategies by regulatory action of the ciliates. Based on this finding, we provide an explanatory hypothesis for the distribution of protistan diversity along salinity gradients.

Intracellular osmoprotectant concentrations determine Propionibacterium freudenreichii survival during drying

“…Previous studies clearly evidence accumulation of osmoprotectants as a result of osmotic stress, triggering osmoadaptation (Kets et al 1996;Cardoso et al 2007;Dalmasso et al 2012;Huang et al 2016c). The accumulated osmoprotectants were analyzed by NMR as described by Behrends et al (2011), Pleitner et al (2012, Vaidya et al (2018), and Weinisch et al (2019). During osmoadaptation, P. freudenreichii is able to accumulate glycine betaine, trehalose, and glutamate, as already reported (Huang et al 2016c;Gaucher et al 2019).…”

A fundamental difference between macrobiota and microbial eukaryotes: protistan plankton has a species maximum in the freshwater‐marine transition zone of the Baltic Sea

“…Such solutes reduce the difference between the intracellular and extracellular osmotic potential, therefore, minimizing water loss and maintaining the essential cell turgor pressure (Yancey et al ., ). The compatible solute strategy might provide a physiological explanation for the salinity boundary at 10 psu, as most of the halophilic protists found to use this strategy had their lower salinity tolerance at this salinity level (Weinisch et al ., ,b). In our study, especially dictyochophytes and dinoflagellates were remarkably influenced by salinity shifts, leading to a notable species turnover and selection at salinities below 10 psu.…”

Perspectives from Ten Years of Protist Studies by High‐Throughput Metabarcoding

“…To explore these possibilities, ciliate cultures, ion imaging, and proton nuclear magnetic resonance spectroscopy were used to investigate two main haloadaptive strategies in ciliates, that is, intracellular accumulation of inorganic ions and accumulation/synthesis of compatible solutes as osmoprotectants (Weinisch et al. ,b). In agreement with the metabarcode‐based transition boundaries, experimentation indicated that ciliates exhibit different salt tolerances and that all the tested species use compatible solutes to combat osmotic stress.…”

“…Compatible solute concentrations also showed a linear increase with increasing external salinity, while the proportions of compatible solutes within each ciliate pointed at slight differences in haloadaptive strategies by regulatory actions (Weinisch et al. ,b). These and other studies that identify novel osmoprotectant chemicals (e.g.…”