Ecophysiological, morphological, and biochemical traits of free-living Diplosphaera chodatii (Trebouxiophyceae) reveal adaptation to harsh environmental conditions

Abstract

Single-celled green algae within the Trebouxiophyceae (Chlorophyta) are typical components of terrestrial habitats, which often exhibit harsh environmental conditions for these microorganisms. This study provides a detailed overview of the ecophysiological, biochemical, and ultrastructural traits of an alga living on tree bark. The alga was isolated from a cypress tree in the Botanical Garden of Innsbruck (Austria) and identified by morphology and molecular phylogeny as Diplosphaera chodatii. Transmission electron microscopy after high-pressure freezing (HPF) showed an excellent preservation of the ultrastructure. The cell wall was bilayered with a smooth inner layer and an outer layer of polysaccharides with a fuzzy hair-like appearance that could possibly act as cell-cell adhesion mechanism and hence as a structural precursor supporting biofilm formation together with the mucilage observed occasionally. The photosynthetic-irradiance curves of D. chodatii indicated low light requirements without photoinhibition at high photon flux densities (1580 μmol photons m−2 s−1) supported by growth rate measurements. D. chodatii showed a high desiccation tolerance, as 85% of its initial value was recovered after controlled desiccation at a relative humidity of ~10%. The alga contained the low molecular weight carbohydrates sucrose and sorbitol, which probably act as protective compounds against desiccation. In addition, a new but chemically not elucidated mycosporine-like amino acid was detected with a molecular mass of 332 g mol−1 and an absorption maximum of 324 nm. The presented data provide various traits which contribute to a better understanding of the adaptive mechanisms of D. chodatii to terrestrial habitats.

A chemosystematic investigation of selected <italic>Stichococcus</italic>-like organisms (Trebouxiophyta)

“…However, the combination of sorbitol + sucrose may be consistent within the genera studied. A recent work by Medwed et al (2021) also shows that Diplosphaera produces sorbitol + sucrose during growth. These findings support the phylogenetic exclusion of the algal strain SAG 48.41 from the Stichococcus-like genera, as it does not produce sorbitol.…”

“…The NMR spectra were recorded with a Bruker spectrometer ( 1 H: 500.13 MHz; 13 C: 125.8 MHz, AVANCE 500 Neo spectrometer (Bruker BioSpin, Ettlingen, Germany). Chemical shifts δ are given in ppm relative to the signal for internal est: the presence of low molecular weight carbohydrates (LMWC) has both consequences for the cell biology and physiology in terms of osmotic stress tolerance (Roberts 2005, Holzinger and Karsten 2013, Holzinger and Pichrtová 2016 and has been demonstrated to be a stable taxonomic character (Gustavs et al 2011, Darienko et al 2015, Hotter et al 2018. It also provides valuable information on the ecophysiology of the strains, which is usually missing from classical phylogenetic analyses.…”

“…This cooperation would not have been possible without the generous materials support from Dr. Anna Temraleeva (Algal Collection of Soil Science Institute, Puschchino, Russia), Dr. Pavel Škaloud (Charles University, Prague, Czech Republic), Dr. Lira Gaysina (Resource Centre Culture Collection of Microorganisms, St. Petersburg, bust 1980, Darienko et al 2015. However, the combination of sorbitol + sucrose may be consistent within the genera studied.…”

The Ecophysiological Performance and Traits of Genera within the Stichococcus-like Clade (Trebouxiophyceae) under Matric and Osmotic Stress

“…Other studies in Trebouxiophyceaen algae present on tree bark showed that they, as one biofilm unit, are able to survive and recover after being exposed to extended drought periods of up to 80 days [35]. This was reiterated in [58], where a Diplosphaera chodatii isolate collected from tree bark reached nearly 100% initial Y(II) after being exposed to water for post-dehydration, albeit after a far shorter desiccation period (45 min at 10% RH).…”

“…It was not until beyond this time that there was an appreciable uptick overall. Medwed [58] and Karsten [32] showed recovery that reached a plateau at~190 and~1000 min, respectively, so it is possible that the Stichococcus-like strains needed slightly longer to reach peak recovery.…”