Ecophysiological Features of Polar Soil Unicellular Microalgae¹

Abstract

Due to their ecological, physiological, and molecular adaptations to low and varying temperatures, as well as varying seasonal irradiances, polar non‐marine eukaryotic microalgae could be suitable for low‐temperature biotechnology. Adaptations include the synthesis of compounds from different metabolic pathways that protect them against stress. Production of biological compounds and various biotechnological applications, for instance, water treatment technology, are of interest to humans. To select prospective strains for future low‐temperature biotechnology in polar regions, temperature and irradiance of growth requirements (Q10 and Ea of 10 polar soil unicellular strains) were evaluated. In terms of temperature, three groups of strains were recognized: (i) cold‐preferring where temperature optima ranged between 10.1 and 18.4°C, growth rate 0.252 and 0.344 · d−1, (ii) cold‐ and warm‐tolerating with optima above 10°C and growth rate 0.162–0.341 · d−1, and (iii) warm‐preferring temperatures above 20°C and growth rate 0.249–0.357 · d−1. Their light requirements were low. Mean values Q10 for specific growth rate ranged from 0.7 to 3.1. The lowest Ea values were observed on cold‐preferring and the highest in the warm‐preferring strains. One strain from each temperature group was selected for PN and RD measurements. The PN:RD ratio of the warm‐preferring strains was less affected by temperature similarly as Q10 and Ea. For future biotechnological applications, the strains with broad temperature tolerance (i.e., the group of cold‐ and warm‐tolerating and warm‐preferring strains) will be most useful.

Metabolite Profiling in Green Microalgae with Varying Degrees of Desiccation Tolerance

“…Assessing the ecophysiological performance of D. epiphytica and E. mirabilis revealed differences between the two species in light and temperature requirements for growth, and in their tolerance of desiccation. Edaphochlorella mirabilis grew better than D. epiphytica in response to increasing irradiation and temperature ( Figure 1 ), in agreement with the capability to grow under a relatively broad temperature range reported for E. mirabilis extracted from polar soil [ 21 ]. Furthermore, gross oxygen production increased with temperature up to 35 °C in E. mirabilis and to 25 °C in D. epiphytica ( Figure 2 ).…”

“…Furthermore, molecular markers of the lichen photobiont, D. chodatii , were used to study dispersal modes of the semi-aquatic lichen, Dermatocarpon luridum [ 20 ]. Comparably little is known for Edaphochlorella spp., e.g., ecophysiological studies were conducted with arctic strains [ 21 , 22 ]. In summary, some reports on the ecophysiological characteristics of Diplopshpaera and Edaphochlorella species exist, but hardly any information is available on changes in metabolism in response to environmental stress factors.…”

Annual Cycle of Mat‐Forming Filamentous Alga Tribonema cf. minus (Stramenopiles, Xanthophyceae) in Hydro‐Terrestrial Habitats in the High Arctic Revealed By Multiparameter Fluorescent Staining

“…Polar soil unicellular algae were also able to grow at low irradiances, with optimum irradiance between ~15 to 20 µmol photons ⋅ m −2 ⋅ s −1 , thus indicating an adaptation to low‐light conditions in the soil (Shukla et al. 2020).…”

“…In alpine soil algae, the saturation irradiances of photosynthesis vary around 20-40 µmol photons ⋅ m À2 ⋅ s À1 Holzinger 2012, Karsten et al 2013). Polar soil unicellular algae were also able to grow at low irradiances, with optimum irradiance between~15 to 20 µmol photons ⋅ m À2 ⋅ s À1 , thus indicating an adaptation to low-light conditions in the soil (Shukla et al 2020).…”

“…The ability to photosynthesize at extreme low irradiances, with compensation irradiances similar to those of Tribonema fonticolum and Tribonema monochloron (14.3 and 3.75 µmol photons ⋅ m À2 ⋅ s À1 , respectively; Machov a et al 2008), could be beneficial during snow melt in the spring, in which the algae could start photosynthesizing even under snow cover. Since the light attenuation in snow is approximately 0.1-10% depending on snow depth (Gorton et al 2001), and the diel maxima may reach even 1500 µmol photons ⋅ m À2 ⋅ s À1 on a sunny midday, the estimated PAR values of 1.5 -150 µmol photons ⋅ m À2 ⋅ s À1 could correspond to light intensities encountered by soil (Karsten and Holzinger 2012, Karsten et al 2013, Shukla et al 2020) and ice (Cota 1985, Rivkin and Putt 1987, Ban et al 2006) algae. In alpine soil algae, the saturation irradiances of photosynthesis vary around 20-40 µmol photons ⋅ m À2 ⋅ s À1 Holzinger 2012, Karsten et al 2013).…”