Ecophysiology of Deuterostichococcus epilithicus (Chlorophyta, Trebouxiophyceae), isolated from surface snow at Rhodope Mountains, Bulgaria

A green microalga of genus Deuterostichococcus (Chlorophyta, Trebouxiophyceae) strain CCALA 1137, was discovered on the surface of a temporary snow field in Bulgaria. In its natural environment, this alga must cope in two distinct habitats: cold snow in spring and warm soil in summer. This study evaluated the strain’s growth optima and limits while also employing a biotechnological approach to investigate its responses to elevated temperatures. Cultivation experiments were conducted in crossed gradients of temperature, irradiance and nutrients to determine the growth requirements of this newly identified strain. The alga was characterized as psychrotolerant, with an optimal temperature range of 14–16°C, exhibiting a preference for high irradiance and moderate nutrients for growing. Survival mechanisms at higher temperatures were examined by assessing the growth rate, biochemical composition, and efficiency of the antioxidant enzymatic defence system. The greatest biomass accumulation occurred at 17, 21 and 28°C. Though no significant differences in the quantities of cellular lipids, carbohydrates, and carotenoids were observed at these temperatures, notable variations were reported in enzyme activities. High levels of superoxide dismutase, catalase, peroxidase, and glutathione reductase were detected at 17 and 21°C, whereas these enzyme activities were lower at 28°C. A suppressed growth rate at 25°C correlated with reduced lipid and carbohydrate content in the biomass, and decreased activity of all antioxidant enzymes. These findings suggest that the alga’s observed physiological responses contribute to its tolerance and capacity to adapt to the varying conditions typical for its natural habitat.