APPLICATION OF RESPONSE SURFACE METHODOLOGY (RSM) FOR CULTURE CONDITIONS AND BIOMASS PRODUCTION OF PSYCHROPHILIC MICROALGAE ISOLATED FROM HIGH MOUNTAINS LAKE DURING THE ICE-FREE SEASON

Abstract

Many studies on cold environments have been developed over the past two decades. High mountain freshwater presents high variability of nutrients and chemico-physical parameters, showing variations of pH, oxygen concentration, metals and temperature throughout the year. National Park of Sierra Nevada (Granada, Spain) (37°032 N 03°182 W), has almost 40 lakes that are reported to be both endemic and oligotrophic. However, very little information about their microbial diversity can be found in literature. In this work, a Response Surface Methodology (RSM) was used to find best nutritional conditions for the isolation of psychrophilic microalgae from La Caldera Lake. The results showed that best culture medium, was the Rodriguez-Lopez medium (RL); data were adjusted to a quadratic prediction model reporting a biomass concentration over 600 mg/L at 10 and 20oC. In this paper, the diversity of culturable freshwater microalgae in the La Caldera Lake was observed by PCR using specific primers for eukaryotic 18S rRNA genes. Samples were taken in early July and late Agust, 2011. In July presence of strains belonging to the Eustigmatophyceae, Bacillariophyceae, Trebouxiophyceae, Chlorophyceae and Scenedesmaceae families were found. In August, only microalgae from the Eustigmatophyceae, Trebouxiophyceae, Chlorophyceae and Scenedesmaceae families were found. An individual culture of each isolated strain was carried out. Microalgae S21 had phylogenetic similitude with Chlorophyceae, and showed best growth being biomass concentration in RL 393.73 mg/L and 128.52 mg/L at 20oC and 10oC, respectively. Moreover, specific growth rates (µ max ), 0.25/h and 0.13/h at 20oC and 10oC, respectively, were detected for strain S21.