Study of three Scenedesmaceae strains: morphology, molecular phylogeny, growth and carotenogenesis.

We studied the morphology, molecular phylogeny, growth, and carotenogenesis of three Scenedesmaceae strains (IBSS-12, IBSS-109 and IBSS-112), grown in two-stage batch culture for 18 days. During the "green" stage, cells grew in favorable conditions, whereas during the "red" stage they were exposed to abiotic stresses. Morphological and molecular analyses showed that strains IBSS-12 and IBSS-109 belong to the genus Coelastrella, and strain IBSS-112 was identified as Desmodesmus. At the "green" stage, the maximum cell number was recorded in Desmodesmus (IBSS-112) on day 7, and was twice as high compared to that of Coelastrella strains. All strains showed an almost twofold increase in cell volume and significant dry biomass accumulation (1.5-1.8 g L). An increase in the carotenoid to chlorophyll ratio (by 1.5-2 times) on day 9, was a signal for switching to the "red" stage. Stress conditions caused massive cell death in Desmodesmus IBSS-112, while Coelastrella strains showed a threefold increase in cell number to the end of the experiment. The dry weight increased by 4 and 2.5 times in IBSS-12 and IBSS-109, respectively. The dry biomass productivity for the entire experimental period was 0.32 and 0.25 g L day in IBSS-12 and IBSS-109, respectively. Pigment analysis revealed typical patterns in green carotenogenic microalgae, with both Coelastrella strains acquiring a bright orange colour and increasing their carotenoid content. IBSS-12 had twice the amount of carotenoids as IBSS-109 did. Carotenoid profiles of Coelastrella strains included valuable ketocarotenoids with a predominance of astaxanthin, canthaxanthin and adonixanthin (19-26, 14-15 and 12-14% in total carotenoids, respectively). The obtained morpho-physiological and biochemical characteristics of the studied strains can serve as additional taxonomic criteria.