Influence of Cultivation Conditions on Microalgae Dunaliella Salina Resistance to Lower Temperatures

Microalgae are the perspective objects for bioeconomics, since they are the raw materials for procurement of biofuel, biologically active substances etc.In spite of the achieved successes, the task of intense cultivation and designing the ways for their efficient storage is still relevant.The precultivation at low temperatures is a mandatory stage in plant object cryopreservation.The microalgae resistance to lower temperatures and freeze-thawing depends on many factors such as: cultivation conditions, growth phase and initial concentration of cells in culture.This research was aimed to study the effect of cultivation conditions on D. salina resistance to lower temperatures depending on growth stage and population density.The D. salina culture was obtained from the microalgae collection of the Botany Chair of V.N.Karazin Kharkiv National University.Microalgae cells were cultured in Artari medium [N.Masyuk, 1973] or modified Ramaraj solution [S.Ramaraj, 2013].The concentration and motility of cells was determined with light microscope LOMO Mikmed 2.After D. salina culturing in the Artari medium within 40 days a slight cell growth was obtained.In order to optimize the D. salina culture growth and biomass accumulation we used then the Ramaraj medium.This allowed us to get a high concentration of cells already to day 10 of cultivation.The storage of culture at temperature of 3.5…4°C was associated with a decrease in cell concentration to day 10 comparing to initial amounts by 45% in average, herewith their motility in exponential and stationary growth phases was 78.5 and 100%, respectively.The findings, obtained after storage of the cell culture at 3.5…4°C within 30 days demonstrated higher resistance to lower temperatures of the cells, taking in stationary growth phase to be more resistant to lower temperatures.For example, the total number and motility of D. salina cells to day 30 of storage were 52.17 and 20.51% in exponential phase and 63 and 78.1% in a stationary growth phase.Our findings demonstrated the fact that during cell storage at lower temperatures up to 10 days the growth phase of D. salina had no significant effect on their concentration, and affected only their motility only, meanwhile the culture in the stationary growth phase was more expedient to use for longer storage (up to 30 days).