Morphological and morphometrical features in Dunaliella salina (Chlamydomonadales, Dunaliellaceae) during the two-phase cultivation mode

Abstract

The paper presents studies of morphological and morphometrical characteristics of green halophilic carotenogenic microalga Dunaliella salina (Dunal) Teodoresco, 1905, from the south-west region of Crimean Peninsula. D. salina was cultivated in two-phase mode under conditions of natural illumination at the premises of A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS (IBSS), Sevastopol, Russia. The maximum D. salina cell density was 1.69·106 cell/ml in the "green" phase and 0.84·106 cell/ml in the "red" growth phase. The maximum productivity by cell number reached 0.15 · 106 cell/(ml·day) in the "green" phase while it was lower by 73% in the "red" phase (0.04·106 cell/(ml·day). Along with the maximum productivity, linear growth stage in the first phase was characterized by a maximum fraction of small (up to 500 μm3 in volume) cells (about 15-29%) and a decrease in cell volume by 40-45% as compared with initial value. The mean of D. salina cell volume in the "red" phase was 30% higher than in the "green" phase. At the same time, the large cell fraction in the "red" phase was consistently high (15-35%). The patterns of change in morphological and morphometrical cell parameters were in accordance to stage and conditions of growth. Thus, cell elongation was noted in the stage of linear growth, while under unfavorable conditions at growth-declining stage cells became more round-shaped, with orange and tile-red coloration and granulation of cell content. It was shown that morphological and morphometric cell parameters can serve as additional criteria for assessment of physiological condition in D. salina culture. The experiment demonstrated the prospects for two-stage D. salina cultivation in Crimea.