Application of structural, functional, fluorescent, and cytometric indicators for assessing physiological state of marine diatoms under different light growth conditions

Authors: NATALIA SHOMAN, EKATERINA SOLOMONOVA, ARKADII AKIMOV

Abstract: The changes in the main structural, functional, fluorescent, and cytometric indicators of diatom microalgae Phaeodactylum tricornutum (Bohlin, 1897), sp., and Skeletonema costatum (Cleve, 1873) under different light growth conditions were analyzed; the potential of their application as possible indicators for monitoring algae physiological state was evaluated. For all studied species, uniform light dependences of specific growth rate, C/Chl a, coefficient of cell size variability, relative variable chlorophyll a fluorescence (Fv/Fm), FDA fluorescence, and ratio of living cells were obtained. A significant correlation was established between Fv/Fm and C/Chl a in algae cells. As shown, Fv/Fm indicator is ineffective for diagnosing changes in algae growth characteristics, when changing light conditions. Under optimal light conditions, the ratio of living cells in a population is at least 75%, and cell size variability (CV) is below 30%. In turn, a decrease in the ratio of living cells and an increase in CV correlate with a decrease in algae specific growth rate and an increase in C/Chl a in their cells under photoinhibition. The practicability of using FDA fluorescence and the ratio of living cells in unicellular algae cultures to assess a lethal effect of external factors on algae structural and functional characteristics is shown, since a drop in values of the described indicators is observed at extreme values of the light factor, which are lethal or close to them.

Keywords: Microalgae, light intensity, flow cytometry, specific growth rate, C/Chl a, relative variable chlorophyll a fluorescence, FDA fluorescence, ratio of living cells, cell size variability

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