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Insights into mechanisms of high productivity and cultivation flexibility resulting from physiological and omic analyses of the microalga Marinichlorella kaistiae KAS603

Abstract

Microalgae are essential primary producers and CO2 sequesters in aquatic environments. They represent a bioenergy source in the global energy system and can be exploited as feedstock for biofuel, food supplements, vaccines, wastewater treatment, fertilizers, bioplastics, and as part of urban infrastructure in architectural designs of eco-communities. Microalgal productivity can be favored by optimizing nutrients in cultivation systems and by using environmentally flexible algal strains. Describing the potential mechanisms of high (TAG and biomass) productivity and cultivation flexibility followed by microalgal strains can improve basic phycology knowledge as well as algal management in industry. The green unicellular alga, Mk KAS603 is a strain that can thrive in freshwater, seawater and hypersalinity. With specific amounts of sodium bicarbonate, sodium acetate and sodium chloride added to cultivation systems, the strain is able to accumulate biomass and TAG. In a pilot plant, hypersalinity culturing of Mk KAS603 improves productivity mostly due to diminishing growth of invading organisms. As Mk KAS603 grows in different trophic and cultivation conditions, it changes its multiple fission reproductive mode, implicating changes in cell size, cell growth rate and mitotic rounds that is reflected in biomass and TAG accumulation. Through the combination of physiological, genomic and transcriptomic data analysis we were able to predict metabolic changes in different cell compartments in Mk KAS603 while being cultivated in different conditions. The most relevant predictions were the possible accumulation of starch in two compartments: cytoplasm and chloroplast; the possible synthesis of osmolytes (glycerol during log phase and glycine and serine during stationary phase) and the shutdown of FA beta oxidation in order to accumulate FA-TAG, in hypersalinity. Our work is aimed at providing insights into algal metabolism and productivity, and we propose that the capacity of Mk KAS603 to thrive in different cultivation and trophic environments is due to a coordinated regulation of energy and carbon flux in different cellular compartments while modifying its multiple fission division mode.

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