Abstract
Using a mathematical simulation approach, we studied the dynamics of the green microalga Chlorella vulgaris phosphate metabolism response to shortage and subsequent replenishing of inorganic phosphate in the medium. A three-pool interaction model was used to describe the phosphate uptake from the medium, its incorporation into the cell organic compounds, its storage in the form of polyphosphates, and culture growth. The model comprises a system of ordinary differential equations. The distribution of phosphorous between cell pools was examined for three different stages of the experiment: growth in phosphate-rich medium, incubation in phosphate-free medium, and phosphate addition to the phosphorus-starving culture. Mathematical modeling offers two possible scenarios for the appearance of the peak of polyphosphates (PolyP). The first scenario explains the accumulation of PolyP by activation of the processes of its synthesis, and the decline in PolyP is due to its redistribution between dividing cells during growth. The second scenario includes a hysteretic mechanism for the regulation of PolyP hydrolysis, depending on the intracellular content of inorganic phosphate. The new model of the dynamics of P pools in the cell allows one to better understand the phenomena taking place during P starvation and re-feeding of the P-starved microalgal cultures with inorganic phosphate such as transient PolyP accumulation. Biotechnological implications of the observed dynamics of the polyphosphate pool of the microalgal cell are considered. An approach enhancing the microalgae-based wastewater treatment method based on these scenarios is proposed.
Highlights
In nature, microalgae frequently encounter the stress caused by the lack of mineral nutrients such as nitrogen, phosphorus (P), and sulfur, the key constituents of amino acids, proteins, lipids, photosynthetic pigments, vitamins, and other vital compounds
To describe the experimental kinetics, we took the existing phosphate interaction model (PIM) [11] and exPIM [10] models, in which PolyP is synthesized from inorganic phosphate
Since it is known that ATP and other phosphorylated molecules are involved in the synthesis and hydrolysis of PolyP, we assumed that phosphate fluxes in the cell should be described differently, namely, that the PolyP is synthesized from organic
Summary
Microalgae frequently encounter the stress caused by the lack of mineral nutrients such as nitrogen, phosphorus (P), and sulfur, the key constituents of amino acids, proteins, lipids, photosynthetic pigments, vitamins, and other vital compounds. This stress profoundly affects the physiological condition of the microalgal cells. During their evolution, microalgae have developed various adaptations for coping with the nutrient depletion in their natural habitats. P-starving cells of microalgae and cyanobacteria accumulate polyphosphates (PolyP) at an increased rate after replenishing phosphate in their growth medium [5,6,7]. This metabolic feature elicited a keen interest of researchers for many years since it opens new possibilities for wastewater treatment with microalgae, on the one hand, and using the resulting algal biomass enriched with P as a fertilizer, on the other hand [8,9]
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