ИСТИНА

Microalgae are believed to evolve under conditions of scarce and fluctuating availability of phosphorus (P). Adaptations to P shortage include rearrangements of lipid metabolism and polar metabolome, downregulation of photosynthetic activity, and luxury uptake of P. The latter is defined as taking up more P that necessary for the progression of current cell cycle. Luxury uptake of P is the basis of the nutrient conversion from waste streams to phosphorus biofertilizers. The mechanisms of microalgaе acclimation to P starvation are relatively well studied, but luxury uptake of P remains enigmatic in many regards. Phosphorus starvation induces smaller penalties for the culture growth e.g. in comparison with those of nitrogen starvation since nutrient-replete microalgal cells normally possesses a sizeable reserve of P, frequently in the form of inorganic polyphosphates which are created during the periods of luxury P uptake. Nevertheless, high concentrations of exogenic P can be toxic resulting in the inhibition of microalgal cell division or even death which can be a concern for wastewater biotreatment with microalgal cultures. We hypothesize that P toxicity arises when the rate of P uptake is much faster than its conversion into long-chain polyphosphate coupled with their transport into the cell vacuole(s). Instead of this, a lot of short-chain polyphosphate molecules chaotically distributed in the cytoplasm are formed disturbing with protein folding. This can be the case during re-feeding of P-starved cultures with large amounts of P. Understanding the relationships between P availability, cell viability and capacity for P uptake is essential for the development of efficient knowledge-based microalgal biotechnologies both for valuable substance production and protection of the environment.