ИСТИНА

It is believed that the overwhelming majority of microalgal species evolved 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. All these adaptations are exploited in microalgal biotechnology. Thus, nutrient starvation induces accumulation of valuable carotenoids and lipids in the microalgal cells whereas luxury uptake is the basis of conversion of the nutrients from waste streams to phosphorus biofertilizers from microalgal biomass. 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.