Effect of phosphate availability on the dynamics of polyphosphate accumulation in microalgae

Phosphorus is one of the crucial elements required for the proper functioning of metabolic processes in microalgae. Despite the crucial role of phosphate (P), the dynamics of polyphosphate accumulation with respect to nutrient availability remain unknown in freshwater microalgae. We have investigated three freshwater microalgal strains - Chlorella pyrenoidosa, Scenedesmus obliquus, and Chlamydomonas reinhardtii under varied phosphate treatments to understand the phosphate metabolic responses and polyphosphate dynamics. Our results show that the accumulation of polyP in microalgae is very dynamic and mainly depends on the availability of extracellular phosphate. Reduced P availability showed algal species-specific reduction in the polyphosphate storage with a decline in growth and total chlorophyll content. Further, an increase in lipid and carbohydrate content with a substantial decrease in protein was observed under P stress, suggesting preferential utilization of stored polyP to support cell survival. Species-specific differences in the fatty acid profiles were also observed in the GC analysis among all three algal strains, indicating varied mechanisms happening among the species to adapt and protect themselves against cellular damage under P stress. Our results suggest the existence of natural variability among the selected algal strains in their ability to accumulate polyP and metabolites with respect to P-varied conditions. Among the three microalgal species, Scenedesmus obliquus showed notably enhanced accumulation of polyphosphate, highlighting its potential application as P-rich biofertilizer.