The proteome of Chlamydomonas reinhardtii during phosphorus depletion and repletion

Algae can efficiently harvest phosphorus (P) and store this nutrient as intracellular polyphosphates (polyPs), an ability of industrial potential, such as P-removal during wastewater treatment. However, a better understanding of P metabolism is first needed before P-removal and recovery can be reliably engineered by triggering polyPs synthesis. The proteomic response of Chlamydomonas reinhardtii was therefore studied, for the first time, during growth under different condition of P availability. For this purpose, five biological replicates (controls) were grown on low P media for 18 days while five biological replicates (treatments) were grown under similar conditions until day 11, when they then received 10 mg-P center dot L (-1). In the P-repleted treatments, the rapid increase in cellular P content (%P up to 2.14 g-P center dot g-DW (-1)) and granular polyP abundance evidenced an overplus response. Comparative analysis of the proteomes of P-repleted and P-depleted cultures evidenced P-depletion was associated with an increase in the abundance of proteins involved in P assimilation and storage, including polyP synthesis. Hence these cells were ready to rapidly uptake P and intracellularly accumulate polyP upon Prepletion, as verified experimentally. In contrast, P-repletion was associated with an increase in the abundance of proteins involved in ribosome structure and synthesis, and translation, but a decrease in the abundance of proteins associated with P assimilation and storage. Our findings corroborate, for the first time, data from past transcriptomics studies of P-related genes and therefore suggests that the transcriptomic and proteomic responses of P-related genes and proteins are synchronized in C. reinhardtii. These findings unify observations from independent past studies on C. reinhardtii and other microalgae species, suggesting a common evolution of P metabolism (including polyP synthesis) in microalgae. Importantly, the data also suggests that post-translational regulation of the vacuolar transport chaperone subunits control polyP synthesis in C. reinhardtii (rather than transcriptional regulation).