Luxury phosphorus uptake in microalgae

Phosphorus (P) is central to storing and exchange of energy and information in cells including those of microalgae. The overwhelming majority of microalgae are naturally acclimated to low-P environments; hence, they are capable of taking up and storing P in large amounts whenever it becomes available. The ability to take up more P than necessary for immediate growth is termed “luxury uptake.” Understanding this phenomenon constitutes a crucial insight into nutrient-driven processes in natural algal communities such as harmful algal blooms, as well as into the operation of algae-based technologies for sustainable usage of P such as recycling of the nutrient from wastewater to biofertilizers. The bulk of P acquired during luxury uptake is stored in the form of inorganic polyphosphate, the compound with nearly ubiquitous presence and multifaceted function in the cell. Although seminal works on luxury P uptake and polyphosphate metabolism were carried out fifty years ago, application of modern “omics” approaches and advanced imaging microscopy techniques enabled obtaining a deeper mechanistic insight into these processes. Nevertheless, our knowledge about luxury P uptake remains much more limited in comparison with that about P shortage and mechanism tolerance to this stress in microalgae. In this review the knowledge of luxury P uptake originating from classical phycological and biochemical methods is confronted with the recently obtained understanding of molecular mechanisms of P transport to the cell, polyphosphate biosynthesis, regulation, and genetic control of these processes. Biotechnological implications of the knowledge about luxury P uptake accumulated to date are discussed in the context of algae-based approaches to sustained usage of nutrients and industrial cultivation of microalgae.