Strategies of phosphorus utilization in an astaxanthin-producing green alga Haematococcus pluvialis, a comparison with a bloom-forming cyanobacterium Microcystis wesenbergii

Haematococcus pluvialis is a unicellular green alga with great commercial value, due to its synthesis of powerful antioxidant astaxanthin. H. pluvialis was mainly distributed in small water bodies but was also observed in eutrophicated lakes, and even coexisted with Microcystis. However, Haematococcus cells never prevail in eutrophicated water bodies. Phosphorus is the main limiting factor in most aquatic ecosystems and may have a role in the distribution of H. pluvialis. Here, we focused on the physiological responses of H. pluvialis to various phosphorus conditions (0.002, 0.02, 0.2, and 2 mM), and compared with a bloom-forming cyanobacterium Microcystis wesenbergii. Growth determination suggested that high phosphorus conditions (0.2 mM and 2 mM) favor the growth of H. pluvialis cells, but H. pluvialis cells have a shorter duration of log phase than M. wesenbergii cells. Growth determination also indicated H. pluvialis cells had lower tolerability to low phosphorus (0.002 mM). Qualitative comparisons from long-term and short-term phosphorus uptake experiments, polyphosphate accumulation and extracellular alkaline phosphatase expression analysis suggested two different phosphorus utilization strategies in the two species. H. pluvialis cells were characterized with the induction of extracellular alkaline phosphatase to survive phosphorus-deficient condition, while M. wesenbergii cells were characterized with quick uptake of phosphorus and accumulation more of polyphosphate in phosphorus-replete conditions. To our knowledge, this is the first study to demonstrate features of phosphorus uptake and utilization in H. pluvialis, which will increase our understanding in the distribution of H. pluvialis.