Screening for a low-cost Haematococcus pluvialis medium reveals an unexpected impact of a low N/P ratio on vegetative growth

The green alga is the current best source of natural astaxanthin, a high-value carotenoid. Traditionally, the production process of astaxanthin by this algae is achieved by a two-stage system: during the first stage, vegetative green cells are produced and then converted, in the second stage, into cysts that accumulate astaxanthin. In this work, a medium screening strategy based on the mixing of a three-component hydroponic fertilizer was applied to identify a new formulation optimized for the vegetative stage. A maximal and high cell density of 2 x 10(6) cells mL(-1) was obtained in a medium containing a high level of phosphate relative to nitrate, resulting in a N/P ratio much lower than commonly used media for . In this medium, cells remained at the vegetative and motile stage during a prolonged period of time. Both high cell density culture and motile stage persistence was proved to be related to the N/P feature of this medium. We conclude that the macrozoid stage of is favored under high-P and low-N supply and that low-cost hydroponic fertilizers can be successfully used for achieving high density cultures of vegetative cells of .