Effects of light intensity on the production of phycoerythrin and polyunsaturated fatty acid by microalga Rhodomonas salina

Abstract

Phycoerythrin (PE) is a phycobiliprotein with great potential in food, pharmaceuticals, and cosmetics applications. This work sought to investigate the effects of lighting conditions on the PE synthesis by the alga Rhodomonas salina. It was found that the effects of light intensity on the cell growth and PE synthesis highly depend on the cell density, and ultimately, the number of photons received per unit of cells. No obvious light limitation or inhibition to cell growth was observed when each cell received the photons within the range of 2.4–28 × 10−9 μmol·s−1. Under low light intensity, R. salina increased the PE synthesis in order to capture more photons to compensate light deficiency. A strategy of stepwise increasing light intensity was developed to capture the rapid cell growth and high PE synthesis. The PE titer with this method reached 32 mg L−1, ~20% higher than that obtained at a fixed light intensity of 250 μmol photon flux m−2 s−1 (μmol·m−2·s−1). In addition to PE synthesis, R. salina also produces an appreciable amount of omega-3 polyunsaturated fatty acids (PUFAs) with stearidonic acid (SDA, C18:4) in particular. Collectively, this work demonstrates that light intensity plays an important role in the culture of R. salina for simultaneous production of PE and PUFAs.