UV-A promotes long-term carotenoid production of Dunaliella in photobioreactors with retention of cell viability

Abstract

The effect of adding UV-A radiations (320-400 nm) to photosynthetically active radiation (PAR, 400-700 nm) during the growth of Dunaliella bardawil in an air-fluidized bed photobioreactor was studied to evaluate cell growth and long-term production of carotenoids. The obtained results were compared to those obtained from D. bardawil cultures incubated under lab standard conditions for carotenoid production, this is to say, nitrogen starvation and absence of UV-A radiation. The addition of 26.5 μmol photons m-2 s-1 UV-A radiation to 1150 μmol photons m-2 s-1 PAR stimulated the growth of D. bardawil cultures grown in a full nutrient culture medium. The total carotenoid content, mostly β-carotene, was higher than that of control cultures (UV-A non added cultures) along the exponential phase. The concentration of β-carotene in UV-A added cultures after 450 h was found to be about two-fold that of control cultures. From the results of this work it can be concluded that the UV-A modulated addition to PAR could be successfully applied to long-term carotenoid production processes, whereas D. bardawil cells accumulates carotenoids with retention of its viability. It is also shown that UV-A promotes increases of both carotenoid production per culture volume unit and the specific carotenoid production rate (pg.cell-1), β-carotene being the major accumulated carotenoid.