The effects of ionizing irradiation on growth and lipid production in Chlorella sorokiniana

Abstract

The impact of ionizing radiation on microalgae represents an important biotechnological and environmental issue. However, it has not been sufficiently investigated. Herein, we analyzed the effects of lowdose X-radiation on the growth, lipid production, and chlorophyll (Chl) and carotenoids content in Chlorella sorokiniana (CCAP 211/8K), which is both, a model and biotechnologically relevant species. C. sorokiniana culture was grown in 3N-BBM+V medium, at 22°C with a continuous photon flux of 120 μmol m−2 s−1. X-ray irradiation was applied in the early exponential phase of growth, at different doses (1, 2, 5, 10, 20 Gy) and rates (0.06, 0.24, 0.55 Gy/min). Parameters were monitored for 30 days. The exposure to 2 Gy and 5 Gy had a positive impact on biomass production. Dry weight was significantly higher in treated cultures than controls at days 25 and 30. Total lipid content (according to Nile Red fluorescence assay) was increased at day 30 in cultures exposed to 1 Gy (0.06 Gy/min) and 5 Gy (0.24 Gy/min). Chl content was increased for these doses in the exponential phase of growth. Chl b and carotenoids content was not significantly affected by irradiation. It is noteworthy that higher doses (10 and 20 Gy) had suppressing effects on growth and lipid production. The positive effects of ionizing radiation on biomass and lipid production can be attributed to the phenomenon of radiation hormesis (beneficial effects of low dose radiation on different biological parameters). Radiation hormesis has been shown previously documented on a number of plant species, and can be potentially employed in microalgae industry. On the other hand, microalgae are exposed to increased levels of ionizing irradiation in aquatic systems that are infested with radionuclides either naturally or by anthropogenic activity. Our results may add to the understanding of eco-physiology of microalgae in such systems.