Effect of gamma irradiation on the growth and lipid productivity of green microalgae

In the present research, the impact of exposing cultures of Chlamydomonas sp., Scenedesmus ecornis, and S. communis microalgae to doses of gamma-rays (γ-ray) on their growth and the productivity of lipids was investigated. Biomass concentration (g L-1) of each microalga was periodically determined after exposure to a range of gamma irradiation doses of 0, 25, 50, 75, 100, 200, and 300 Gray (Gy) through 20 days of cultivation period. Then, the lipid content (%) and lipid productivity (mg L-1 day-1) of each species were also evaluated. Obtained results indicated that the S. ecornis growth was positively affected by gamma irradiation, that the maximum concentration of biomass was obtained after 15 days at 1.32 g L-1 by the irradiated S. ecornis exposed to a dose of 300 Gy while the non-irradiated culture achieved up to 1.10 g L-1. On the other hand, the growths of Chlamydomonas sp. and S. communis were significantly reduced by gamma irradiation treatment also significant variations have also been observed in the levels of lipid content and lipid productivity of each microalga. Irradiated S. ecornis at a dose of 300 Gy exhibited the maximum of lipid content percentage and lipid productivity to reach 28.4% and 24.9 mg L-1 day-1, respectively. Conversely, the best yields of lipid content and lipid productivity were achieved by a non-irradiated culture of S. communis (24.4% and 16.6 mg L-1 day-1, respectively), compared to irradiated culture, regardless of irradiation dose. The highest lipid content and lipid productivity gained by Chlamydomonas sp. were obtained by the cultures exposed to 25 Gy, being 27.3% and 21.3 mg L-1 day-1, respectively. In conclusion, results indicated that exposing cells of S. ecornis and Chlamydomonas sp. to specific doses of γ-rays has significantly stimulated lipid accumulation in cells, unlike S. communis which was negatively affected by gamma irradiation.