Effects of additional Mg2+ on the growth, lipid production, and fatty acid composition of Monoraphidium sp. FXY-10 under different culture conditions

Abstract

The effects of supplementing the culture medium with Mg2+ on the growth, lipid production, and fatty acid composition of Monoraphidium sp. FXY-10 were studied under photoautotrophic, heterotrophic, and mixotrophic conditions. Under the photoautotrophic condition, microalgae supplemented with 100 μM Mg2+ grew significantly better than the control group and exhibited a secondary growth state. The final cell density was 1.25-fold higher than that of the control group (2.98 g L−1), and the peak lipid content reached 59.8 % (control group 52.3 %). Culture under the heterotrophic condition did not significantly increase the growth rate, but the experimental group (100 μM Mg2+ supplementation) achieved a 37.03 % lipid content compared to 28.47 % by the control group. The lipid productivity of the experimental group (100 μM Mg2+ supplementation) was higher, reaching 65.93 mg L−1 day−1 compared with 56.10 mg L−1 day−1 for the group without additional Mg2+. Under the mixotrophic condition, the experimental group achieved a final density of 3.10 g L−1, which was higher than that of the control group (2.98 g L−1). There was also no variation in fatty acid composition between the experimental group and the control group. Under the heterotrophic and mixotrophic conditions, the experimental group produced more than 50% saturated fatty and mono-unsaturated fatty acids, and the degree of unsaturation was <137. This result was relatively lower than that of the control.