Rapid Lipid Induction in Chlorella sp. by UV-C Radiation

Abstract

Rapid induction of lipid accumulation in microalgae is an important prerequisite towards the use of microalgae as a feedstock for biodiesel production. In this study, we present a novel approach to induce lipids in Chlorella sp. within 24 h by short-term UV-C radiation (UVR) stress at different energy intensities ranging from 0 to 1000 mJ/cm2. Increase in the lipid fluorescence was measured by Nile red staining and fluorescence-activated cell sorting analysis followed by gas chromatography-mass spectrometry. Lipid fluorescence was significantly increased in cultures radiated at or above 250 mJ/cm2 compared to the mock-treated control cultures. Lower dosages at 100 and 250 mJ/cm2 led to a near doubling of total fatty acids, with a significant increase in unsaturated fatty acids and also most saturated fatty acids. This study provides a protocol for rapid lipid induction of microalgal cells by UV-C and the possible impact of UV-C radiation on fatty acid metabolism.

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Acknowledgments

We wish to thank the Australian Research Council for financial support.

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Correspondence to Peer M. Schenk.

Electronic Supplementary Material

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Online Resource Figure 1

Analysis of the non-polar fraction of TAGs in Chlorella sp. BR2 treated with different UV-C radiation doses (0–1000 mJ/cm2). (PDF 213 kb)

Online Resource Figure 2

FACS analysis of Chlorella sp. BR2. Shown are cells without Nile red staining (Unstained Cells) and Nile red-stained with different UV-C dosages ranging from 0 mJ/cm2 (Control) to 1000 mJ/cm2 showing P1 and P2 populations. The Y-axis shows fluorescence intensity at the phycoerythrin excitation wavelength of 575 nm, and the X-axis shows the forward scatter based on cell size. (PDF 161 kb)

Online Resource Figure 3

Comparison of different saturated fatty acids present in Chlorella sp. BR2 cultures treated with different doses of UV-C radiation. Values are mean ± SE from three separately grown cultures (n = 3); bars with different letters indicate significant differences (P < 0.05). (PDF 136 kb)

Online Resource Figure 4

Comparison of different unsaturated fatty acids present in Chlorella sp. BR2 cultures treated with different doses of UV-C radiation. Values are mean ± SE from three separately grown cultures (n = 3); bars with different letters indicate significant differences (P < 0.05). (PDF 143 kb)

Online Resource Figure 5

Growth curve of Chlorella sp. BR2 cells. UV-C treatment was applied during the late exponential growth phase (1.6 × 107 cells/mL). Values are mean ± SE from three separately grown cultures (n = 3). (PDF 53 kb)

Online Resource Figure 6

Comparison of total fatty acids present in Chlorella sp. BR2 cells treated with different doses of UV-C radiation. Shown are mean amounts ± SE of total fatty acids in micrograms/cell from three separately grown cultures (n = 3); bars with different letters indicate significant differences (P < 0.05). (PDF 52 kb)

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Sharma, K.K., Li, Y. & Schenk, P.M. Rapid Lipid Induction in Chlorella sp. by UV-C Radiation. Bioenerg. Res. 8, 1824–1830 (2015). https://doi.org/10.1007/s12155-015-9633-y

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Keywords

  • Chlorella
  • Lipids
  • Microalgae
  • PUFA
  • UV-C