Metabolic profiling reveals growth related FAME productivity and quality of Chlorella sorokiniana with different inoculum sizes

Abstract

Inoculum size strongly affects cell growth and lipid accumulation of microalgae, one of the most potential biodiesel feedstock, however, the metabolic mechanism(s) of the lipid biosynthesis upon inoculum size has not been fully explored yet. The effects of inoculum size on cell growth, lipid accumulation, and metabolic changes of a green microalga Chlorella sorokiniana were investigated. In our experimental range of inoculum size, the productivity and the cetane number (CN) of fatty acid methyl esters (FAME) increased with increasing initial cell density, and the inoculum of 1 × 10⁷ cells mL⁻¹ processed much higher productivity (up to 2.02‐fold) and CN (up to 1.19‐fold) of the FAME than the others. A significant correlation between the metabolic profile and quantity and quality of lipid production was revealed by partial least‐squares to latent structures (PLS) analysis, and 15 key metabolites were identified. Most of those metabolites were involved in the photosynthetically fixed carbon metabolism. Furthermore, light intensity as one of the vital limitation factors for the high inoculum size cultivation was evaluated by illumination assay and the results revealed that increasing light intensity could improve the polyunsaturated fatty acids composition and lipid accumulation of C. sorokiniana. The lipid productivity of the culture was improved by 71.21% with the light intensity of 110 µmol m⁻² s⁻¹, compared to that under the irradiance of 65 µmol m⁻² s⁻¹. Biotechnol. Bioeng. 2012; 109:1651–1662. © 2012 Wiley Periodicals, Inc.

To investigate the metabolic relevance between fatty acid methyl esters (FAME) production and inoculum size, Lu and coworkers studied the effects of inoculum size on cell growth, lipid accumulation and the metabolism alternations in Chlorella sorokiniana. The partial least‐squares to latent structures analysis showed a tight correlation existing between the metabolic profile and the FAME production. The subsequent illumination assay confirmed that light intensity might be the vital limiting factor in the high initial cell density culture.