4.3 Article

Effects of Methanol on Cell Growth and Lipid Production from Mixotrophic Cultivation of Chlorella sp.

Journal

BIOTECHNOLOGY AND BIOPROCESS ENGINEERING
Volume 16, Issue 5, Pages 946-955

Publisher

KOREAN SOC BIOTECHNOLOGY & BIOENGINEERING
DOI: 10.1007/s12257-010-0394-3

Keywords

methanol; CO2; light and dark cycle; outdoor cultivation; Chlorella sp.

Funding

  1. Korea Institute of Energy Technology Evaluation and Planning (KETEP) [2008-N-BL-HM-E-06]
  2. Korea Govenment Ministry of Knowledge Economy
  3. National Research Foundation of Korea [과C6B2301] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)

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The marine microalga Chlorella sp. was cultivated under mixotrophic conditions using methanol as an organic carbon source, which may also act to maintain the sterility of the medium for long-term outdoor cultivation. The optimal methanol concentration was determined to be 1% (v/v) for both cell growth and lipid production when supplying 5% CO2 with 450 mu E/m(2)/sec of continuous illumination. Under these conditions, the maximal cell biomass and total lipid production were 4.2 g dry wt/L and 17.5% (w/w), respectively, compared to 2.2 g dry wt/L and 12.5% (w/w) from autotrophic growth. Cell growth was inhibited at methanol concentrations above 1% (v/v) due to increased toxicity, whereas 1% methanol alone sustained 1.0 g dry wt/L and 4.8% total lipid production. We found that methanol was preferentially consumed during the initial period of cultivation, and carbon dioxide was consumed when the methanol was depleted. A 12:12 h (light:dark) cyclic illumination period produced favorable cell growth (3.6 g dry wt/L). Higher lipid production was observed with cyclic illumination than with continuous illumination (18.6% (w/w) vs 17.5% (w/w)), and better lipid production was also obtained under mixotrophic rather than autotrophic conditions. Interestingly, under mixotrophic conditions with 12:12 (h) cyclic illumination, high proportions of C-16:0, C-18:0, and C-18:1 were observed, which are beneficial for biodiesel production. These results strongly indicate that the carbon source is important for controlling both lipid composition and cell growth under mixotrophic conditions, and they suggest that methanol could be utilized to scale up production to an open pond type system for outdoor cultivation where light illumination changes periodically.

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