Microalgae possess great potential as a source of sustainable energy, but the intrinsic inefficiency of photosynthesis is a major challenge to realize this potential. Photosynthetic organisms evolved phototaxis to find optimal light condition for photosynthesis. Here we report a microfluidic screening using competitive phototaxis of the model alga, Chlamydomonas reinhardtii, for rapid isolation of strains with improved photosynthetic efficiencies. We demonstrated strong relationship between phototaxis and photosynthetic efficiency by quantitative analysis of phototactic response at the single-cell level using a microfluidic system. Based on this positive relationship, we enriched the strains with improved photosynthetic efficiency by isolating cells showing fast phototactic responses from a mixture of 10,000 mutants, thereby greatly improving selection efficiency over 8 fold. Among 147 strains isolated after screening, 94.6% showed improved photoautotrophic growth over the parental strain. Two mutants showed much improved performances with up to 1.9- and 8.1-fold increases in photoautotrophic cell growth and lipid production, respectively, a substantial improvement over previous approaches. We identified candidate genes that might be responsible for fast phototactic response and improved photosynthesis, which can be useful target for further strain engineering. Our approach provides a powerful screening tool for rapid improvement of microalgal strains to enhance photosynthetic productivity.
Bibliographical noteFunding Information:
This work was mainly supported by the grant (2014M1A8A1049278) from Korea CCS R&D Center of the NRF funded by the Ministry of Science, ICT, & Future Planning of Korea. S.J.S. acknowledges support from the Korea Institute of Energy Technology Evaluation and Planning and Ministry of Trade, Industry & Energy of in “Energy Efficiency & Resources Technology R&D” project Korea (20152010201900), the National Research Foundation of Korea (NRF) grants (grant No. NRF-2013R1A2A1A01015644/2010-0027955) and University-Institute Cooperation Program (2013).
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