Enhancement of lipid production in low-starch mutants Chlamydomonas reinhardtii by adaptive laboratory evolution

Adaptive laboratory evolution (ALE) is an effective method to improve microalgal strains. The growth phenotypes of three strains (cc4324, cc4326 and cc4334) of green microalgae Chlamydomonas reinhardtii were enhanced by ALE. As a result, endpoint strains exhibited higher growth rates. Upon the utilisation of ALE strategy, the biomass concentrations of the endpoint strains of cc4324, cc4326 and cc4334 became 1.17, 1.33 and 1.48 times of those of the starting strains. The total lipid content of the original strains was increased gradually from 32% to 36.67% in the endpoint strain cc4326 and abruptly increased from 24.27% to 44.67% in the endpoint strain cc4334 by nitrogen starvation. Slight growth impairment was also observed in low-starch mutants exposed to nitrogen starvation stress. However, this impairment was quickly resolved after nitrogen was replenished. These findings demonstrated that the biomass concentration and lipid productivity of low-starch mutants can be enhanced by ALE.