Improving the optimum yield and growth of <i>Chlamydomonas reinhardtii</i> CC125 and CW15 using various carbon sources and growth regimes

Abstract

Chlamydomonas reinhardtii CC125 (wild type) and CW15 (cell wall mutants) were feed up on solid and liquid Tris phosphate (TP) media with various concentrations of acetate, glycerol(10-100 mM) or methanol (0.01-718 mM) and cultivated under phototrophic, mixotrophic and heterotrophic conditions. Use of 10 and 35 mM acetate and 10 and 50 mM glycerol under constant 38 μE m⁻² s⁻¹ light illumination (mixotrophically) was the optimum condition for both strains to have a higher biomass and growth compared to other carbon sources and concentrations. Both strains had a quicker growth rate in just 35 mM of acetate and 10 mM glycerol although feed of algal cells on 35 mM acetate produced more and quicker biomass. In use of 10 mM acetate in micro plate and tissue culture flasks, CW15 had a maximum growth rate of 5.3×10⁴ and 1.3×10⁴ cells/hour; while on use of 35 mM acetate, the growth rate was 8.8×10⁴ (micro plate) and 4.0×10⁴ cells/hour (tissue culture flasks). Wild type had a maximum 2.7×10⁴ (micro plate) and 4×10³ (tissue culture) cells/hour in use of 10 mM acetate. In feed of CC125 with 35 mM acetate, growth rate correspondingly for micro plate and tissue culture flasks was 2.5×10⁴ and 2.6×10⁴ cells/ hour. Among the two strains, CW15 with specific growth rate of 8.8×10⁴ cells/hour (in micro plates) and 4.0×10⁴ cells/hour (in tissue culture flasks) on 35 mM acetate also grew quicker than CC125. Susceptibility to bacterial contamination was checked on both strains and we also found that, just as the absence of a cell wall in CW15 accelerated the growth, it also appeared to increase the chance of contamination by about twofold compared to the wild type but this can be minimized by the use of antibiotics in the growth media.

Keywords: Heterotrophic growth, mixotrophic growth, acetate, glycerol methanol Chlamydomonas, CC125, CW15