UC San Diego

Human need for food and fuel has disturbed the balance of the biosphere thus triggering a catastrophe known as the Anthropocene Extinction. The use of microalgae in the biotechnology field offers multiple solutions that could alleviate the demand human activity imposes on the ecosystem. The most well studied microalga is the model organism Chlamydomonas reinhardtii, resulting in multiple genetic tools available in the alga for recombinant protein expression. However, the yields of recombinant protein expression are not high enough to be commercially viable, therefore this organism is usually not considered as a biotechnological host.To boost the recombinant protein productivity in Chlamydomonas reinhardtii two milestones need to be achieved: increased recombinant protein expression at single cell level, and increased number of cells per unit of culture volume. To accomplish higher transgene expression in C. reinhardtii the GAL4/UAS system was adapted into algal protein expression vectors. This system showed a 10-fold improvement in recombinant mRNA and protein accumulation of a reporter gene under the control of a chimeric promoter 5XUAS-AR1. To accomplish higher number of cells, or biomass, per unit of culture volume an optimized algal fed batch bioreactor was designed. Through media optimization we achieved a 1.67-fold improvement in biomass accumulation which in turn yielded a 3-fold improvement over the highest recombinant protein concentration reported in the literature using C. reinhardtii. Finally, an extremophile green alga from the Chlamydomonas genus was isolated from the wild and used to express recombinant GFP. Said extremophile showed robust growth in open ponds thriving in media at pH 11 while continuing to express recombinant protein for the duration of the experiment. These findings highlight the potential of Chlamydomonas reinhardtii to become a robust biotechnological host at commercial scale.