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Overproduction of recombinant E. coli malate synthase enhances Chlamydomonas reinhardtii biomass by upregulating heterotrophic metabolism

Paik, Sang-Min, Kim, Joonwon, Jin, EonSeon, Jeon, Noo Li
Bioresource technology 2019 v.272 pp. 594-598
Chlamydomonas reinhardtii, acetate-CoA ligase, biomass, chloroplasts, energy, gene overexpression, genetically modified organisms, glyoxylate cycle, isocitrate lyase, malate dehydrogenase, malate synthase, malates, messenger RNA, microalgae, photosynthesis, tricarboxylic acid cycle
High uptake of malate and efficient distribution of intracellular malate to organelles contributed to biomass increase, reducing maintenance energy. In this study, transgenic Chlamydomonas reinhardtii was developed that stably expresses malate synthase in the chloroplast. The strains under glyoxylate treatment showed 19% more increase in microalgal biomass than wild-type. By RNA analysis, transcript levels of malate dehydrogenase (MDH4) and acetyl-CoA synthetase (ACS3), isocitrate lyase (ICL1) and malate synthase (MAS1), were significantly more expressed (17%, 42%, 24%, and 18% respectively), which was consistent with reported heterotrophic metabolism flux analysis with the objective function maximizing biomass. Photosynthetic Fv/Fm was slightly reduced. A more meticulous analysis is necessary, but, in the transgenic microalgae with malate synthase overexpression, the metabolism is likely to more rely on heterotrophic energy production via TCA cycle and glyoxylate shunt than on photosynthesis, resulting in the increase in microalgal biomass.