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

Highlights • Chloroplastic transgenic C. reinhardtii was developed that stably expressed malate synthase. • This transgenic strain showed a more 19% increase in dry cell weight than wild-type strain. • Transcripts of MDH4 , ACS3 , ICL1 , and MAS1 were increased, and F v /F m was decreased. • Upregulation of heterotrophic metabolism might be involved in biomass increase. • This could serve as a valuable strain for treating wastewater containing acetate and glyoxylate. Abstract 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 F v /F m 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. [ABSTRACT FROM AUTHOR]