Artificial microRNA-mediated knockdown of pyruvate formate lyase (PFL1) provides evidence for an active 3-hydroxybutyrate production pathway in the green alga Chlamydomonas reinhardtii

Artificial microRNA technology was investigated as a means of down regulating metabolic pathways in the green alga Chlamydomonas reinhardtii, targeting pyruvate formate lyase (PFL1), which catalyzes the conversion of pyruvate to acetyl-CoA and formate during anoxic conditions. Two transformants with an 80-90% reduction in target protein and mRNA levels were identified. Nuclear magnetic resonance spectroscopy confirmed a substantial decrease in the production of formate in the knockdown lines during dark anoxic conditions and a re-routing of metabolism leading to enhanced production of ethanol and lactate. Under microaerobic conditions in the light, induced by sulphur-deprivation, knock-down of PFL1 resulted in reduced formate and ethanol production, increased net consumption of acetate and the excretion of lactate but no increase in the production of hydrogen. In addition the production of 3-hydroxybutyrate was identified in knock-down line cultures during the transition between microaerobic and anoxic conditions. Overall our results indicate that microRNA knock-down is a useful tool to manipulate anaerobic metabolism in C. reinhardtii.