Metabolic engineering of Cyanidioschyzon merolae

Abstract

Algae are expected to be promising alternative sources of biofuels, foods, and cosmetics. The unicellular red alga Cyanidioschyzon merolae is potentially useful for producing high concentrations of desirable biomaterials by metabolic engineering. C. merolae is genetically traceable and can thrive at low pH (1-5) and high temperatures (25-50°C), which are harmful to many other organisms. Thus, this alga can be suitable for outdoor cultivation without the risk for contamination from other undesirable organisms. Recent studies regarding C. merolae have reported enhanced triacylglycerol (TAG) production, which can be used for biodiesel production, by genetic modification. Introducing cyanobacterial acyl-acyl carrier protein (ACP) reductase in C. merolae led to temporary TAG accumulation via an artificial metabolic pathway. The omics analyses showed that acyl-ACP reductase expression resulted in upregulating endogenous aldehyde dehydrogenase and the endogenous fatty acid synthetic pathway in chloroplasts. Another study expressed the 12-kDa FK506-binding protein of Saccharomyces cerevisiae in C. merolae and succeeded in increasing TAG levels by adding rapamycin. The omics analyses suggested that the target of rapamycin (TOR) regulated the expression of TAG-synthesizing enzymes, glycerol- 3-phosphate acyltransferase, and acyl-CoA:diacylglycerol acyltransferase. Therefore, the combination of metabolic engineering and the evaluation of the effects in C. merolae by omics analyses will help in understanding the regulatory mechanism of metabolism. In addition, recent studies have started to find culture conditions that increase TAG accumulation while maintaining the cellular growth. Combinations of these cultivation techniques and genetic manipulations will leads to production of desirable biomolecules on a large scale in the future.