Production of xylitol by recombinant microalgae.

Microalgae have received significant attention recently as a potential low-cost host for the production of next-generation biofuels and natural products. Here we show that the chloroplast genome of the eukaryotic green microalga Chlamydomonas reinhardtii can be genetically engineered to produce xylitol through the introduction of a gene encoding a xylose reductase (XR) from the fungi Neurospora crassa. Increased levels of heterologous protein accumulation and xylitol production were achieved by synthesizing the XR gene in the chloroplast codon bias and by driving expression of the codon-optimized XR gene using a 16S/atpA promoter/5'-UTR fusion. These results demonstrate the feasibility of engineering microalgae to produce xylitol, and show the importance of codon optimizing the XR gene and using the 16S/atpA promoter/5'-UTR fusion to express XR in the chloroplast of C. reinhardtii.