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Many yeasts and fungi can assimilate L-arabinose via a complex pathway consisting of two reduction, two oxidation and phosphorylation.
Unspecific aldose reductase catalyzes the reduction of L-arabinose to L-arabitol, and L-arabitol dehydrogenase (LAD) oxidizes L-arabitol to L-xylulose. This is subsequently reduced to xylitol by L-xylulose reductase (LXR). After that, xylitol dehydrogenase (XDH) catalyzes the oxidation of xylitol to D-xylulose. D-xylulose is converted to D-xylulose 5-phosphate by xylulose kinase (XK) and then enters the pentose phosphate pathway (PPP). However, Candida tropicalis ATCC 20336 cannot grow on media containing L-arabinose as the sole carbon, which indicates that there is not L-arabinose metabolic pathway in this strain. For consumption of L-arabinose via PPP, bacterial L-arabinose metabolic pathway was introduced to C. tropicalis. Bacillus licheniformis L-arabinose isomerase (araA, AI), E. coli L-ribulokinase (araB, RK) and L-ribulose-5-phosphate 4-epimerase (araD, RPE) were selected and backtranslated using the preferred codons in C. tropicalis.
Codon-optimized genes were synthesized and expressed in C. tropicalis.
The resulting recombinant yeast expressed araBAD successfully and survived utilizing L-arabinose as a sole carbon source.