Conversion of l-arabinose to l-ribose by genetically engineered Candida tropicalis

Abstract

l -Ribose, a starting material for the synthesis of l -nucleoside, has attracted lots of attention since l -nucleoside is responsible for the antiviral activities of the racemic mixtures of nucleoside enantiomers. In this study, the l -ribulose-producing Candida tropicalis strain was engineered for the conversion of l -arabinose to l -ribose. For the construction of a uracil auxotroph, the URA3 gene was excised by homologous recombination. The expression cassette of codon-optimized l -ribose isomerase gene from Acinetobacter calcoaceticus DL-28 under the control of the GAPDH promoter was integrated to the uracil auxotroph. The resulting strain, K1 CoSTP2 LsaAraA AcLRI, was cultivated with the glucose/ l -arabinose mixture. At 45.5 h of fermentation, 6.0 g/L of l -ribose and 3.2 g/L of l -ribulose were produced from 30 g/L of l -arabinose. The proportion between l -ribose and l -ribulose was approximately 2:1 and the conversion yield of l -arabinose to l -ribose was about 20% ( w / w ). The l -ribose-producing yeast strain was successfully constructed for the first time and could convert l -arabinose to l -ribose in one-pot fermentation using the mixture of glucose and l -arabinose. Supplementary Information The online version contains supplementary material available at 10.1007/s00449-020-02506-2.

Current advances in Candida tropicalis: Yeast overview and biotechnological applications

“…l ‐Ribose and l ‐ribulose are molecules that have gained prominence recently, as they can be used to produce l ‐nucleosides, which are starting materials to make promising antivirals drugs based on l ‐nucleoside analogues, such as lamivudine, clevudine, and telbivudine. These antivirals act by stopping viral DNA/RNA synthesis and, consequently, viral replication 103–105 . In comparison with their d ‐counterparts, antiviral drugs based on l ‐nucleosides have shown higher antiviral activities/metabolic stabilities and lower toxicities.…”

“…The genetically engineered strain produced 9 g/L of l‐ ribulose with a yield of 30% (w/w). For l‐ ribose production, the l‐ ribose isomerase gene from Acinetobacter calcoaceticus was expressed in the engineered strain cited above, and a production of 6.0 g/L of l‐ ribose with a yield of 20% (w/w) was achieved 104 …”

“…These antivirals act by stopping viral DNA/RNA synthesis and, consequently, viral replication. [103][104][105] In comparison with their d-counterparts, antiviral drugs based on l-nucleosides have shown higher antiviral activities/metabolic stabilities and lower toxicities. l-Ribulose is first enzymatically converted to l-ribose, which is converted to l-nucleosides.…”

“…For l-ribose production, the lribose isomerase gene from Acinetobacter calcoaceticus was expressed in the engineered strain cited above, and a production of 6.0 g/L of l-ribose with a yield of 20% (w/w) was achieved. 104 RNA is a macromolecule involved in several cellular processes, being of extreme importance to the cell and to the development of organisms. Besides its importance to the cell, RNA production is also targeted for industrial purposes as it can be degraded into 5′-nucleotides, which can be used as flavors and flavor enhancers in the food industry.…”