Engineering of Corynebacterium glutamicum for xylitol production from lignocellulosic pentose sugars

• Construction of recombinant Corynebacterium glutamicum for co-conversion of xylose and arabinose to xylitol.
• Validation of recombinants for xylitol production using mineral medium containing combinations of sugars.
• Arabitol free biotransformation of pentose sugar hydrolysate to xylitol.

Xylitol is a non-fermentable sugar alcohol used as sweetener. Corynebacterium glutamicum ATCC13032 was metabolically engineered for xylitol production from the lignocellulosic pentose sugars xylose and arabinose. Direct conversion of xylose to xylitol was achieved through the heterologous expression of NAD(P)H-dependent xylose reductase (xr) gene from Rhodotorula mucilaginosa. Xylitol synthesis from arabinose was attained through polycistronic expression of l-arabinose isomerase (araA), d-psicose 3 epimerase (dpe) and l-xylulose reductase (lxr) genes from Escherichia coli, Agrobacterium tumefaciens and Mycobacterium smegmatis, respectively. Expression of xr and the synthetic araA-dpe-lxr operon under the control of IPTG-inducible Ptac promoter enabled production of xylitol from both xylose and arabinose in the mineral (CGXII) medium with glucose as carbon source. Additional expression of a pentose transporter (araTF) gene enhanced xylitol production by about four-fold compared to the parent strain. The constructed strain Cg-ax3 produced 6.7 ± 0.4 g/L of xylitol in batch fermentations and 31 ± 0.5 g/L of xylitol in fed-batch fermentations with a specific productivity of 0.28 ± 0.05 g/g cdw/h. The strain Cg-ax3 was also validated for xylitol production from pentose rich, acid pre-treated liquor of sorghum stover (SAPL) and the results were comparable in both SAPL (27 ± 0.3 g/L) and mineral medium (31 ± 0.5 g/L).