Myo ‐inositol facilitators IolT1 and IolT2 enhance d ‐mannitol formation from d ‐fructose in Corynebacterium glutamicum

Reduction of d ‐fructose to d ‐mannitol by whole‐cell biotransformation with recombinant resting cells of Corynebacterium glutamicum ATCC13032 requires the coexpression of mdh and fdh , which encode mannitol and formate dehydrogenases, respectively. However, d ‐mannitol formation is limited by the uptake of d ‐fructose in its unphosphorylated form, because additional expression of the sugar facilitator from Zymomonas mobilis resulted in a significantly increased productivity. Here we identified similarities of the myo ‐inositol transporters IolT1 and IolT2 of C. glutamicum to the sugar facilitator of Z. mobilis . The myo ‐inositol transporter genes were both individually overexpressed and deleted in recombinants expressing mdh and fdh . Biotransformation experiments showed that the presence and absence, respectively, of IolT1 and IolT2 significantly influenced d ‐mannitol formation, indicating a d ‐fructose transport capability of these transporters. For further evidence, a C. glutamicum Δ ptsF mutant unable to grow with d ‐fructose was complemented with a heterologous fructokinase gene. This resulted in restoration of growth with d ‐fructose. Using overexpressed iolT1, mdh and fdh , d ‐mannitol formation obtained with C. glutamicum was 34.2 g L −1 , as opposed to 16 g L −1 formed by the strain overexpressing only mdh and fdh , showing the suitability of myo ‐inositol transporters for d ‐fructose uptake to obtain d ‐mannitol formation by whole‐cell biotransformation with C. glutamicum .