The myo-inositol/proton symporter IolT1 contributes to D-xylose uptake in Corynebacterium glutamicum

Corynebacterium glutamicum has been engineered to utilize D-xylose as sole carbon and energy source. Recently, a C. glutamicum strain has been optimized for growth on defined medium containing D-xylose by laboratory evolution, but the mutation(s) attributing to the improved-growth phenotype could not be reliably identified. This study shows that loss of the transcriptional repressor IolR is responsible for the increased growth performance on defined D-xylose medium in one of the isolated mutants. Underlying reason is derepression of the gene for the glucose/myo-inositol permease IolT1 in the absence of IolR, which could be shown to also contribute to D-xylose uptake in C. glutamicum. IolR-regulation of iolT1 could be successfully repealed by rational engineering of an IolR-binding site in the iolT1-promoter. This minimally engineered C. glutamicum strain bearing only two nucleotide substitutions mimics the IolR loss-of-function phenotype and allows for a high growth rate on D-xylose-containing media (mu(max) = 0.24 +/- 0.01 h(-1)).