D-xylose dehydrogenase from coryneform bacteria and process for preparing D-xylonate

A coryneform bacterial cell, wherein the coryneform bacterial cell has an enhanced expression and/or increased activity, compared to the expression of the respective parent gene or enzyme in a wild type coryneform bacterial cell, of a homologous D-xylose dehydrogenase comprising an amino acid sequence that has at least 70% identity to the amino acid sequence according to SEQ ID NO. 2, wherein the coryneform bacterial cell comprises a nucleic acid sequence with one or more nucleotide substitutions or nucleotide deletions in the operatively linked IolR binding sites of the iolT1 gene selected from the group containing nucleic acid sequences according to SEQ ID NO. 9 and SEQ ID NO. 10, which enhances expression and/or increases activity of the homologous D-xylose dehydrogenase in the coryneform bacterial cell.