UTILIZATION OF D-RIBOSE THROUGH D-XYLOSE TRANSPORTER

An Escherichia coli mutant defective in high-affinity D-ribose transpo rt is able to utilize the sugar as a sole carbon source, suggesting th at other transport systems for D-ribose exist. In order to search for such transporters, transposon mutagenesis was carried out in an rbsB-n egative strain containing ribokinase (rbsK) for sugar phosphorylation. Insertions showing an enhanced ribose growth were isolated and mapped in xylA and its promoter region. The mutations increased not only the ribose uptake but also the expression of xylFGH encoding an ABC (ATP- binding cassette)-type transporter for D-xylose. Secondary mutations a bolishing the ribose-utilizing phenotype were obtained both in the xyl FG genes coding for the xylose high-affinity transporter and in xylR t hat is required for the xyl gene expression. Ribose uptake was also re duced by the secondary mutations. An overexpression of sylFGH under Pt -rc promoter supported enhanced growth on ribose. These results indica te that D-ribose can be transported through the XylFGH transporter. (C ) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.