Characterization of sugar mixtures utilization by an Escherichia coli mutant devoid of the phosphotransferase system

Due to catabolite repression in microorganisms. sugar mixtures cannot be me tabolized in a rapid and efficient manner. Therefore, the development of mu tant strains that avoid this regulatory system is of special interest to fe rmentation processes. In the present study, the utilization of sugar mixtur es by an Escherichia coli mutant strain devoid of the phosphotransferase sy stem (PTS) was characterized. This mutant can transport glucose (PTS- Gluco se(+) phenotype) by a non-PTS mechanism as rapidly as its wild-type parenta l strain. In cultures grown in minimal medium supplemented with glucose-xyl ose or glucose-arabinose mixtures, glucose repressed arabinose- or xylose-u tilization in the wild-type strain. However, under the same culture conditi ons with the PTS- Glucose(+) mutant, glucose and arabinose were co-metaboli zed. but glucose still exerted a partial repressive effect on xylose consum ption. In cultures growing with a triple mixture of glucose-arabinose-xylos e, the wild-type strain sequentially utilized glucose. arabinose and finall y, xylose. In contrast, the PTS- Glucose(+) strain co-metabolized glucose a nd arabinose, whereas xylose was utilized after glucose-arabinose depletion . As a result of glucose-arabinose co-metabolism, the PTS- Glucose(+) strai n consumed the total amount of sugars contained in the culture medium 16% f aster than the wildtype strain. [C-14]-Xylose uptake experiments showed tha t in the PTS- Glucose(+) strain, galactose permease increases xylose transp ort capacity and the observed partial repression of xylose utilization depe nds on the presence of intracellular glucose.