It was investigated whether Escherichia coli cultured in a glucose-limited chemostat is able to grow with a series of sugars whose utilization is normally repressed during batch growth with glucose. Cells growing at dilution rates of 02,03 and 0 6 h-' were able to immediately utilize and grow with fructose, mannose, maltose and ribose. Galactose was transported instantaneously but growth started only after a considerable lag. Arabinose was the only sugar tested which was neither transported nor

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... utilized immediately. The results give experimental evidence that in vivo catabolite repression by glucose is absent at the very low glucose concentrations present in chemostat culture. Additionally, the results demonstrate that chemostat-grown cells of E. coli are able to substitute glucose as a carbon and energy source by several other sugars with no lag period.