Abstract
A mutant strain of Escherichia coli K12 grows well on galactose, lactose, or arabinose, but exhibits poor growth on glucose and a number of other common carbon sources. Defective growth on glucose is partially overcome by prior growth on galactose. Resting cells and growing cultures utilize galactose in preference to glucose when both sugars are present in the medium, although the enzymes for glucose utilization are present in normal amounts. However, the repressive effect of glucose on inducible enzyme formation is lacking. The mutant is characterized by a marked lack of crypticity toward β-galactosides, and lactose is rapidly taken up and hydrolyzed by resting cells. Uptake of galactosides is not inhibited by glucose, contrary to what is observed in the wild type. The defect appears to be in the transport mechanism for glucose. This defect results in a lack of control by glucose of galactose or galactoside uptake.
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