Experimental evolution of a novel pathway for glycerol dissimilation inEscherichia coli

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Abstract
Wild-typeEscherichia coli utilizes glycerol aerobically through an inducible pathway mediated by an ATP-dependent kinase and a glycerol 3-phosphate dehydrogenase which is a flavoprotein. A mutant, strain ECL424, employing a novel pathway for glycerol utilization was isolated. The novel pathway is mediated by an NAD-linked dehydrogenase and a dihydroxyacetone specific enzyme II of the phosphoenolpyruvate phosphotransferase system. This study describes the selection from strain ECL424, a derivative which grows more rapidly on glycerol. The derivative, strain ECL428, produces twice the parental levels of both the dehydrogenase and the enzyme II during growth on glycerol. The function of the dehydrogenase in wild-type cells is unknown, although hydroxyacetone (acetol), 3-hydroxy-2-butanone (acetoin), and 1-amino-2-propanone are gratuitous inducers. The induction can be prevented by glucose whose effect can be cancelled by external cyclic AMP. The effects of hydroxyacetone, glucose, and cyclic AMP are attenuated in the two mutants in which the dehydrogenase is produced at high basal levels. The dihydroxyacetone specific enzyme II is inducible by the substrate in both wild-type and mutant strains and serves for growth on the triose.