SUMMARY: Batch cultures of X mut 1 lacking methanol dehydrogenase activity were grown in media containing both methylamine and ethanol as carbon source. The pattern of growth did not show the characteristics of diauxic growth but methylamine was the preferred substrate. When the concentration of the methylamine in the medium fell to 9 mM (0.8 mM), ethanol was utilized and the two substrates were then utilized simultaneously until the methylamine was exhausted from the medium. Growth then continued using ethanol. The levels of key enzymes and the values for the two substrates supported this growth pattern and accounted for the measured uptake of the two substrates from the medium. When the wild-type X was used in similar experiments, methylamine and ethanol appeared to be used simultaneously. However, the values for methanol and ethanol were the same until ethanol dehydrogenase activity was induced. This suggested that the ethanol utilization observed before the induction of ethanol dehydrogenase was due to the activity of methanol dehydrogenase induced by the presence of methylamine. When this was taken into account the growth pattern obtained with the wild-type organism was the same as that seen with the mutant.


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