Mutations habilitant Escherichia colià croître sur acides gras moyens

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Abstract
New spontaneous mutants of Escherichia coli able to use butyrate or valerate as carbon source have been studied for their growth, adaptation lag and the level of enzymes which may participate in the utilisation of these compounds.Each mutant acquires the simultaneous constitutivity for uptake of these fatty acids, CoA transferase and high thiolase activities. This mutation designated as butR does not affect the regulation of the β‐oxidation nor that of the glyoxylate cycle.Induction or mutation for constitutivity (oleR) of β‐oxidation act multiplicatively on the level of thiolase derepressed by the butR mutation.If the presence of CoA transferase, thiolase and C4–C5 fatty acids entry system is a prerequisite of the growth ability on these fatty acids, the genetic constitutivities (and not the preinduction) of the β‐oxidation (oleR) and particularly of the glyoxylic cycle (aceD) greatly increase the growth capacity. This implies that not only the C, and C, fatty acyl derivatives are very poor inducers of β‐oxidation, as already reported by others, but that some products of their catabolism repress the glyoxylic cycle.The acquisition of the new growth capacity is thus accomplished by spontaneous mutations affecting regulatory processes; one of these discloses activities which are cryptic in the normal parental strains; the physiological significance of these enzymatic potentialities in wild strains and the mechanism of the interaction between two different regulatory units brought to light here are some of the open issues.

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