Spontaneous and mutator-induced reversions of an Escherichia coli auxotroph. II. Acetylornithinase activity associated with the different revertant types.

Bacon, Donald F. (Yale University, New Haven, Conn.), and Henry P. Treffers. Spontaneous and mutator-induced reversions of an Escherichia coli auxotroph. II. Acetylornithinase activity associated with the different revertant types. J. Bacteriol. 82:48-53. 1961.-In a preceding communication it was shown that three principal groups of spontaneous revertants from an ornithine-requiring strain of Escherichia coli could be distinguished on the basis of their growth characteristics. They were designated as fast (F) (identical with the wild type), slow-48 (S(48)), and slow-72 (S(72)). The present paper presents data on the acetylornithinase activities as well as precursor accumulations of typical revertants from each group. The enzymatic activity associated with extracts of F revertants did not differ significantly from those of the wild type; the mean activity of extracts from the wild-type and F revertants was 23 units per mg of protein; the mean activity of S(48) revertant extracts was 0.4 units per mg of protein and, similarly, that of the S(72) revertant extracts was 0.06 units per mg of protein. These are, respectively, 1/50 and 1/350 of the wild-type activity. It was estimated that an S(48) culture in minimal broth accumulated 16 mug of N(alpha)-acetylornithine per ml and that an S(72) culture accumulated 60 mug per ml of this compound. Accumulation of this precursor in an F revertant culture was not detected by the assay procedure employed. In an earlier communication we reported that both the S(48) and S(72) revertant types exhibited increasing rates of growth when the growth in minimal broth was followed photometrically Supplements of N(alpha)-acetylornithine and of a sterile supernatant from an S(48) revertant culture which were incorporated into minimal broth failed to modify the unusual curvilinear nature of the growth curve. The data on the enzymatic activities and precursor accumulations support the original classification of revertant groups on the basis of growth rates. The total information at hand is consistent with the notion that reversion from an auxotrophic requirement may result in at least three distinct revertant types, each characterized by a unique growth rate, enzymatic activity, and precursor accumulation.