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J Bacteriol. 1969 November; 100(2): 948-955
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Basis for the Mutational Acquisition of the Ability of Aerobacter aerogenes to Grow on L-Mannose

Department of Biochemistry, Michigan State University, East Lansing, Michigan 48823

ABSTRACT

Growth of Aerobacter aerogenes PRL-R3 on the unnatural hexose L-mannose as a sole carbon source is dependent upon the selection of a mutant. Growth of the mutant on L-mannose did not require the synthesis of novel enzymes for the degradation of L-mannose, since enzymes of the L-rhamnose degradative pathway could serve this function. However, unlike most other apparent gain mutations that have been described, the mutant was not constitutive for the degradative enzymes; isomerase, kinase, and aldolase activities functional in the degradation of both L-mannose and L-rhamnose were induced by either of these hexoses in the wild type as well as in the mutant. The fact that the wild type could metabolize L-mannose also ruled out the possibility that the cells were not permeable to L-mannose. Growth of the wild type on nutrient broth was severely inhibited by L-mannose coincident with the onset of L-mannose metabolism. A similar inhibition of growth of the mutant was overcome in about 2 hr. Both strains utilized L-rhamnose and L-mannose sequentially in a mineral medium containing both of these hexoses; at the onset of L-mannose metabolism, growth of the wild type, but not of the mutant, was inhibited. Thus, wild-type A. aerogenes cannot grow on L-mannose because of the toxicity of L-mannose or its metabolites. A mutation which overcomes the toxicity enables the organism to utilize L-mannose as a sole source of carbon and energy for growth.