The lactose system inKlebsiella aerogenesV9A: 6. Lactose transport

Abstract

SUMMARYKlebsiella aerogenesV9A carrying alacplasmid in addition to its chromosomal operon showed strongly positive fermentation of lactose on MacConkey lactose agar plates, and was found to transport the lactose analogue thiomethyl-β-galactoside (TMG) at a rapid rate. The strain that had been freed of the plasmid showed moderate transport due to the chromosomallacoperon. When a plasmid bearing a mutation inlac Ywas inserted into a strain with a normalYgene, the resulting diploid became lactose-negative in phenotype. The presence ofE. coliF′lacfactors that carriedlac Ymutations, whether deletions or missense or nonsense mutations, also renderedlac Y+Klebsiellalactose-negative. Such diploids, after growth in 1% lactose, transported TMG at a much lower rate than the corresponding plasmid-freelac Y+Klebsiella. However, this interference bylac Y−plasmids with the expression of the chromosomallac Ygene was not seen when cells were induced with IPTG or when the chromosomal and plasmidlacoperons were both constitutive. It was found that this effect of the plasmids was dependent on their possessing an intactlacZgene.