Defective transport and other phenotypes of a periplasmic "leaky" mutant of Escherichia coli K-12

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Abstract
A mutant of E. coli K-12 deficient in high-affinity leucine transport and related binding proteins was obtained by selecting for azaleucine resistance after bacteriophage Mu mutagenesis. The cause was a generalized loss of periplasmic binding proteins and a sharp decrease in the activity of transport systems requiring them. Other transport systems, resistant to osmotic shock and present in membrane vesicles, were affected to a lesser degree or not at all. The mutation, designated lky::Mucts, was a pleiotropic envelope mutation, rendering the mutant sensitive to ionic and non-ionic detergents, antibiotics and EDTA, the strain acquired tolerance to colicins E1, E2 and E3 while remaining normally sensitive to a variety of bacteriophages. An analysis of the lipopolysaccharide [LPS] of parent and mutant strains revealed a 2-fold reduction in the neutral sugar content of the core oligosaccharide of the lky strain but no change in sensitivities to phages which utilize LPS or outer membrane proteins for absorption. The lky::Mucts locus was mapped by transduction and located near or in the tolPAB gene cluster linked to gal. Secondary mutations suppressing the detergent sensitivity of lky arose at a frequency of 10-7, yielding a variety of new phenotypes. The lky::Mucts mutation did not give rise to obvious alterations in the gross morphology of the cell or in cell division.