Ampicillin-Resistant Mutants of Escherichia coli K-12 with Lipopolysaccharide Alterations Affecting Mating Ability and Susceptibility to Sex-Specific Bacteriophages

Abstract

Mutations from moderate (class I) to high (class III) ampicillin resistance in a male and a female strain of Escherichia coli K-12 have been found to be accompanied by surface alterations, first demonstrated as hindrance in the formation of mating pairs. These changes have now been studied with the ribonucleic acid phage MS2, and especially with the “female-specific” phage φW. Several class III mutations in male and female strains were found to make the cells susceptible to phage φW and to reduce their abilities to form mating pairs. Spontaneous phage φW-resistant mutants isolated from class III strains were found also to have acquired changes in ampicillin resistance and ability to form mating pairs. One mutant had reverted to parental class I type in all three properties. Lipopolysaccharides (LPS) prepared from φW-sensitive class III strains inactivated the phage in vitro, whereas LPS from phage-resistant strains had no effect. Carbohydrate analyses of LPS preparations showed that two class III mutants, compared to their parental strains, had lost significant parts of the rhamnose, galactose, and glucose from the LPS. One of the phage φW-resistant mutants showed a partial restoration of its carbohydrate composition. Other φW-resistant mutants showed, instead, further losses of carbohydrates in their LPS. It is suggested that genes exist which simultaneously mediate a female-specific mating site, ampicillin resistance, and the receptors for phage φW.