Genetic Control of Defective Cell Shape and Osmotic-Sensitivity in a Mutant of Salmonella typhimurium

Abstract

DA82, a complex strain of Salmonella typhimurium characterized by osmotic-sensitivity, spheric cell shape, and increased sensitivity to penicillin and cycloserine, was submitted to genetic analysis. Osmotic-resistant transductants that recover simultaneously normal cell shape and normal sensitivity to antibiotics were selected on low osmolality medium (NoS-A) at 43°. Complete revertants were not found; however, it was possible to isolate partial revertants displaying temporary arrest of cell division in NoS-broth, but no cell death. Those partial revertants retained round cell shape and sensitivity to antibiotics. Conjugation crosses located the mutation responsible for the lack of growth on NoS-A (env-4) in the region 102–108 min. No cotransduction with close markers was observed in tests mediated by phage KB1, yet, joint transduction of env-4 with argE, cod, aroC, and strA was found employing phage P1. The gene order is argE-cod-env-aroC-strA. Thus, env-4 appears to belong to the Salmonella locus homologous to E. coli envB locus. Isogenic strains carrying env + or envB4 allele were prepared by transduction and studied. Mutation envB4 produces abnormal cell shape, increases sensitivity to penicillin, cycloserine, deoxycholate, and UV irradiation; furthermore, it increases cell autolysis and modifies the phenotypic response to several carbohydrates on pH indicator media, envB4 transductants show temporary inhibition of cell division in NoS-broth, but no exponential death. It is suggested that strain DA82 carries at least two envelope mutations: envB4, which is stable and pleiotropic, and an unidentified mutation which, in the presence of the envB4 allele, causes exponential cell inactivation upon osmotic downshock.