Isolation and characterization of immunity temperature sensitive mutants of Enterobacter cloacae harbouring the cloacinogenic factor DF13

Summary Enterobacter cloacae cells, harbouring the cloacinogenic factor DF13 (Clo DF13) are immune to the cloacin they produce. We describe the isolation of eleven Enterobacter cloacae (Clo DF13) mutants, which are immune at 30°C, but lose their immunity at 42°C. The temperature sensitive immunity (Imm^ts) of these mutants appeared not to be transferable together with the Clo DF13 factor to non-cloacinogenic acceptor strains. Apparently host mutations are involved in the Imm^ts phenotype. Two different groups of Imm^ts mutants could be identified. Imm^tsC6 and Imm^tsC8, representatives of each group, have been compared with the parent strain. Imm^tsC6 as well as Imm^tsC8 is sensitive to crude cloacin at 42°C. Imm^ts mutants appeared to be also sensitive to cell components other than cloacin, indicating that the Imm^ts mutations may result in pleiotropic changes of cell properties.The Imm^tsC6 mutant is sensitive to deoxycholate and osmotic shock at 42°C. Spheroplasts of Imm^tsC6 cells incubated at 42°C are sensitive to DOC at 42°C and 30°C. The pleiotrophic changes of the Imm^tsC6 mutant may be attributed to a defect in the cell membrane.The Imm^tsC8, incubated at 42°C, is sensitive to deoxycholate, osmotic shock, ethylene-diaminetetraacetic acid, dyes, drugs and UV. Furthermore they form filaments. Imm^tsC8 spheroplasts are as sensitive to deoxycholate as the parent strain at 42°C. The pleiotropic changes in the phenotype of Imm^tsC8 are considered to be the result of a defect in the outer layers of the cell envelope, most likely the lipopolysaccharide layer.The possible relationship between the observed structural defects in the cell envelope of Imm^ts mutants and the phenomenon of immunity have been discussed.