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

Abstract

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 (Immts) 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 Immts phenotype. Two different groups of Immts mutants could be identified. ImmtsC6 and ImmtsC8, representatives of each group, have been compared with the parent strain. ImmtsC6 as well as ImmtsC8 is sensitive to crude cloacin at 42°C. Immts mutants appeared to be also sensitive to cell components other than cloacin, indicating that the Immts mutations may result in pleiotropic changes of cell properties. The ImmtsC6 mutant is sensitive to deoxycholate and osmotic shock at 42°C. Spheroplasts of ImmtsC6 cells incubated at 42°C are sensitive to DOC at 42°C and 30°C. The pleiotrophic changes of the ImmtsC6 mutant may be attributed to a defect in the cell membrane. The ImmtsC8, incubated at 42°C, is sensitive to deoxycholate, osmotic shock, ethylene-diaminetetraacetic acid, dyes, drugs and UV. Furthermore they form filaments. ImmtsC8 spheroplasts are as sensitive to deoxycholate as the parent strain at 42°C. The pleiotropic changes in the phenotype of ImmtsC8 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 Immts mutants and the phenomenon of immunity have been discussed.