Temperature-sensitive mutants of Escherichia coli B which can grow in high-osmotic medium at the nonpermissive temperature.

Two temperature sensitive (TS) mutants (C4 tos and D2 tos) were isolated after mutagenesis of E. coli B/SM by N-methyl-N'-nitro-N-nitrosoguanidine (NMNG), which can grow even at 42 C in high-osmotic medium supplemented by addition of sucrose, NaCl or other compounds. Neither of the mutants lyzed when transferred to low-osmotic medium after growning at the nonpermissive temperature in high osmotic medium. One of these mutants, C4 tos, grew at 42 C in a long filamentous form. When bacteria growing exponentially at 30 C were shifted to 42 C, they continued to grow at a reduced rate even in low-osmotic medium. This strain could also grow or start to grow in low-osmotic medium when supplied with a factor or factors secreted from growing bacteria of another strain. This mutant strain could grow in low-osmotic medium at 42 C when it was cultured anaerobically. The other mutant strain obtained (D2 tos) displayed normal morphology even when grown at 42 C. When it was shifted from 30 to 42 C in low-osmotic medium, increase of mass, measured as optical density, continued for a while, but viability, measured as the number of colony-formers, stopped increasing and then decreased rapidly.