THERMOSENSITIVE CELL-GROWTH MUTANTS OF ENTEROCOCCUS-HIRAE THAT ELONGATE AT NONPERMISSIVE TEMPERATURE ARE STIMULATED TO DIVIDE BY PARENTAL AUTOLYTIC ENZYMES

A series of thermosensitive cell growth mutants of Enterococcus hirae have been isolated. Most of these mutants elongate and some show reduced autolytic activity when incubated at the non-permissive temperature (42 degrees C) in comparison to the wild-type incubated at the same temperature. When mutants were incubated for longer than 15 min at 42 degrees C and were then shifted to 30 degrees C, a lag proportional to the time of preincubation at 42 degrees C was observed before division, indicating that a certain time is necessary to restore normal levels of an active molecule(s) needed for septum formation and division. The addition of wild-type muramidase-1 permitted the immediate formation of septa and a single cell division; further addition of the enzyme stimulated the cells to divide once again. The other E. hirae autolytic enzyme, peptidoglycan-hydrolase-2, which is found in the culture medium, seemed to be involved in separation of daughter cells but may also take over the function of muramidase-1. A key role of both enzymes in septum formation and division is postulated.