Effect of heat treatment on phage susceptibility of a Mycobacterium smegmatis strain.

Plating efficiency of mycobacteriophage butyricum (By) proved to be 10(-4)-10(-3) on Mycobacterium smegmatis strain Rabinowitz (M. sm. R.) cells being in the logarithmic phase. This increased to 10(-2)-10(-1) when the cells were held at 50-57 degrees C for 2 h before infection. After replacing the cells to 37 degrees C, plating efficiency of the phages returned to the starting values. This phenomenon could be inhibited by nalidixic acid (150 micrograms/ml) and chloramphenicol (10 micrograms/ml) but not by mitomycin C (0.05 microgram/ml). No return to the starting plating efficiency values were observed, if incubation of cells at 37 degrees C after heat treatment has been performed in buffer. The data suggest that By phage propagation in M. sm. R. cells is inhibited by a thermosensitive protein.