Temperature-sensitive mutants of bacteriophage SH-133 specific for the hydrogen bacterium Pseudomonas facilis:...

Seventeen temperature-sensitive mutants of bacteriophage SH-133 have been isolated following mutagenesis with UV-light, nitrosoguanidine, and ethyl methanesulfonate. The mutants were classified into 15 complementation groups according to their ability to complement each other at 32 degrees C, the nonpermissive temperature. Each mutant was studied with regard to the relationship between its ability to multiply in heterotrophically (H-) and autotrophically (A-) grown Pseudomonas facilis cells. At 27 degrees C, the permissive temperature, the plaque-forming ability of the 17 mutants and wild-type phage was reduced 10-fold in A-grown cells. At 32 degrees C, mutants belonging to 10 groups exhibited identical levels of multiplicity-dependent leak under both modes of growth. However, the infection of A-grown cells by mutants belonging to the remaining five groups resulted in as much as 500-fold inhibition of multiplicity-dependent leak when contrasted with the infection of cells grown heterotrophically. These observations indicate that the expression of five SH-133 phage cistrons is defective when multiplication proceeds under autotrophic metabolism. Seven mutants were found to differ from the wild-type phage with regard to thermal stability at 56 degrees C which suggests that they possess altered structural proteins. Four of the seven thermosensitive mutants exhibited reduced levels of multiplicity-dependent leak in A-grown cells. The data suggest that the reduction in plaque-forming ability of SH-133 in A-grown cells is caused by a defect in the expression of specific phage structural components.