phi 6-resistant phage-producing mutants of Pseudomonas phaseolicola

phi 6R mutants of Pseudomonas phaseolicola HB10Y were isolated and 12 out of 129 spontaneous mutants were found to produce phages during cellular growth. Following mitomycin C treatment 39 out of 82 isolated resistant mutants were phage-producing ones. The decrease in growth rate of these mutants corresponded roughly to the number of phages liberated into the medium. Prolonged storage of the mutants resulted in loss of production which could be regained by growing them with a high multiplicity of phages. The phage production phenomenon was independent of phage adsorption since both adsorbing and non-adsorbing phage-producing mutants were found. Occasionally, the phage-producing strains showed abnormally high numbers of intracellular phage particles in sectional material. The producers were found to be 2 to 5 times more resistant than the normal host or non-producing phi 6R strains to the lytic enzyme associated with the phi 6 virion, indicating that they had an altered cell wall structure. The lytic enzyme of phi 6, needed both in penetration and progeny release, was less active on the altered cell wall, leading to diminished infection efficiency and deficient plaque formation.