A phage-resistant mutant of Lactobacillus casei which permits phage adsorption but not genome injection.

A phage-resistant mutant of Lactobacillus casei (strain YIT 9021) was capable of adsorbing both PL-1 and J-1 phages, but did not yield phage-infected cells. The mutant and wild-type strains were identical in morphology and sugar composition of the cell walls. Attempts to induce prophages from strain YIT 9021 were unsuccessful. Electron microscopic examination of negatively stained mixtures of phage PL-1 and YIT 9021 bacteria revealed that the phages were adsorbed to the cells in a tail-first orientation. All the absorbed phages had DNA-filled heads. It was concluded that PL-1 adsorbed normally but was blocked in the injection of the phage genome into the cell.