Phage pilH alpha: a phage which adsorbs to IncHI and IncHII plasmid-coded pili.

Phage pilH alpha was specific for bacterial strains, of various genera, harbouring plasmids of the HI and HII incompatibility groups. Plaque formation was temperature sensitive in that plaques formed at 26 degrees C but not at 37 degrees C. Plaques were fairly clear, irregular in outline and varied from pin point to about 2 mm in diameter on all hosts where plaques were detected. The phage had an isometric hexagonal outline with a diameter of 25 nm. It contained RNA but differed from all but one other plasmid-dependent RNA phage by being sensitive to chloroform. It adsorbed along the length of the shafts of IncHI and HII plasmid-coded pili.