Function of pili in bacteriophage phi 6 penetration.

The genome of bacteriophage phi 6, which has a lipid protein envelope, consists of three pieces of dsRNA. Virus infection is initiated by attachment to a phi 6-specific host pilus followed by fusion of the phage membrane and the bacterial outer membrane. In this study we analysed several different phi 6 hosts as well as more than 200 independently isolated phi 6-resistant variants derived from Pseudomonas syringae pv. phaseolicola. It is shown that phi 6-specific pili are coded by genes located in the host chromosome. It appears that pilus reaction is needed to pull the pilus-associated virus through the extracellular polysaccharide of the host and thus to bring it into contact with the outer membrane where membrane fusion can take place.