Some bacteriophages active against Rhizobium trifolii strain W19.

Fourteen soil bacteriophages active against Rhizobium trifolii W19 have been studied which fall into four structural groups. Group 1 phages have contractile tails. Some particles show double base plates to which at least three spikes are attached, and fibers are attached to the base plates. Group 2 phages also have contractile tails. At least five spikes are attached to the base plate, and there are spherical bodies adjacent to the tail, at the ends of fibers attached to the tail base. Group 3 phages have contractile tails, but are larger than phages of groups 1 and 2. The end of the tail has a complex structure. Group 4 phages have long, noncontractile tails. Phages c and I of group 1 and phages a and e of group 2 were chosen for further study. Single-step growth curves were plotted, and absorption constants were measured. The classification into groups was confirmed by using antiserum inactivation. Susceptibility of phage-resistant mutants of R. trifolii W19 to these bacteriophages was determined.