Isolation and characterization of a bacteriophage tail-like bacteriocin from a strain of Rhizobium

Abstract

Bacterial strain 16-3 spontaneously produces a bacteriocin which inhibits the growth of closely related strain 16-2. Both strains were newly isolated from root nodules of lupines and probably belong to the species Rhizobium lupini. Production of infectious progeny of newly isolated virulent phage 16-2-4 in strain 16-2 is inhibited completely if complexes are bacteriocin-treated during the first half of the latent period. Treatment begun during the second half leads to premature lysis of complexes and inactivates only those progeny phages which were not yet fully matured at the moment of the particle-induced lysis. Examination by electron microscope of the bacteriocin enrichment revealed the presence of particles 123 nm in length which resemble the tails of T-even bacteriophages. Since the particles sediment together with the bactericidal activity in the sucrose gradient and adsorb specifically to bacteriocin-sensitive cells, it is concluded that they are identical with the bactericidal agent. The particles are not found attached to phage heads and cannot self-propagate; they are regarded as incomplete and are named INCO particles. INCO particles consist of a core enveloped by a contractile sheath. One end of the sheath is connected to a baseplate to which six fibers, each 32 nm in length, are attached. These connect the baseplate of an adsorbing particle to the cell surface. Since INCo cores are probably empty, it is concluded that specific adsorption of the particles to the bacterial surface is sufficient to inactive sensitive cells irreversibly.