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SUMMARY : Two serologically unrelated strains of nodule bacteria produced two different polysaccharides, only one of which precipitated with antiserum to its parent bacterium. Both polysaccharides interfered with the multiplication of two bacteriophages in liquid cultures of the two bacterial strains, each of which was susceptible to only one of the two bacteriophages. One polysaccharide was slightly more effective than the other in interfering with multiplication of both bacterio- phages; one phage was much more susceptible than the other to the interfering action of both polysaccharides. Crystallized pancreatic ribonuclease interfered with multiplication of bacteriophages much more strongly than did the polysaccharides. Xeither the polysaccharides nor ribonuclease destroyed the phage particles. The chance that a bacteriophage particle will multiply in a liquid culture of Rhizobium bacteria decreases with increasing age of the culture (Kleczkowski & Kleczkowski, 1951). This can have various causes. Bacteria may become increasingly resistant to infection as their cultures age, or some metabolic products accumulating in the medium might interfere with phage activity. The literature contains many references suggesting that polysaccharides, or materials containing polysaccharides, produced by individual bacterial species specifically interfere with the activity of bacteriophages that attack those species (Levine & Frisch, 1933; Burnet, 1934; Gough & Burnet, 1934; White, 1936; Miller & Goebel, 1949). Some authors have also related polysaccharides capable of interfering specifically with bacteriophages to those that confer serological specificity to their host bacteria (see Burnet, Keogh & Lush, 1937). On the other hand, Ashenburg, Sandholzer, Scherp & Berry (1940) found no evidence for specific inhibition of activity of bacteriophage by a polysaccharide produced by its host bacteria, for polysaccharides of widely different origins inhibited similarly. Some polysaccharides have been found to interfere with the multiplication of certain animal viruses in the allantoic sac of the chick embryo (Green & Wooley, 1947; Ginsberg, Goebel & Horsfall, 1948) and with infectivity of plant viruses (Takahashi, 1942, 1946; Bawden & Freeman, 1952). There is no evidence of any specificity in the action of polysaccharides against individual viruses, but different plants differ in the degree to which their susceptibility is influenced (Bawden & Freeman, 1952). The work described in the present paper was done to see whether strains of Rhizobium bacteria that differ serologically and in their susceptibility to different bacteriophages, produce different specific polysaccharides and, if so, whether these are active serologically and act specifically against a bacterio- phage to which the species is susceptible.

Effect of Specific Polysaccharides from the Host Bacteria and of Ribonuclease on the Multiplication of Rhizobium Phages