A Characterization of Bacterium radiobacter (Beijerinck and Van Delden) Löhnis

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Abstract
Bact. radiobacter occurs frequently near legume plants and is found associated with the nodule bacteria (Rhizobium spp.); it is also found commonly on plates used for making fresh isolations of Phytomonas tumefaciens and P. rhizogenes, the causative organisms respectively of the crown gall and hairy root diseases of nursery apple trees. Its characteristics were studied, and methods were devised for differentiating it from the nodule bacteria. It consists of motile, gram-negative rods with 1-4 peritrichous flagella. It produces turbidity in broth, and punctiform colonies on gelatin plates; there is no liquefaction. Mannitol agar colonies are white, slimy and spreading. Growth on sugar media of low N-content is good. Starch is not hydrolyzed. Nitrates are completely destroyed, probably due to assimilation by the organism. Temp. of growth is from about 1[degree]C to 45[degree]C with the optimum at about 28[degree]. The organism is aerobic. It produces ELS, and grows well between pH 5 and pH 11.5. Carbon is utilized efficiently with the major portion converted into CO2 and cell substance. Gum is also produced. The special reactions by which the organism may be distinguished from Rhizobium spp. are the browning of glycerophosphate agar; turbidity with heavy ring or pellicle in veal infusion broth, Clark and Lubs" medium, and Koser''s uric acid medium; characteristic colonies on nitrate, glycerol agar; production of H2S in ZoBell''s medium, and tolerance to alkali. Bact. radiobacter shows similarity (and evidently close affinity) to Rhizobium spp.