Trifolii Strain Research Articles

Studies on Induced Variation in the Rhizobia. III. Host Range Modification of Rhizobium trifolii by Spontaneous and Radiation-Induced Mutation

Schwinghamer, E. A. (Brookhaven Natl. Lab., Upton, New York.) Studies on induced variation in the rhizobia. III. Host range modification of Rhizobium trifolii by spontaneous and radiation-induced mutation. Amer. Jour. Bot. 49(3): 269–277. Illus. 1962.—Mutant strains capable of nodulating pea seedings ineffectively (incapable of nitrogen fixation) have been obtained from 2 antibiotic-resistant marked strains of Rhizobium trifolii which normally do not form nodules on this host. Such variant forms apparently occur spontaneously in these strains at a low frequency which can be significantly increased by irradiation with ultraviolet light, X rays, and fast neutrons. Nodulation of vetch, sweet peas and several varieties of peas by the mutant strains suggests a close parallelism of the extended host range with the range of R. leguminosarum, although nitrogen fixation by the mutants on the new hosts is negligible or absent. The mutant nodules on these hosts also differ from those of the pea strains in slightly smaller size, spherical form, and lighter pink color. Nodule morphology on the homologous host, clover. appears unaltered but a slight loss of effectiveness was noted on red clover. This loss may be attributed partly to a reduction in infective ability since the average number of nodules formed per plant of clover or pea is appreciably lower than for comparable inoculation by strains of nonmutant R. trifolii or R. leguminosarum, respectively. Cultural characteristics of mutant strains resemble those of the nonmutant R. trifolii strains.

STUDIES ON INDUCED VARIATION IN THE RHIZOBIA. III. HOST RANGE MODIFICATION OF RHIZOBIUM TRIFOLII BY SPONTANEOUS AND RADIATION‐INDUCED MUTATION

Schwinghamer, E. A. (Brookhaven Natl. Lab., Upton, New York.) Studies on induced variation in the rhizobia. III. Host range modification of Rhizobium trifolii by spontaneous and radiation‐induced mutation. Amer. Jour. Bot. 49(3): 269–277. Illus. 1962.—Mutant strains capable of nodulating pea seedings ineffectively (incapable of nitrogen fixation) have been obtained from 2 antibiotic‐resistant marked strains of Rhizobium trifolii which normally do not form nodules on this host. Such variant forms apparently occur spontaneously in these strains at a low frequency which can be significantly increased by irradiation with ultraviolet light, X rays, and fast neutrons. Nodulation of vetch, sweet peas and several varieties of peas by the mutant strains suggests a close parallelism of the extended host range with the range of R. leguminosarum, although nitrogen fixation by the mutants on the new hosts is negligible or absent. The mutant nodules on these hosts also differ from those of the pea strains in slightly smaller size, spherical form, and lighter pink color. Nodule morphology on the homologous host, clover. appears unaltered but a slight loss of effectiveness was noted on red clover. This loss may be attributed partly to a reduction in infective ability since the average number of nodules formed per plant of clover or pea is appreciably lower than for comparable inoculation by strains of nonmutant R. trifolii or R. leguminosarum, respectively. Cultural characteristics of mutant strains resemble those of the nonmutant R. trifolii strains.

Lysogeny in Rhizobium trifolii.

A phage-like particle (phage i) found in filtrates of Rhizobium trifolii (strain RT 9) did not produce plaques but induced development of two different phages in a presumed defective lysogenic strain (RT 10). These induced phages (phages 9 and 10) differed in their host ranges and produced plaques on strains RT 9 and RT 10, respectively. Phages 9 and 10 were closely related serologically and were distinct from phage i. Although ultraviolet irradiation resulted in the lysis of RT 10, no free phage was detectable in such lysates. Phage i particles had morphological, chemical, and physical properties similar to those of functional Rhizobium phages but did not produce plaques on any of 12 R. trifolii strains tested. Development of phage i could be induced with ultraviolet irradiation or by treatment with mitomycin C.