Differential stimulation and inhibition of growth of Rhizobium trifolii strain T1 and other Rhizobium species by various carbon sources.

The physiological properties of Rhizobium trifolii strain T1 were studied in detail, since this strain has many useful characteristics and appears ideal for development as a reference strain for R. trifolii. Some tricarboxylic acid cycle intermediates and related compounds were found to stimulate growth in the presence of sucrose and arabinose, while others inhibited growth partially or completely. Other R. trifolii strains behaved likewise. Moreover, similar responses were also observed with other Rhizobium species, both fast-growing and slow-growing. On the basis of these growth responses, the various species of fast-growing and slow-growing rhizobia could be differentiated. Of the fast-growers tested, R. trifolii and R. leguminosarum are much more closely related to each other than either is to R. meliloti. Similarly, the slow-growing cowpea rhizobia are more closely related to R. japonicum than either group is to R. lupini. It is proposed that strain T1 should be developed as the reference strain for Rhizobium trifolii.