Physiological Studies on Rhizobium

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Abstract
The respiration and growth of representative strains of R. meliloti and R. japonicum as a function of the pH of the medium were measured by the Warburg manometric techninue. The growth of R. meliloti in glucose yeast extract media decreased from a maximum at pH 7.0 to zero at pH 4.6-4.9 in the acid and at pH 9.6 in the alkaline range. Growth of R. japonicum in arabinose-yeast extract media decreased from a max. at pH 6.7-6.9 to zero at pH 4.2 and 9.5. The initial rate of respiration for the 2 spp. reached a maximum at pH 7.2-8.0 and decreased to a very small value at the critical pH for the respective organisms. In both cases the opt. reaction for respiration was more alkaline than that observed for growth. Since the respiration of the 2 spp. responded almost identically to changes in the reaction of the medium, there is probably a close relationship in their respiratory mechanisms.

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