PHYSIOLOGICAL STUDIES ON RHIZOBIUM

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Abstract
Exps. were conducted to study the effect, on growth of R. leguminosarum, of N added as NH4Cl, NaNO3, urea, alanine, and bacto-yeast extract. Effects were interpreted from changes in rate of O consumption, as measured by the Warburg micro-manometric technic. In the yeast-extract medium, growth of Rhizobium was greatly stimulated, and almost in direct proportion to amount of extract added. In media containing the other nitrogenous compounds, there was no marked stimulation of growth, irrespective of concentration of N, and presumably the cells remained in the resting state throughout the exp. Although the exact cause of stimulation by yeast extract is unknown, it is possible that the particular form or combination of N in the yeast extract is especially suitable for use by Rhizobium or that stimulation was induced by energy-furnishing ma-terial, accessory food constituents, or by certain elements necessary for growth of the organisms, which were not supplied in the basic medium.