Biotin as a Growth Factor for Rhizobia

Abstract

The preparation of synthetic media containing salts and carbohydrates which have been purified to insure that they are free from biotin is described. Cultures of Rhizobium trifolii, R. meliloti, and R. leguminosarum have been transferred continuously in these purified media without decrease in growth. Media containing synthetic glycerol as the source of carbon were found to support growth of rhizobia through continuous transfer. The growth in these media was found to be independent of the level of sugar or glycerol or the number of transfers. Data are presented to show that any impurities of biotin in the carbohydrate were present in smaller quantities than will stimulate the growth of rhizobia. In all the continuous transfer expts. in the purified media, the max. growth was only about 1/10 that obtained with a complete medium, i.e., one to which the optimum quantity of biotin was added. Attempts to demonstrate synthesis of biotin by one strain of R. trifolii have been unsuccessful. A strain of R. leguminosarum which is not stimulated by biotin synthesized only one [gamma] of biotin to 8 liters of purified medium.