Some effects of medium composition and metabolic intermediates on biotin inhibition in a strain of Rhizobium japonicum.

Abstract

Growth of Rhizobium japonicum No. 508 in a mineral salts – mannitol medium with 0.01 M NH4Cl and 0.2 g/l casein hydrolysate as nitrogen sources was inhibited by as little as 0.001 μg/l biotin. When 0.01 M NH4Cl and 0.2 g/l glutamic acid were the nitrogen sources, biotin inhibited growth at a concentration of 0.1 μg/l. Growth inhibition by biotin was observed in various defined media. When vitamin-free casein hydrolysate was the organic nitrogen source, there was slightly less inhibition. However, the degree of inhibition remained independent of the casein concentration. Additions of amino acids did not affect the inhibition. The effect was minimal when the organism was grown in medium containing undefined yeast extract even in the presence of added biotin. In such medium, growth was stimulated by the addition of avidin. When biotin was added to an actively growing culture, no inhibition occurred. If the biotin was removed from an inhibited culture, growth was reestablished. In media containing α-ketoglutarate, biotin did not inhibit growth of the organism, and with succinate, biotin was slightly stimulatory.