Barbaloin stimulates growth of Eubacterium sp. strain BAR, a barbaloin-metabolizing bacterium from human feces

Eubacterium sp. strain BAR, isolated from human feces, transformed barbaloin to aloe-emodin anthrone in a basal medium lacking carbohydrate. Barbaloin remarkably stimulated the growth of strain BAR in the basal medium, the stimulative extent of the growth depending on the amount of barbaloin added. The addition of D-glucose, D-galactose, maltose, cellobiose, sucrose or D-amygdalin to the basal medium containing barbaloin caused a decrease of the growth stimulated by barbaloin to the growth level with each sugar, resulting in a complete inhibition of the barbaloin transformation. On the other hand, the addition of D-fructose, which itself stimulated the growth of strain BAR, further increased the growth in the presence of barbaloin and little inhibited barbaloin transformation. Nojirimycin bisulfite, a specific inhibitor of glucosidases, potently inhibited the growth with barbaloin, but did not affect the growth with glucose or cellobiose. Also, nojirimycin bisulfite completely inhibited the transformation of barbaloin to aloe-emodin anthrone. These results indicate that a unique enzyme capable of cleaving the C-glycosyl bond is induced in strain BAR by barbaloin and, consequently, strain BAR grows by utilizing as a nutrient the carbohydrate liberated from barbaloin. It is further suggested that the barbaloin-cleaving enzyme is inhibited by nojirimycin bisulfite and that the induction of the enzyme is repressed with D-glucose and D-galactose.