La biosynthèse de l'acide indolyl‐3‐acétique en liaison avec le métabolisme du tryptophol et de l'indolyl‐3‐acétaldéhyde chez Rhizobium

Several indolic compounds are formed when tryptophan or tryptamine is metabolized by Rhizobium. Among these are indole‐3‐acetaldehyde (IAAld), tryptophol (Tr‐ol), and indole‐3‐acetic acid (IAA). The metabolic relationship among the three compounds was investigated. The experiments were carried out either in the culture medium of growing Rhizobium cultures or in suspensions of washed bacterial cells. In neither case Tr‐ol would function as a precursor of IAA, but tryptophan‐2‐14G gave rise to the formation of both IAA and Tr‐ol. The ratio of IAA to Tr‐ol depended on the experimental conditions, shaking favoring the formation of IAA. Also IAAld gave rise to the formation of IAA and Tr‐ol when incubated with suspensions of washed cells. The ratio of the two compounds depended on experimental conditions such as pH value and shaking, the latter reducing the formation of Tr‐ol. These results cannot be explained by the assumption of a dismutation mechanism catalyzed by a single enzymatic unit. The operation of two enzyme systems, responsible for the reduction and the oxidation, respectively, of IAAld is suggested and discussed.