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Tryptophan has long been known as an essential amino acid for many forms of life. However, nuimerous microorganisms do not require nitrogen in the form of tryptophan, and several nitrogenous compounds are known which replace the nutritional requirement for tryptophan. The demonstration that anthranilic acid (Snell, 1943) or indole (Schweigert et al., 1946) supports growth of Lactobacillus arabinosus in the absence of tryptophan suggests the existence of an anthranilic acid -* indole -÷ tryptophan pathway of synthesis. Such a metabolic pathway has been described in Neurospora (Tatum and Bonner, 1943; Tatum, Bonner, and Beadle, 1943), and cell-free extracts of Neurospora sitophila form tryptophan in the presence of indole, serine, and pyridoxal phosphate (Umbreit, Wood, and Gunsalus, 1946). Since serine stimulates the growth of L. arabinoms in the presence of indole (Schweigert, 1947), it has been concluded (Rydon, 1948; Work and Work, 1948) that, as in Neurospora, indole is condensed with serine to yield tryptophan by this organism and, moreover, that anthranilic acid is probably the precursor of indole. Thus, essentially by analogy, the apparent pathway of tryptophan synthesis in Neurospora has been claimed to exist in bacteria. This study was initiated to clarify the biochemical steps leading from anthranilic acid to tryptophan in L. arabinosus. The growth supporting capacity of a series of potential intermediates along the pathway of anthranilic acid bioconversion was tested, and conditions for the utilization of anthranilic acid and indole were studied. The tryptophan content of cells grown in the presence of anthranilic acid, indole, or tryptophan was also determined. The results appear to cast doubt upon the simple metabolic pathway of anthranilic acid conversion to tryptophan previously described.

THE ROLE OF ANTHRANILIC ACID IN THE NUTRITION OF LACTOBACILLUS ARABINOSUS