The niacin-tryptophan relationship in the metabolism of Xanthomonas pruni.

The investigations of Starr (1) demonstrated that Xunthomonas pruni requires an exogenous source of nicotinic acid when grown on a medium containing vitamin-free, acid-hydrolyzed casein, methionine, or glutamic acid to provide an organic form of nitrogen. Preliminary work in this laboratory showed that tryptophan could replace nicotinic acid for growth in a similar medium. This was the first known demonstration of a relationship between these compounds in the metabolism of a bacterium. Recently Jakoby et al. (2) have noted that a nicotinic acid-requiring pseudomonad grows very slowly with tryptophan or anthranilic acid. The long list of proposed biological precursors of nicotinic acid has resulted largely from the studies of a number of mutants of Neurospora crassa. There are still a number of unexplained findings (3), but there is good evidence for the precursor role of tryptophan in nicotinic acid synthesis which has also been established in animals fed isotopically labeled tryptophan (4). Kynurenine (5), 3-hydroxyanthranilic acid (6), and quinolinic acid (7) support the growth of rats receiving low tryptophanniacin diets, and kynurenine (8) and 3-hydroxyanthranilic acid (7, 9) cause increased N’-methylnicotinamide excretion. Further studies of the possible r61e of quinolinic acid as an intermediate between S-hydroxyanthranilic acid and nicotinic acid conducted with Neurospora mutants have shown that quinolinic acid is accumulated by the mutant strain 3416 (7, 10) and is utilized to a limited extent by mutant 4540 (7). The results reported below show that anthranilic acid, indole, tryptophan, kynurenine, 3-hydroxyanthranilic acid, or quinolinic acid is capable of replacing nicotinic acid or its amide for the growth of X. pruni.