We isolated a new metabolite, streptonigrone, from the same Streptomyces species that produces fujianmycins A and B. Its structure was defined as the 2-pyridone corresponding to the 2-pyridinecarboxylic acid structure (1) of streptonigrin by comparing physical properties (e.g., insolubility in aqueous sodium bicarbonate versus streptonigrin's solubility, molecular formula C24H22N4O7 versus C25H22N4O8, differing by CO) and spectral data (MS, 1H NMR showing retention of all carbon-bound protons of streptonigrin except for the upfield shift of the 3'-methyl group on ring C, consistent with the 2-pyridone structure). Streptonigrone showed no antimicrobial activity at 50 μg/ml against strains of Streptomyces aureofaciens, S. fragilis, Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae, while streptonigrin inhibited all test organisms at this concentration, indicating the importance of the carboxyl function for such activity. Regarding the biosynthesis of the streptonigrin group of metabolites, the phenylpyridine ring system (present in streptonigrin, streptonigrone, and lavendamycin) is derived biosynthetically from β-methyltryptophans. We proposed a pathway involving the covalent hydration of a β-carboline system bearing two electron-withdrawing substituents (carboxyl and quinolinequinone) adjacent to the electronegative nitrogen of the pyridine ring, followed by 1,6-elimination of the original indole amino group (assisted by protonation) to cleave the center ring and generate the correctly substituted phenylpyridine system. This process parallels the known ring opening of indoles bearing electron-withdrawing substituents.