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Pristinamycin I (PI), produced byStreptomyces pristinaespiralis , is a streptogramin type B antibiotic, which contains two proteinogenic and five aproteinogenic amino acid precursors. PI is coproduced with pristinamycin II (PII), a member of streptogramin type A antibiotics. The PI biosynthetic gene cluster has been cloned and characterized. However, thus far little is understood about the regulation of PI biosynthesis. In this study, a TetR family regulator (encoded bySSDG_03033 ) was identified as playing a positive role in PI biosynthesis. Its homologue, PaaR, fromCorynebacterium glutamicum serves as a transcriptional repressor of thepaa genes involved in phenylacetic acid (PAA) catabolism. Herein, we also designated the identified regulator as PaaR. Deletion ofpaaR led to an approximately 70% decrease in PI production but had little effect on PII biosynthesis. Identical to the function of its homologue fromC. glutamicum , PaaR is also involved in the suppression ofpaa expression. Given that phenylacetyl coenzyme A (PA-CoA) is the common intermediate of the PAA catabolic pathway and the biosynthetic pathway ofl -phenylglycine (l -Phg), the last amino acid precursor for PI biosynthesis, we proposed that derepression of the transcription ofpaa genes in a ΔpaaR mutant possibly diverts more PA-CoA to the PAA catabolic pathway, thereby with less PA-CoA metabolic flux towardl -Phg formation, thus resulting in lower PI titers. This hypothesis was verified by the observations that PI production of a ΔpaaR mutant was restored byl -Phg supplementation as well as by deletion of thepaaABCDE operon in the ΔpaaR mutant. Altogether, this study provides new insights into the regulation of PI biosynthesis byS. pristinaespiralis .IMPORTANCE A better understanding of the regulation mechanisms for antibiotic biosynthesis will provide valuable clues forStreptomyces strain improvement. Herein, a TetR family regulator PaaR, which serves as the repressor of the transcription ofpaa genes involved in phenylacetic acid (PAA) catabolism, was identified as playing a positive role in the regulation of pristinamycin I (PI) by affecting the supply of one of seven amino acid precursors,l -phenylglycine, inStreptomyces pristinaespiralis . To our knowledge, this is the first report describing the interplay between PAA catabolism and antibiotic biosynthesis inStreptomyces strains. Considering that the PAA catabolic pathway and its regulation by PaaR are widespread in antibiotic-producing actinomycetes, it could be suggested that PaaR-dependent regulation of antibiotic biosynthesis might commonly exist.

journal of bacteriology

Involvement of the TetR-Type Regulator PaaR in the Regulation of Pristinamycin I Biosynthesis through an Effect on Precursor Supply in Streptomyces pristinaespiralis