Discovery and characterization of a pigment produced by Streptococcus pyogenes

Abstract

ABSTRACT Streptococcus pyogenes is a major human-restricted pathogen capable of both localized and systemic diseases, as well as causing post-infectious acute and chronic rheumatological conditions. Despite its well-documented clinical importance and over a century of extensive research, gaps persist in understanding this pathogen. We report the discovery of a novel pigment produced by S. pyogenes when cultured in a replete, chemically defined medium. Color development accumulates during growth, requires exposure to oxygen, and remains associated with the bacterial cell. Though only 20% of a small strain collection produced the pigment (8 of 40), positive cultures were overrepresented by M1 and M89 serotypes. Given that pigments are critical virulence and fitness determinants in pathogens like Staphylococcus aureus and Streptococcus agalactiae , here we describe initial attempts to characterize S. pyogenes pigment biosynthesis, regulation, and potential benefits to the organism. 20,405 transposon mutants were screened for pigment loss in liquid culture, and we identified 94 independent hits enriched in pathways associated with isoprenoid biosynthesis, purine biosynthesis, guanosine transport, and mixed acid fermentation. Although color development requires oxygen, the extracted pigment did not provide antioxidative activity as compared to non-pigmented extracts. Pigment production was inhibited when the Rgg2/Rgg3 quorum-sensing system was active, though by unknown means. Treatment of RAW-Blue macrophages with the extracted pigment significantly reduced NFκB activation, suggesting a potential anti-inflammatory effect. Overall, this study describes a previously uncharacterized pigment produced by Streptococcus pyogenes and provides insights into its oxygen-dependent production and associated metabolic pathways. SIGNIFICANCE Streptococcus pyogenes is a ubiquitous pathogen responsible for ∼1.8 million severe infections and 500,000 deaths annually. This organism has not been recognized as a pigment-producing bacterium, but here we identify and characterize the production of a previously unreported colorful compound generated when cultured in a chemically defined medium. This finding reveals an underexplored aspect of S. pyogenes biology and raises the question of its contribution to pathogenesis. Given the established roles of microbial pigments in virulence and immune modulation in other pathogens, this work provides a foundation for future investigations into its functional significance and potential as a target for therapeutic or vaccine development.

The authors' abstract, as published at the source. mBio, 2026 · DOI ↗