Inhibitory effects of reumycin produced by Streptomyces sp. TPMA0082 on virulence factors of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic human pathogen that causes a wide range of infections. The increasing multidrug-resistance of P. aeruginosa poses a critical challenge for medical care. P. aeruginosa employs virulence factors and biofilms to establish infections in humans and protect itself from environmental stress or antibiotics. These factors are regulated by a quorum sensing mechanism involving multiple regulatory systems that act interdependently through signaling molecules. Therefore, interference with quorum sensing systems can suppress the pathogenicity of P. aeruginosa. In this study, quorum sensing inhibitors were explored from secondary metabolites derived from 111 strains of actinomycetes by targeting the las system, which is thought to be upstream of the quorum sensing cascade in P. aeruginosa. As a result, reumycin was isolated from the culture broth of Streptomyces sp. TPMA0082. Reumycin, a molecule containing a pyrimidotriazine ring, inhibited the binding of the autoinducer to the LasR receptor in the las system, thereby suppressing the production of P. aeruginosa virulence factors, including pyocyanin, rhamnolipids, elastase, motility, and biofilms, without affecting bacterial growth. Toxoflavin, a reumycin derivative with a methyl group at the N1 position, exhibited strong antibacterial activity. Fervenulin, a reumycin derivative with a methyl group at the N8 position, had a negative impact on the logarithmic growth phase of the bacteria and exhibited lower inhibitory activity against virulence factor production compared to reumycin. These findings suggest that the position and number of methyl groups attached to the pyrimidotriazine structure significantly influence its biological activity, exerting distinct effects on quorum sensing inhibition and antibacterial activity.