Genome-guided discovery of tropansamycins: antimicrobial pentaketide ansamycins

• A “cryptic” pentaketide ansamycin gene cluster was activated. • Seven novel pentaketide ansamycins were isolated from Streptomyces . • Compounds 5 and 6 were active against Xanthomonas oryzae and Staphylococcus aureus . • CYP450 enzyme Tpm16 modulates the bioactivity of pathway intermediates. Although ansamycins are clinically important macrolactams, their pentaketide subset exhibits limited biological activities. Genome mining of rhizosphere-derived Streptomyces sp. LR53 uncovered a cryptic pentaketide ansamycin gene cluster ( tpm ). Activation via 3-amino-5-hydroxybenzoic acid (AHBA) feeding, promoter replacement, and deletion of the cytochrome P450 (CYP450) gene tpm16 enabled the discovery of seven novel metabolites, tropansamycins A–G ( 1 – 7 ), establishing the seventh distinct pentaketide ansamycin scaffold. Notably, congeners 5 and 6 , predominantly accumulated in the Δtpm16 mutant, exhibited potent activity against gram-negative pathogenic bacterium Xanthomonas oryzae and gram-positive bacterium Staphylococcus aureus , with MICs ranging from 2 to 8 μg/mL and were toxic to the producer strain cultivated on LB agar medium. This reveals that the CYP450 enzyme Tpm16 functions as a modification enzyme modulating the bioactivity profile of pathway intermediates. These findings not only expand the structural diversity of ansamycins but also highlight the potential of these pathogen-active ansamycins as promising leads.