A novel Streptomyces species producing thiolutin with anti-MRSA activity and insights into its biosynthetic gene cluster

Exploring microbial diversity from extreme environments, combined with targeted strategies, is a promising approach to uncover novel antimicrobial agents. In order to discover compounds with antimicrobial activity, the sulfur-containing antibiotic thiolutin was isolated and identified from strain HMX112 <i>^T</i> using a targeted antibacterial screening strategy. Strain HMX112 <i>^T</i> was isolated from a soil sample collected from the Turpan-Hami Basin in China and was characterized as an actinobacterium. 16S rRNA gene sequence analysis revealed that strain HMX112 <i>^T</i> showed the highest similarity to <i>Streptomyces lateritius</i> CGMCC 4.1427 <i>^T</i> , <i>Streptomyces narbonensis</i> CGMCC 4.1737 <i>^T</i> , and <i>Streptomyces purpureus</i> DSM 43362 <i>^T</i> , with sequence similarities of 98.83, 98.83, and 98.76%, respectively. Whole-genome analysis indicated that the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain HMX112 <i>^T</i> and its closest related type strains were well below the thresholds for novel species delineation (95 and 70%, respectively). Based on polyphasic taxonomic analysis, strain HMX112 <i>^T</i> was confirmed to represent a novel species of the genus <i>Streptomyces</i>, for which the name <i>Streptomyces flavimicrosus</i> sp. <i>nov.</i> was proposed. Based on its observed antibacterial activity against Gram-positive bacteria, the bioactive components of strain HMX112 <i>^T</i> were investigated, resulting in the isolation and identification of the secondary metabolite thiolutin. Antimicrobial assays demonstrated that thiolutin possesses broad-spectrum inhibitory activity, showing MIC values of 16 μg/mL against two MRSA strains and inhibition rates exceeding 70% against nine plant pathogenic fungi at a concentration of 50 μg/mL. Furthermore, the biosynthetic pathway of thiolutin was elucidated through genomic analysis.