Scorpion gut microbiomes as a source of bioactive and rare actinobacteria with nonribosomal peptide potential

Actinobacteria are well-known for their ability to produce bioactive secondary metabolites, including nonribosomal peptides (NRPs); however, many host-associated reservoirs remain underexplored. In this study, cultivable actinobacteria were isolated from scorpion gut, including both the intestinal tissue and its luminal contents, and evaluated their antimicrobial activity and presence of NRPs genes. Fifty scorpions (Odontobuthus doriae and Mesobuthus eupeus) were collected from Qom Province, Iran. Dissected gut homogenates were plated on selective media, yielding 120 pure isolates. Taxonomic identification was performed by 16S rRNA gene sequencing, antimicrobial activity was assessed using agar diffusion assays against a broad panel of bacteria and fungi, and isolates were screened for NRPS gene biosynthetic markers by PCR (using A3F/A7R primers). The collection was dominated by Streptomyces, with additional recovery of rarer genera such as Amycolatopsis and Nonomuraea. Overall, 57% of the isolates inhibited at least one test microorganisms, and some strains exhibited specific bioactivity, making them candidates for further investigation. NRPS amplicons (~ 700 bp) were detected in 33.3% of the isolates and were enriched among the 42.6% of bioactive isolates, suggesting a partial association between antimicrobial phenotypes and putative NRP biosynthetic capacity. Five isolates showed < 98.5% 16S rRNA similarity to described species, indicating potential taxonomic novelty. Collectively, these findings support scorpion guts as promising, niche-derived sources of diverse actinobacteria with antimicrobial activity and biosynthetic potential for natural product discovery.