Actinobactérias do bioma caatinga: atividade anti-MRSA e caracterização de uma nova espécie de Streptomyces

Abstract

Antimicrobial resistance (AMR) is recognized by the World Health Organization as one of the greatest global health threats. The emergence and spread of multidrug-resistant microorganisms, such as methicillin-resistant Staphylococcus aureus (MRSA), intensify the urgency for the discovery of new bioactive compounds. In this context, actinobacteria of the genus Streptomyces represent one of the main microbial sources of natural antibiotics, historically accounting for more than two-thirds of clinically used antibiotics. Extreme and unexplored environments, such as the Caatinga biome, constitute potential reservoirs of microbial strains capable of producing novel secondary metabolites. This study aimed to isolate actinobacteria from Caatinga soil samples, followed by morphological, genomic, metabolomic, and functional characterization of promising strains with antimicrobial activity. Soil samples were subjected to thermal pretreatment and selective cultivation on media such as soil agar and water agar, resulting in the recovery of 340 actinobacterial isolates. Metabolomic analysis by LC-MS mass spectrometry, combined with data annotation using GNPS and ClassyFire, revealed the presence of compounds of interest, including signaling molecules, antitumor agents, and antibacterial metabolites. Many detected ions were classified as "no match", suggesting the presence of potentially novel metabolites. One of the isolates, coded as I007 and highlighted for its antimicrobial activity, exhibited filamentous morphology, Gram-positive staining, and structural features typical of actinobacteria, as observed under scanning electron microscopy. Whole-genome sequencing of isolate I007, followed by genome assembly, revealed a genome size of 8.03 Mbp with a GC content of 72.4%. Bacterial identification through phylogenomic analyses indicated that isolate I007 represents a new species of the genus Streptomyces. In silico analysis of biosynthetic gene clusters using the antiSMASH 5.0 tool identified 47 biosynthetic regions, including pathways for NRPS, type I, II, and III PKS, terpenes, siderophores, melanin, butyrolactones, lantipeptides, alkaloids, and ectoine, demonstrating its high metabolic potential. Functional screening revealed antimicrobial activity against MRSA, with a 9.3 mm inhibition halo for fraction A1, indicating the production of compounds active against multidrug-resistant pathogens. Thus, the Caatinga represents a promising environment for microbial bioprospecting. Streptomyces sp. I007, by combining genetic potential and functional activity, emerges as a strong candidate for future studies focused on purification, structural characterization, and pharmacological application of new antibiotics. This study contributes to advancing knowledge of the microbial biodiversity of the Caatinga and its application in the discovery of innovative antimicrobial agents.