ANTIBACTERIAL ACTIVITY AND VIRULENCE FACTORS INHIBITION BY Xylaria sp. (Xylariaceae, Ascomycota): A STUDY OF BIOACTIVE POTENTIAL

Background: The genus Xylaria comprises over 300 fungal species distributed worldwide that exhibit adaptability to various ecological roles. Consequently, their potential for the synthesis of bioactive molecules with antibacterial and antivirulence properties has been reported. Objective: To characterize the antibacterial and antivirulence properties of Xylaria sp. (OG-03) strain against phytopathogenic bacteria (Pseudomonas syringae, Pseudomonas syringae pv. tabaci, Pseudomonas putida, and Chryseobacterium sp.) and Chromobacterium violaceum 553, respectively. Methodology: A fungal strain was isolated and characterized morphologically and molecularly, and its evolutionary history was investigated through phylogenetic reconstruction. Mycelial growth was assessed in different culture media with natural substrates, and fungal extracts were obtained to evaluate minimal inhibitory (phytopathogenic bacteria) and antivirulence (biosensor strain) activities. Results: Morphological and molecular characterizations of the fungal strain suggested an indeterminate taxonomic classification at the species level within the genus Xylaria. The highest mycelial growth was observed in the REA culture medium, and the liquid rice extract promoted ectostomes proliferation. Fungal biomass extracts displayed antibacterial activity against P. syringae (MIC 7.81 µg/mL, 88% inhibition), Pseudomonas syringae pv. tabaci (MIC 1.95 µg/mL, 87% inhibition), Pseudomonas putida (MIC 1.95 µg/mL, 79.25% inhibition), and Chryseobacterium sp. (MIC 7.81 µg/mL, 85.03% inhibition), respectively. Antivirulence against C. violaceum reduced biofilm formation (125 µg/mL, 59% inhibition) and violacein production (62.5 µg/mL, 58% inhibition). Implications: Xylaria sp. exhibits antibacterial and antivirulence activity against phytopathogenic bacteria. Conclusions: The strain studied is suggested to be an undetermined taxon within the genus Xylaria. The results of biological assays indicated that the fungus possesses antibiotic properties against phytopathogenic bacteria and can inhibit virulence factors associated with quorum sensing.