Antimicrobial and Antioxidant Activities of Endophytic Fungi Associated with Arrabidaea chica (Bignoniaceae)

**Background:** Endophytic fungi are microorganisms that live within plant tissues without causing harm and are known to produce diverse bioactive secondary metabolites. The Amazonian medicinal plant Arrabidaea chica (Bignoniaceae) has documented antimicrobial, anti-inflammatory, and antioxidant properties, but its endophytic fungal community had not been previously explored for biotechnological potential. This study aimed to evaluate the antimicrobial and antioxidant activities of metabolites produced by endophytic fungi isolated from the leaves and branches of A. chica.

**Methods:** A total of 107 endophytic fungi were isolated from surface-sterilized leaves and branches of A. chica collected in February 2019 from Embrapa Western Amazon, Brazil. Fungi were grown in liquid potato dextrose medium supplemented with yeast extract and NaCl under static conditions at 30°C for 14 days. Metabolites were extracted with ethyl acetate, and crude extracts were tested for antimicrobial activity using the microdilution method with resazurin (bacteria) and TTC (fungi) reduction. Initial screening was performed against Staphylococcus aureus, Escherichia coli, and Candida albicans; active extracts were further tested against a panel of 11 additional pathogens. Minimum inhibitory concentrations (MICs) were determined for active extracts. Antioxidant activity was assessed using the DPPH radical scavenging assay (EC50 determination) and the ferric reducing antioxidant power (FRAP) method. Chemical profiling of the most promising extracts was performed using thin-layer chromatography (TLC) with specific developers, and total phenolic content was measured using the Folin-Ciocalteu method. The most promising fungi were identified by classical taxonomy and molecular sequencing of ITS, β-tubulin, and calmodulin loci.

**Key Results:** Of the 107 fungal extracts, 18 showed antimicrobial activity against at least one test strain. The fungus CF2-13, isolated from leaves and identified as Botryosphaeria mamane (99% maximum likelihood), exhibited the broadest antimicrobial spectrum, inhibiting Gram-positive (S. aureus, S. epidermidis, B. subtilis) and Gram-negative (E. coli, P. mirabilis, K. pneumoniae, S. marcescens, S. enterica) bacteria, as well as fungi (C. albicans, C. tropicalis, C. parapsilosis, A. brasiliensis). The lowest MIC was 0.312 mg/mL against S. aureus and C. parapsilosis. For antioxidant activity, 70 extracts showed >70% DPPH scavenging at 10 mg/mL. The fungus CG1-7, isolated from branches and identified as Colletotrichum sp. (82% maximum likelihood as C. siamense), had the lowest EC50 of 11 µg/mL, comparable to quercetin (8 µg/mL). Seven extracts had EC50 <1000 µg/mL. FRAP results confirmed antioxidant potential, with 20 extracts showing 166.0–218.6 μmol TE/g. TLC revealed terpenes and flavonoids in both active extracts; phenolic compounds were detected in CF2-13. Total phenolic content was 3.70 mg GAE/100 mg for CF2-13 and 5.28 mg GAE/100 mg for CG1-7.

**Clinical Implications:** This is the first report on the bioactivity of endophytic fungi from A. chica. The strong antimicrobial activity of B. mamane CF2-13, especially against S. aureus and C. parapsilosis, suggests potential for developing new antimicrobial agents, particularly given rising antibiotic resistance. The antioxidant activity of Colletotrichum sp. CG1-7, equivalent to quercetin, indicates promise for nutraceutical or cosmetic applications. Further studies are needed to isolate and characterize the specific bioactive compounds and to optimize fermentation conditions for large-scale production.