Medicinal Plant Rhizospheres as Reservoirs of Aspergillus-Derived Phytochemicals with Antimicrobial and Insecticidal Potential.

The rhizosphere, a dynamic interface shaped by plant root exudates, fosters microbial communities with significant biochemical potential. This study investigated the interplay between soil properties and fungal bioactivity in the rhizospheres of Withania coagulans and Justicia adhatoda in Pakistan. Physicochemical analysis revealed silty loam textures with divergent phosphorus [25.7 vs. 71.5 mg/kg] and potassium [108 vs. 78 mg/kg] levels, alongside near-neutral pH, influencing microbial dynamics. Two fungal isolates, Aspergillus luchuensis and A. flavus, were identified through morphological traits and ITS-region sequencing. Gas chromatography-mass spectrometry [GC-MS] profiling of ethyl acetate extracts uncovered 30 and 25 previously uncharacterized metabolites in A. luchuensis and A. flavus, respectively, including bioactive compounds such as tetradecanoic acid and nonadecane. Bioassays demonstrated broad-spectrum efficacy against multidrug-resistant clinical isolates, with A. flavus exhibiting notable inhibition against Salmonella typhi [31.7 mm zone] and A. luchuensis against Shigella spp. [23 mm]. Both extracts suppressed Lemna minor growth by 70%, indicating phytotoxic potential, and displayed species-specific insecticidal activity, inducing 70% mortality by A. luchuensis against Blattodea and 50% by A. flavus against the same species. These findings underscore the rhizosphere's role as a reservoir of bioactive fungi, with Aspergillus spp. producing metabolites of pharmaceutical and agrochemical relevance. The study highlights the necessity for advanced structural elucidation and ecotoxicological assessments to harness these compounds, advocating integrated approaches combining metabolomics and genomic mining to unlock novel biotechnological applications.