GC-MS Profiling and In Silico Evaluation of Streptomyces levis Strain RS18 Against Phytopathogenic Fungi

The present study aimed to isolate and evaluate actinobacterial isolates for their antifungal potential against phytopathogenic fungi. A total of 20 morphologically distinct actinobacterial isolates were obtained from soil samples and screened against Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, and Penicillium sp. Among these, isolate RS18 exhibited the highest antifungal activity and was identified as Streptomyces levis based on 16S rRNA gene sequencing. Cultural characterization of this potent strain on various International Streptomyces Project media revealed distinct colony morphologies and pigment production patterns. Response Surface Methodology was employed to optimize the production conditions, and the ethyl acetate extract from the optimized culture demonstrated strong antifungal activity in both well diffusion and minimum fungicidal concentration assays. GC-MS analysis of the crude extract identified multiple bioactive compounds, including esters, alcohols, and nitrogen-containing heterocycles. ADMET analysis of the top compounds indicated high gastrointestinal absorption, non-mutagenicity, good drug-likeness, and predicted hepatotoxicity. Molecular docking studies revealed that 3,8-dimethyl-3-(4-methylpent-3-enyl)-11H-pyrano[3,2-a] carbazole had the highest binding affinity (-5.53 kcal/mol) with the Aspergillus hydrolase protein (1UKC), followed by other compounds with moderate binding energies. These results suggest that the strain S. levis RS18 is a promising biocontrol candidate against fungal phytopathogens and may be beneficial in agricultural practices to enhance crop production in target organisms.