Synthesis mechanism of antifungal active protein in the fermentation of agar waste liquid by Streptomyces rubiginosoheloolus.

Phytopathogenic fungi represent a serious threat to global crop production, food security, and public health. Agar waste liquid as a biomass-rich byproduct, shows great potential for bioconversion into value-added antifungal compounds through microbial fermentation processes. This study demonstrated that fermentation of agar waste liquid by Streptomyces rubiginosoheloolus significantly enhanced antifungal activity, with the 50 % waste liquid group exhibited inhibition rates of 59.7 % and 57.1 % against Alternaria alternata and Alternaria spp. (MICs of 0.98 and 3.90 μg/mL), respectively. Metabolomic analysis revealed that upregulated glycolysis and TCA cycle energized antifungal protein synthesis, while enhanced amino acid metabolism promoted protein formation. Key antifungal proteins (histone-like nucleoid-structuring protein H-NS, hypothetical protein and ribosomal protein) were identified by ammonium sulfate precipitation, anion-exchange chromatography and MS. These proteins disrupt fungal membranes via hydrophobic interactions, causing ROS accumulation and lipid peroxidation. The study provided theoretical basis for microbial fermentation-derived antifungal agents and seaweed gum waste valorization.