Antifungal mechanism and application to phytopathogenic fungi after anaerobic fermentation of Gracilaria agar wastewater

Agar production is accompanied by a large amount of wastewater, which threatens the ecological environment and wastes biomass resources. The high-value utilization of biomass resources in wastewater is one of the key factors in wastewater treatment. We investigated the conversion process and antifungal mechanism of large molecule polysaccharides in wastewater into small molecule substances with antifungal activity through anaerobic fermentation. The results indicated that anaerobic fermentation of GAW achieved inhibition rates of 91.06 % and 88.94 % against Alternaria alternata and Alternaria spp. 16S rDNA sequencing and metabolomics revealed that dominant species such as Blautia, Agathobacter and Sphingomonas converted polysaccharide into phenolic acids like procyanidin C and columbidin. These substances disrupted the integrity of fungal cells, leading to their death. The preparation of composite antifungal agents using fermentation products effectively inhibited cherry tomato spoilage and toxin production. This study provided reliable technical support for the reuse of seaweed waste resources.