Identification and characterization of the antifungal proteins from Bacillus velezensis KL-2 to target plant pathogenic fungi

Pathogenic fungal infection is a primary cause of postharvest fruit and vegetable losses. Since the extracellular secretions of some microorganisms display effective antifungal properties, biological control is a potential strategy for managing fungal diseases. In this study, the fermentation broth crude protein from Bacillus velezensis KL-2 was found to have the ability to inhibit the growth of five common postharvest pathogenic fungi, with the strongest inhibitory effect observed on Monilinia fructicola and Alternaria alternata. The potential antifungal proteins were purified by Q Sepharose FF column and DEAE Sepharose FF column, and identified as dihydrolipoamide dehydrogenase (DLD), oxalate decarboxylase (OxDC) and serine proteinase via LC-MS/MS. Heterologous recombination was used to express the DLD and OxDC genes. Recombinant DLD and OxDC exhibited catalytic and antifungal activity, which effectively inhibited the mycelial growth of Monilinia fructicola, with inhibition rates of 37.91% and 38.26%, respectively. Scanning electron microscopy (SEM) showed that DLD and OxDC damaged the integrity of the cell wall of pathogenic fungi. In conclusion, the DLD from B. velezensis KL-2 was newly discovered antifungal protein and had the potential to become the effective antifungal agent. The study clarified the antifungal potential of Bacillus velezensis KL-2 and provided a research basis for the exploration and application of antifungal proteins.