Identification of postharvest fruit biocontrol strain Burkholderia contaminans against fungi decay

Abstract

Botrytis cinerea (gray mold) infection can cause postharvest quality decline of various fruits, resulting in huge economic losses. The use of fungicides to maintain fruit quality will lead to potential environmental pollution, harming human health. Biocontrol using beneficial microorganisms has been successfully applied to control postharvest diseases of fruits. In the present study, bacterial strain B-1 with a high antifungal activity against Botrytis cinerea was isolated from the surface of apricots. Combining morphological and biochemical characterization with 16S rDNA and recA gene sequencing, this bacterial strain was identified to be Burkholderia contaminans, which is a kind of B. cepacia complex (Bcc). In order to further reveal its antifungal mechanism, the bacterial cells were lysed, and a protein with antifungal activity was isolated by DEAE-52 ion-exchange chromatography and sephadex G-100 gel filtration chromatography. The purified protein with a molecular weight of 17.5 kD was analyzed by mass spectrometry and retrieved from ncbiprot database, and was determined to be as superoxide dismutase. The bacterial protein could effectively inhibit mycelia growth of B. cinerea, Penicillium expansum, and Alternaria tenuissima in vitro. The protein exhibited a broad-spectrum antifungal activity against nine pathogenic fungi. Moreover, it could significantly inhibit the occurrence of postharvest cinee mildew in grape and strawberry fruits. After six days of inoculation with antifungal crude protein, the inhibition rates of grape and strawberry fruits were 88.97% and 86.55%, respectively. In addition, it could affect the DNA level, reactive oxygen species and mitochondrial membrane potential in pathogenic fungi. This study demonstrated that the B. contaminans B-1 strain had a great potential to be used a biocontrol microorganism to protect against postharvest fruit fungal decay.