Biofilm: New insights in the biological control of fruits with Bacillus amyloliquefaciens B4.

Biofilms are sessile microbial communities growing on surfaces, which are encased in some self-produced extracellular material. Beneficial biofilm could be widely used in agriculture, food, medicine, environment and other fields. As an ideal biocontrol agent, Bacillus amyloliquefaciens B4 can form a strong biofilm under static conditions. In this study, we screened out metal compounds that enhanced or inhibited the biofilm formation ability of B4, established the relationship between the biofilm of B4 strain and its postharvest biocontrol effect, and explored the regulation of metal compounds on the biofilm formation. The results showed 0.5 mmol L-1 ferric chloride could enhance the biofilm formation and strengthen the antifungal effect of B4, indicating that there was a positive relationship between the growth of biofilm and its biocontrol effect. The enhanced biofilm had a certain biocontrol effect on different fruit, including peach, loquat, Kyoho grape and cherry tomato. Furthermore, the expression of degU and tasA was affected by metal ion treatment, which meant the genes might be essential for the biofilm formation of B4. Our findings suggested that biofilm of B. amyloliquefaciens played an essential role in the process of biocontrol and it might be a novel strategy for managing postharvest fruit decay.

Antifungal Activity of Volatile Organic Compounds Produced by Bacillus methylotrophicus and Bacillus thuringiensis against Five Common Spoilage Fungi on Loquats.

Loquat fruit is one of the most perishable fruits in China, and has a very limited shelf life because of mechanical injury and microbial decay. Due to an increasing concern about human health and environmental security, antagonistic microorganisms have been a potential alternative for fungicides to control postharvest diseases. In this work, the antifungal effect of volatile organic compounds (VOCs) produced by Bacillus methylotrophicus BCN2 and Bacillus thuringiensis BCN10 against five postharvest pathogens isolated from loquat fruit, Fusarium oxysporum, Botryosphaeria sp., Trichoderma atroviride, Colletotrichum gloeosporioides, and Penicillium expansum were evaluated by in vitro and in vivo experiments. As a result, the VOCs released by BCN2 and BCN10 were able to suppress the mycelial growth of all targeted pathogens according to inhibition ratio in the double petri-dish assay as well as disease incidence and disease diameter on loquat fruits. The main volatile compounds were identified by solid-phase microextraction (SPME)-gas chromatography. These VOCs produced by the two strains played complementary roles in controlling these five molds and enabled loquat fruits to keep fresh for ten days, significantly. This research will provide a theoretic foundation and technical support for exploring the functional components of VOCs applicable in loquat fruit preservation.