Effects of mixed culture fermentation of Bacillus amyloliquefaciens and Trichoderma longibrachiatum on its constituent strains and the biocontrol of tomato Fusarium wilt

In this study, an in vitro antifungal growth experiment showed that the inhibitory rate of the MCF broth on pathogenic fungi (Fusarium oxysporum f. sp. lycopersici, Botrytis cinerea, Trichothecium roseum, and Colletotrichum gloeosporioides) was less than that of B. amyloliquefaciens culture fermentation (BCF). Moreover, the content and gene expression of lipopeptide antibiotics was also lower than that in the BCF group. However, the pot experiments based on irrigation with appropriately diluted fermentation broth showed that the biocontrol effect of MCF on tomato Fusarium wilt was significantly higher than that of TCF (T. longibrachiatum culture fermentation) and BCF, and was approximately 15.79% higher than that of the BTF group which made by mixing equivalent amounts of BCF and TCF. In MCF broth, two microorganisms antagonized and coexisted, and the growth of T. longibrachiatum was inhibited. Using transcriptomic methods, we speculated that MCF can up-regulate the expression of genes related to carbon and nitrogen metabolism, oxidation–reduction activity, sporulation, environmental information response and chemotaxis, and biosynthesis of secondary metabolites of B. amyloliquefaciens, which might enhance the nutrient substances metabolism and competitiveness, survival ability, colonisation, and adaptability to the environment to increase its biocontrol potential. In order to explore the possible mechanism of changes in the biocontrol activity of tomato Fusarium wilt of the mixed culture fermentation (MCF) of Bacillus amyloliquefaciens and Trichoderma longibrachiatum compared with that of monoculture fermentation of B. amyloliquefaciens (BCF), the fresh cell-free filtrates of culture fermentation of the BCF and MCF groups were mixed with the sterile fresh medium to a final concentration of 75% (v/v). Each treatment was inoculated with 2% of the activated B. amyloliquefaciens spore suspension. The cultures were incubated at 30 ± 2 ℃ and shaken at 150 rpm for 24 h. Sample cells were harvested by centrifugation (10,000 g, 4 ℃), washed with sterile water, and then centrifuged and stored in liquid nitrogen immediately. The sample cells were sent to Novogene Bioinformatics Technology Co., Ltd. (Tianjin, China) for transcriptome sequencing.