Abstract
Beneficial microorganisms to control bacterial diseases has been widely used in aquaculture, Bacillus amyloliquefaciens (BaX030) as a probiotic feed additive was a commonly biological control method. Added sucrose promoted the growth of BaX030, and the yield of its antibacterial substance macrolactin A was enhanced by 1.46-fold. A total of 2055 proteins were screened through proteomics, with 143 upregulated and 307 downregulated. Differential protein expression analysis and qRT-PCR verification showed that the pentose phosphate pathway and the fatty acid synthesis pathway were upregulated, thereby providing sufficient energy and precursors for the synthesis of macrolactin A. The influence of some potential regulatory factors (SecG, LiaI, MecG and ComG) on macrolactin A was discovered. After grass carp were fed with BaX030, the abundance of probiotics (Fusobacterium, Proteobacteria, Gemmobacter) were higher than the control group, and the abundance of potential pathogenic bacteria (Planctomycetes, Aeromonas) were significantly lower than the control group. The cell and challenge experiments showed that BaX030 can significantly increase the expression of C3 and IL8 in the liver and kidney, which decreases the risk of immune organ disease. Moreover, BaX030 effectively reduced the mortality of grass carp. The results revealed that BaX030 can significantly improve the structure of the intestinal flora, enhance immunity and it is beneficial to the control of grass carp Aeromonas.
Highlights
The increasing density of fish farming and the deterioration of the aquatic environment have led to disease outbreaks and aquaculture losses
The results showed that the relative abundances of the families Rhodobacteraceae, Nocardioidaceae, Geobacteraceae and Ignavibacteriaceae were significantly higher in the EX group, while the relative abundances of the families Planctomycetaceae, Actinomycetaceae, Verrucomicrobiaceae, and Enterobacteriaceae were significantly increased in the WT group (P < 0.05) (Figure 7B), which suggested that metabolic changes occurred in the intestinal microbiota of grass carp caused by the feeding of B.amyloliquefaciens X030 (BaX030)
Sucrose stimulated bacterial growth, which led to an increase in the production of macrolactin A (Figures 1A, 2A)
Summary
The increasing density of fish farming and the deterioration of the aquatic environment have led to disease outbreaks and aquaculture losses. Systematically mining multiple core genes and proteins has become a research trend; it explains the molecular mechanism underlying the synthesis of secondary metabolites and the increase of their production through genomics combined with transcriptomics, metabolomics or proteomics (Chavali and Rhee, 2018; Xu et al, 2018; Zhao et al, 2018). Proteomics has produced a variety of novel leads for the analysis of protein traffic in Bacillus. These studies proved that the availability of genomics, proteomics and bioinformatics tools can effectively increase the yield of secondary metabolites and modify related gene clusters
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