The inhibitory effect of Bacillus amyloliquefaciens L1 on Aeromonas hydrophila and its mechanism

Abstract

Aeromonas hydrophila is an important aquatic pathogen, and the use of probiotics is an alternative way of controlling this bacterium. In this study, we evaluated the bacteriostatic effects of the fermentation broth, supernatant, and broken bacteria of Bacillus amyloliquefaciens strain L1 on A. hydrophila T1, X1, and W1 isolated from different sources. The results demonstrated that B. amyloliquefaciens L1 has a general bacteriostatic effect on A. hydrophila; the main bacteriostatic substance was found in the B. amyloliquefaciens L1 supernatant and was associated with an extracellular product. The effects of the B. amyloliquefaciens L1 supernatant on A. hydrophila W1 were analyzed at the transcriptome level to study the antibacterial mechanism. Six normalized cDNA libraries were constructed using RNA from a control group and the B. amyloliquefaciens L1 supernatant treatment group. A total of 103,491,644 clean reads were obtained. Further analysis identified 828 significantly differentially expressed genes (DEGs, including 434 up-regulated and 394 down-regulated genes) in A. hydrophila W1 after treatment with the supernatant of B. amyloliquefaciens L1. In a KEGG pathway analysis, six KEGG pathways were found to be significantly enriched. Among them, the Ribosome pathway was enriched only by significantly up-regulated DEGs. The other pathways, including the TCA cycle pathway, carbon fixation pathways in prokaryotes, pyruvate metabolism pathway, butanoate metabolism pathway, and oxidative phosphorylation pathway were enriched, mostly by down-regulated genes. Moreover, an ipath analysis showed that the ribosome regulatory pathway was annotated by up-regulated genes. Bacterial chemotaxis and the phosphotransferase system were annotated by down-regulated genes.