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<p>In aquaculture, biological control of bacterial infections is a promising strategy that, aside from preventing infections, also benefits the host in several ways. In this study, a <i>Bacillus</i> strain FiA2 isolated from the gut of&#xa0;<i>Carassius carassius</i> (crucian carp) exhibited broad spectrums of activity against multiple aquatic bacterial pathogens. The compound with antibacterial activity was successfully separated and identified as oxydifficidin, with a m/z of 559.47. The oxydifficidin retained its activity even after being exposed to high temperatures, ultraviolet light, proteolytic enzymes, chemical reagents, and alkaline and acidic pH. Furthermore, crucian carp, when supplemented with FiA2 in diet, reduced the infection rate (post-challenged survival rate of 45%), increased the total weight gain by 15.87%, and upregulated the mRNA levels of <i>IGF-1</i> and <i>IGF-2</i> (<i>P</i> &lt; 0.05) of muscular tissues. Similarly, the innate immune-related genes in the liver, the spleen, and the head kidney of the fish in the FiA2-supplemented group were significantly upregulated (<i>P</i> &lt; 0.05). In addition, FiA2 modulated the intestinal microbiota, as observed in the FiA2 group of crucian carp; the predominant phyla were <i>Actinobacteriota</i> and <i>Firmicutes</i>, whereas in the control group, <i>Plesiomonas</i> dominated at the genus level. Overall, we conclude that <i>B. velezensis</i> FiA2, a broad-spectrum oxydifficidin-producing strain, resists infection and positively regulates the growth, immunity, and intestinal microbiota of crucian carp and thus can be implemented as a novel probiotic strain for aquaculture.</p>

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Bacillus velezensis FiA2 as an Oxydifficidin-Producing Strain and its Effects on the Growth Performance, Immunity, Intestinal Microbiota, and Resistance to Aeromonas salmonicida Infection in Carassius carassius

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年2月25日

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  • Tahir Ali Khan,
  • He Liangliang,
  • Kotb A. Attia,
  • Shahida Bashir,
  • Xia Ziyuan,
  • Roua A. Alsubki,
  • Jie Rang,
  • Shengbiao Hu,
  • Liqiu Xia

摘要

In aquaculture, biological control of bacterial infections is a promising strategy that, aside from preventing infections, also benefits the host in several ways. In this study, a Bacillus strain FiA2 isolated from the gut of Carassius carassius (crucian carp) exhibited broad spectrums of activity against multiple aquatic bacterial pathogens. The compound with antibacterial activity was successfully separated and identified as oxydifficidin, with a m/z of 559.47. The oxydifficidin retained its activity even after being exposed to high temperatures, ultraviolet light, proteolytic enzymes, chemical reagents, and alkaline and acidic pH. Furthermore, crucian carp, when supplemented with FiA2 in diet, reduced the infection rate (post-challenged survival rate of 45%), increased the total weight gain by 15.87%, and upregulated the mRNA levels of IGF-1 and IGF-2 (P < 0.05) of muscular tissues. Similarly, the innate immune-related genes in the liver, the spleen, and the head kidney of the fish in the FiA2-supplemented group were significantly upregulated (P < 0.05). In addition, FiA2 modulated the intestinal microbiota, as observed in the FiA2 group of crucian carp; the predominant phyla were Actinobacteriota and Firmicutes, whereas in the control group, Plesiomonas dominated at the genus level. Overall, we conclude that B. velezensis FiA2, a broad-spectrum oxydifficidin-producing strain, resists infection and positively regulates the growth, immunity, and intestinal microbiota of crucian carp and thus can be implemented as a novel probiotic strain for aquaculture.