Study on the Nocardia seriolae Antagonistic Bacterium in the Gut Microbiota of Micropterus salmoides

The present study investigates the gut microbiota dynamics of <i>Micropterus salmoides</i> during <i>Nocardia seriolae</i> infection and identifies potential probiotic candidates for disease control in aquaculture. We artificially infected <i>M. salmoides</i> with <i>N. seriolae</i> and analyzed the gut microbiota of dying fish, asymptomatic fish during the peak mortality period, and healthy fish. The results showed that <i>N. seriolae</i> infection significantly altered the gut microbiota diversity. Based on analysis of gut microorganisms, we isolated and identified an <i>N. seriolae</i>-resistant <i>Bacillus</i> from the gut of <i>M. salmoides</i>, which was named <i>B. amyloliquefaciens</i> MS05 (BaMS05). BaMS05 demonstrated significant antibacterial activity against <i>N. seriolae</i> and other common pathogens of <i>M. salmoides</i> both in vitro and in vivo. Additionally, BaMS05 could colonize the gut of <i>M. salmoides</i> for at least five days and exhibited a protective effect against <i>N. seriolae</i> infection, reducing cumulative mortality by 40% at the fifth day. This study provides insights into the role of gut microbiota in disease resistance and highlights BaMS05 as a potential probiotic for preventing and controlling <i>N. seriolae</i> infections in aquaculture. Further research will focus on optimizing the application of BaMS05 and verifying its biosafety for practical use in <i>M. salmoides</i> farming.