AUTHOR=Hu Lingfei , Zhao Lingmin , Zhuang Zhixia , Wang Xiaoru , Fu Qi , Huang Huabin , Lin Lili , Huang Lixing , Qin Yingxue , Zhang Jiaonan , Yan Qingpi 

TITLE=The Effect of tonB Gene on the Virulence of Pseudomonas plecoglossicida and the Immune Response of Epinephelus coioides

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.720967

DOI=10.3389/fmicb.2021.720967

ISSN=1664-302X

ABSTRACT=<p><italic>Pseudomonas plecoglossicida</italic> is the causative agent of “visceral white spot disease” in cultured fish and has resulted in serious economic losses. <italic>tonB</italic> gene plays a crucial role in the uptake of nutrients from the outer membranes in Gram-negative bacteria. The previous results of our lab showed that the expression of <italic>tonB</italic> gene of <italic>P. plecoglossicida</italic> was significantly upregulated in the spleens of infected <italic>Epinephelus coioides</italic>. To explore the effect of <italic>tonB</italic> gene on the virulence of <italic>P. plecoglossicida</italic> and the immune response of <italic>E. coioides, tonB</italic> gene of <italic>P. plecoglossicida</italic> was knocked down by RNAi; and the differences between the wild-type strain and the <italic>tonB</italic>-RNAi strain of <italic>P. plecoglossicida</italic> were investigated. The results showed that all of the four mutants of <italic>P. plecoglossicida</italic> exhibited significant decreases in mRNA of <italic>tonB</italic> gene, and the best knockdown efficiency was 94.0%; the survival rate of <italic>E. coioides</italic> infected with the <italic>tonB</italic>-RNAi strain was 20% higher than of the counterpart infected with the wild strain of <italic>P. plecoglossicida</italic>. Meanwhile, the <italic>E. coioides</italic> infected with the <italic>tonB</italic>-RNAi strain of <italic>P. plecoglossicida</italic> carried less pathogens in the spleen and less white spots on the surface of the spleen; compared with the wild-type strain, the motility, chemotaxis, adhesion, and biofilm formation of the <italic>tonB</italic>-RNAi strain were significantly attenuated; the transcriptome data of <italic>E. coioides</italic> infected with the <italic>tonB</italic>-RNAi strain were different from the counterpart infected with the wild strain of <italic>P. plecoglossicida</italic>; the antigen processing and presentation pathway and the complement and coagulation cascade pathway were the most enriched immune pathways. The results indicated that <italic>tonB</italic> was a virulence gene of <italic>P. plecoglossicida</italic>; <italic>tonB</italic> gene was involved in the regulation of motility, chemotaxis, adhesion, and biofilm formation; <italic>tonB</italic> gene affected the immune response of <italic>E. coioides</italic> to <italic>P. plecoglossicida</italic> infection.</p>