Data Availability StatementThe transcriptome data have already been deposited to SRA data source under?the BioProject accession number PRJNA595449:?https://www. foods, soils, ocean water, and clean drinking water (Ghatak et al., 2016; Navarro\Garcia, Serapio\Palacios, Vidal, Salazar, & Tapia\Pastrana, 2014; Qin et al., 2014). It could trigger disease outbreaks in aquatic pets and result in high mortality (Qin, Lin, Chen, Xu, & Yan, 2016; da Silva et BNS-22 al., 2012). Furthermore, in 1970, this bacterium was reported to trigger individual infectious diarrhea (Helm & Stille, 1970), and it’s been described as one of the most common pathogens that cause severe public health problems (Igbinosa, Igumbor, Aghdasi, Tom, & Okoh, 2012). The pathogenicity and pathogenic mechanism of have also been reported (Gonzlez\Serrano, Santos, Garca\Lpez, & Otero, 2002; Li, 2011). Current study generally assumes the pathogenicity of is definitely closely related to the difficulty of its virulence factors, and moreover, different virulence factors cooperate with each other to jointly exert their pathogenic part (Shemesh, Tam, & Steinberg, 2007; Yu et al., 2005). However, the pathogenic mechanism of has not been fully explained to day, and the literature is actually contradictory (Chandrarathna et al., 2018; Vehicle der Marel, Schroers, Neuhaus, & Steinhagen, 2008). Our team have been tracking the bacterial diseases of farmed eel in Fujian China for about 20?years and isolated dozens of strains of (Gagan, Tanuja, & Aparna, 2012). Therefore, it regulates a variety of cellular functions PRKM10 including motility, biofilm formation, adaptation to acidic conditions, and toxicity (Bang, Audia, Park, & Foster, 2002; Bontemps\Gallo et al., 2019; Jubelin et al., 2005; Mattison, Oropeza, & Kenney, 2002; Silva et al., 2018). It has been demonstrated that OmpR regulates the flagellar pathway, the ability of bacteria to move, and the secretion of antibiotics in the bacteria (Park & Forst, 2006). In inactivation affects the manifestation of more than 100 genes, therefore causing changes in many bacterial physiological functions such as motility, biofilm formation, adaptability to acidic environments, and even pathogenicity (Kakuda et al., 2014). The latest researches exposed the two\component system EnvZ/OmpR could impact the pH and the virulence of and also impact the tolerance of bacteria to ethanol (Xi et al., 2019; Zhang, Ye, et al., 2018). Even though researches on EnvZ/OmpR have been extensive, you will find few reports within the function of this two\component system from your transcriptome level. And the function of EnvZ/OmpR in aquatic animal pathogen remains unfamiliar. Comparative transcriptomics can reveal the function of genes more fully from mRNA level, which help to deeply understand the function of genes. Since OmpR is the transcriptional regulatory BNS-22 element of the two\component system EnvZ/OmpR and takes on an important part in the pathogenicity of many bacteria, it is important to investigate the part it takes on in the pathogenesis of (Reboul et al., 2014), and in this study, the manifestation of was silenced in pathogenic B11 by RNAi technology. The phenotypes and transcriptome of crazy\type and silent strains were compared to explore the part of in the pathogenesisgrowth conditions: 37C, 220?rpm; B11 growth conditions: 28C, 220?rpm. The antibiotic chloramphenicol was added to the LB BNS-22 medium (pH?=?7.0) at a concentration of 34?g/ml. The strains and plasmids used in this study are listed in Table?A1. 2.2. Stable gene silence The expression of was stably silenced following previously described methods (Qin et al., 2014; Tokunaga et al., 2015; Zhang, Luo, et al., 2018; Zhang, Ye, et al., 2018; Zhang et al., 2019; Zhang, Yan, BNS-22 et al., 2018). The designed synthetic shRNA was annealed to form a double strand, which was then ligated to the pACYC184 plasmid after digestion with the enzymes by electroporation, and the stable\silencing strain in does not affect the growth of B11. (a) Expressions of in B11 strain and of three independent biological replicates. **on the virulence of B11 (Figure?2a) showed that can regulate the expression of multiple virulence genes, such as and positively regulates BNS-22 and and negatively regulates was inhibited, the LD50 of B11 decreased by an order of magnitude, which suggested that was likely involved in the regulation of bacterial virulence. Open in a separate window Figure 2 Effect of expression on the virulence of (red indicates significantly upregulated, and blue indicates significantly downregulated genes; the circle size indicates the amount of gene expression). (b) Expression of important virulence genes in from three independent biological replicates. **can regulate the expression of multiple chemotaxis and motility\related genes, thus regulating the chemotaxis of regulated and and negatively controlled and was inhibited favorably, the power for bacterial chemotaxis.