H-NS binding to evpB and evpC and repressing T6SS expression in fish pathogen Edwardsiella piscicida

Abstract

Edwardsiella piscicida is an important causative agent of hemorrhagic septicemia in fish and infects both cultured and wild fish species. Type VI secretion system (T6SS) was proved to play important roles in pathogenesis of E. piscicida. In this study, it was demonstrated that the expression of T6SS genes evpB and evpC was under control of the global regulator H-NS in E. piscicida and the transcriptional level of evpB and evpC was significantly down-regulated by H-NS. Compared to the wild type, the transcriptional levels of evpB and evpC were up-regulated in hns null mutant, while down-regulated in hns overexpression strain. The results of EMSA and DNase I footprinting revealed that H-NS protein directly bound to upstream region of evpC at multiple sites. A high-affinity motif with a 9-nucleotide sequence 5'-ATATAAAAT-3' was defined for H-NS preferential recognition based on the feature of the binding sites. These results indicated that H-NS acted cooperatively to form extended nucleoprotein filaments on target DNA. Site-directed mutagenesis of H-NS further showed that R86 played an essential role in T6SS gene binding. These findings highlighted the mechanisms underlying the complex regulation network of T6SS by H-NS in E. piscicida.

The role of UhpA in regulating the virulence gene expression in Edwardsiella piscicida

“…Meanwhile, EsrA and EsrB are responsible for T3SS regulation in E. piscicida (Leung et al., 2019; Wang et al., 2010). Also, EvpB and EvpC proteins regulated iron‐restricted conditions in vitro had a crucial role in the T6SS‐mediated pathogenesis of E. piscicida (Cui et al., 2016). The results of this study show that the flagellar‐related gene, T3SS‐related gene and T6SS‐related gene expressions were higher than the ones in the wild strains.…”

“…The pathogenesis of E. piscicida includes many virulence factors such as the production of haemolysis (Buján et al., 2018; Wang et al., 2010), filament structural protein of flagellar (He et al., 2012), possession of type Ш secretion system (T3SS) (Leung et al., 2019; Wang et al., 2010) and type VI secretion system (T6SS) (Cui et al., 2016), production of growth metabolism (Hu et al., 2014; Marietou et al., 2018), and ability to adhere, invade, survive and replicate in host cells (Leung et al., 2019). Additionally, most of them were regulated by the two‐component signal transduction system (TCS), such as UhpA/UhpB‐UhpC, which enables the cell to acquire phosphorylated sugars from its environment that can be used as carbon or energy sources (Liu et al., 2020).…”

Thioredoxin H (TrxH) contributes to adversity adaptation and pathogenicity of Edwardsiella piscicida

“…Since E. piscicida is an important pathogen of aquatic animals, more and more studies about E. piscicida are reported. A large number of virulence factors/systems, such as type III (T3SS) and type VI (T6SS) secretion systems, a two-component regulatory system, hemolysin, LuxS/AI-2 quorum sensing system, molecular chaperons and RNA-binding protein Hfq, ferric uptake regulator, lysozyme inhibitors, and so on, are known to be involved in E. piscicida stress resistance or pathogenicity [9–13]. Accumulating evidence has made clear that E. piscicida is an intracellular pathogen with the capacity to evade host immune defense [11, 14].…”