DotU expression is highly induced during in vivo infection and responsible for virulence and Hcp1 secretion in avian pathogenic Escherichia coli.

Shaohui Wang,Shengqing Yu,Yichao Zhao,Xiangan Han,Yue Han,Qingmei Meng,Chan Ding,Jianjun Dai,Denghui Yang

doi:10.3389/fmicb.2014.00588

Abstract

Type VI secretion systems (T6SSs) contribute to pathogenicity in many pathogenic bacteria. Three distinguishable T6SS loci have been discovered in avian pathogenic Escherichia coli (APEC). The sequence of APEC T6SS2 locus is highly similar to the sequence of the newborn meningitis Escherichia coli (NMEC) RS218 T6SS locus, which might contribute to meningitis pathogenesis. However, little is known about the function of APEC T6SS2. We showed that the APEC T6SS2 component organelle trafficking protein (DotU) could elicit antibodies in infected ducks, suggesting that DotU might be involved in APEC pathogenicity. To investigate DotU in APEC pathogenesis, mutant and complemented strains were constructed and characterized. Inactivation of the APEC dotU gene attenuated virulence in ducks, diminished resistance to normal duck serum, and reduced survival in macrophage cells and ducks. Furthermore, deletion of the dotU gene abolished hemolysin-coregulated protein (Hcp) 1 secretion, leading to decreased interleukin (IL)-6 and IL-8 gene expression in HD-11 chicken macrophages. These functions were restored for the complementation strain. Our results demonstrated that DotU plays key roles in the APEC pathogenesis, Hcp1 secretion, and intracellular host response modulation.

Highlights

The protein secretion system is a common strategy for successful infection in hosts by Gram-negative bacteria (Saier, 2006)
Previous studies showed that avian pathogenic Escherichia coli (APEC) T6SS1 is involved in colonization and proliferation in systemic infections and T6SS2 is responsible for intramacrophage survival, cytokine and chemokine release, and host cell apoptosis
Our study showed that APEC dotU was expressed at low levels in LB culture

Summary

Introduction

The protein secretion system is a common strategy for successful infection in hosts by Gram-negative bacteria (Saier, 2006). The exact function of most T6SS proteins is not known, the majority are necessary for secretion of effector proteins including hemolysin-coregulated protein (Hcp), valine-glycine repeat protein (VgrG), ClpV, intracellular multiplication protein (IcmF) and organelle trafficking protein (DotU; Wu et al, 2008; Pukatzki et al, 2009). Hcp and VgrG are mutually dependent for secretion in V. cholerae, Edwardsiella tarda and enteroaggregative Escherichia coli (EAEC; Dudley et al, 2006; Pukatzki et al, 2007; Zheng and Leung, 2007), suggesting that Hcp and VgrG are secreted proteins and machine components. ClpV energizes secretion of effector proteins that form oligomeric complexes that enable ATP hydrolysis-dependent protein transport (Schlieker et al, 2005; Pukatzki et al, 2009).

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Conclusion