Enterohaemorrhagic Escherichia coli activates nitrate respiration to benefit from the inflammatory response for initiation of microcolony-formation

Risa Nada,Toru Tobe,Hilo Yen,Shinya Ebihara

doi:10.1186/s12866-020-01946-w

Risa Nada, Toru Tobe + Show 2 more

Open Access

https://doi.org/10.1186/s12866-020-01946-w

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Journal: BMC microbiology	Publication Date: Aug 20, 2020
Citations: 2	License type: open-access

Affiliation: Osaka University

Abstract

BackgroundFor successful colonization, enterohaemorrhagic Escherichia coli (EHEC) injects virulence factors, called effectors, into target cells through the type three secretion system (T3SS), which is composed of a needle and basal body. Under anaerobic conditions, the T3SS machinery remains immature and does not have a needle structure. However, activation of nitrate respiration enhances the completion of the T3SS machinery. Because nitric oxide released by the host inflammatory response increases nitrate concentration, we sought to determine the effect of the inflammatory response on initiation of EHEC microcolony-formation.ResultsThe colony-forming capacity was increased in accordance with the increase of nitrate in the medium. The addition of the nitric oxide-producing agent NOR-4 also enhanced the adherence capacity, which was dependent on nitrate reductase encoded by the narGHJI genes. Culture supernatant of epithelial cells, which was stimulated by a cytokine mixture, enhanced the colony-forming capacity of wild-type EHEC but not of the narGHJI mutant. Finally, colony formation by wild-type EHEC on epithelial cells, which were preincubated with heat-killed bacteria, was higher than the narGHJI mutant, and this effect was abolished by aminoguanidine hydrochloride, which is an iNOS (inducible nitric oxide synthase) inhibitor.ConclusionsThese results indicate that the inflammatory response enhances EHEC adherence by increasing nitrate concentration.

Highlights

For successful colonization, enterohaemorrhagic Escherichia coli (EHEC) injects virulence factors, called effectors, into target cells through the type three secretion system (T3SS), which is composed of a needle and basal body
Enhancement of type 3 secretion system (T3SS) activity by nitrate In our previous study, maturation of the T3SS machinery under anaerobic conditions was achieved by the activation of specific anaerobic respiration using an electron acceptor as nitrate
To show the dependency of T3SS function and adherence capacity on nitrate, an EHEC wild-type strain was grown in LB medium containing various concentrations of nitrate under microanaerobic conditions at 37 °C

Summary

Introduction

Enterohaemorrhagic Escherichia coli (EHEC) injects virulence factors, called effectors, into target cells through the type three secretion system (T3SS), which is composed of a needle and basal body. The needle-like structure protrudes from the surface of the membrane [8]. The needle of the T3SS machinery of EHEC and enteropathogenic E. coli (EPEC) is covered by a sheath-like structure composed of EspA. The T3SS machinery of EHEC stays in an immature complex, which lacks the needle structure. Activation of specific anaerobic respiration, such as nitrate and TMAO respirations, triggers maturation by producing a needle on the T3SS machinery without increase of expression of T3S components [9]

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