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J Bacteriol. 2019 Oct 21. pii: JB.00428-19. doi: 10.1128/JB.00428-19. [Epub ahead of print]

Decoupling filamentous phage uptake and energy of the TolQRA motor in Escherichia coli.

Author information

1
Laboratoire d'Ingénierie des Systèmes Macromoléculaires, UMR7255, Institut de Microbiologie de la Méditerranée, Aix-Marseille Univ - CNRS, 31 Chemin Joseph Aiguier, CS 70071, 13402 Marseille Cedex 09, France.
2
Laboratoire d'Ingénierie des Systèmes Macromoléculaires, UMR7255, Institut de Microbiologie de la Méditerranée, Aix-Marseille Univ - CNRS, 31 Chemin Joseph Aiguier, CS 70071, 13402 Marseille Cedex 09, France. lhouot@imm.cnrs.fr.

Abstract

Filamentous phages are non-lytic viruses that specifically infect bacteria, establishing a persistent association with their host. The phage particle has no machinery for generating energy and parasitizes its host existing structures in order to cross the bacterial envelope and deliver its genetic material. The import of filamentous phages across the bacterial periplasmic space requires some of the components of a macro-complex of the envelope known as the Tol system. This complex uses the energy provided by the proton-motive force of the inner membrane to perform essential and highly energy-consuming functions of the cell, such as envelope integrity maintenance and cell division. It has been suggested that phages take advantage of pmf-driven conformational changes in the Tol system to transit across the periplasm. However, this hypothesis has not been formally tested. In order to decouple the role of the Tol system in cell physiology and during phage parasitism, we used mutations on conserved essential residues known for inactivating pmf-dependent functions of the Tol system. We identified impaired Tol complexes that remain fully efficient for filamentous phage uptake. We further demonstrate that the TolQ-TolR homologous motor, ExbB-ExbD, normally operating with the TonB protein, is able to promote phage infection along with full length TolA.IMPORTANCEFilamentous phages are widely distributed symbionts of gram-negative bacteria, some of them being linked to genome evolution and virulence of their host. However, the precise mechanism that permit their uptake across the cell envelope is poorly understood. The canonical phage model Fd requires the TolQRA protein complex in the host envelope, which is suspected to translocate proton across the inner membrane. In this study, we show that phage uptake proceeds in the presence of assembled but non-functional TolQRA complex. Moreover, our results unravel an alternative route for phage import that relies on the ExbB-ExbD proteins. This work provides new insights into the fundamental mechanisms of phage infection, and might be generalized to other filamentous phages responsible for pathogen emergence.

PMID:
31636109
DOI:
10.1128/JB.00428-19

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