A novel mechanism for the biogenesis of outer membrane vesicles in Gram-negative bacteria.

Sandro Roier,Ruth Prassl,Günther Daum,Franz G Zingl,Thomas O Eichmann,Katharina Weinzerl,Stefan Schild,Joachim Reidl,Bernhard Gadermaier,Lisa Klug,Mario F Feldman,Sanel Durakovic,Achim Lass,Paul Kohl,Fatih Cakar

doi:10.1038/ncomms10515

Abstract

Bacterial outer membrane vesicles (OMVs) have important biological roles in pathogenesis and intercellular interactions, but a general mechanism of OMV formation is lacking. Here we show that the VacJ/Yrb ABC (ATP-binding cassette) transport system, a proposed phospholipid transporter, is involved in OMV formation. Deletion or repression of VacJ/Yrb increases OMV production in two distantly related Gram-negative bacteria, Haemophilus influenzae and Vibrio cholerae. Lipidome analyses demonstrate that OMVs from VacJ/Yrb-defective mutants in H. influenzae are enriched in phospholipids and certain fatty acids. Furthermore, we demonstrate that OMV production and regulation of the VacJ/Yrb ABC transport system respond to iron starvation. Our results suggest a new general mechanism of OMV biogenesis based on phospholipid accumulation in the outer leaflet of the outer membrane. This mechanism is highly conserved among Gram-negative bacteria, provides a means for regulation, can account for OMV formation under all growth conditions, and might have important pathophysiological roles in vivo.

Highlights

Bacterial outer membrane vesicles (OMVs) have important biological roles in pathogenesis and intercellular interactions, but a general mechanism of OMV formation is lacking
Since this system is proposed to function as a PL transporter in maintaining the lipid asymmetry in the OM24, we performed lipidome analyses to demonstrate that OMVs from PL transporter mutants in H. influenzae are enriched in PLs, which are likely to be incorporated into the outer leaflet of the vesicle membrane
We report that iron limitation leads to a ferric uptake regulator (Fur)-dependent downregulation of the VacJ/Yrb ABC transport system correlating with an increased OMV production in H. influenzae, V. cholerae and E. coli

Summary

Introduction

Bacterial outer membrane vesicles (OMVs) have important biological roles in pathogenesis and intercellular interactions, but a general mechanism of OMV formation is lacking. Our results suggest a new general mechanism of OMV biogenesis based on phospholipid accumulation in the outer leaflet of the outer membrane This mechanism is highly conserved among Gram-negative bacteria, provides a means for regulation, can account for OMV formation under all growth conditions, and might have important pathophysiological roles in vivo. All these proposed models of OMV formation require either genetic manipulations, the presence of stress, or are far only applicable to a single bacterial species It is currently unknown whether Gram-negative bacteria share a conserved general mechanism of OMV biogenesis that is amenable to regulation. We propose a novel and potentially highly conserved bacterial OMV biogenesis mechanism, which provides the opportunity of regulation and may represent a first general mechanism applicable to all Gram-negative bacteria

Methods

Results

Conclusion