Outer Membrane Vesicles Derived from Klebsiella pneumoniae Are a Driving Force for Horizontal Gene Transfer.

Federica Dell’Annunziata,Giovanni Boccia,Carmela Dell’Aversana,Nunzianna Doti,Veronica Folliero,Viviana Izzo,Anna De Filippis,Gianluigi Franci,Lucia Altucci,Fabrizio Dal Piaz,Giuliana Donadio,Marilena Galdiero,Massimiliano Galdiero

doi:10.3390/ijms22168732

Abstract

Gram-negative bacteria release Outer Membrane Vesicles (OMVs) into the extracellular environment. Recent studies recognized these vesicles as vectors to horizontal gene transfer; however, the parameters that mediate OMVs transfer within bacterial communities remain unclear. The present study highlights for the first time the transfer of plasmids containing resistance genes via OMVs derived from Klebsiella pneumoniae (K. pneumoniae). This mechanism confers DNA protection, it is plasmid copy number dependent with a ratio of 3.6 times among high copy number plasmid (pGR) versus low copy number plasmid (PRM), and the transformation efficiency was 3.6 times greater. Therefore, the DNA amount in the vesicular lumen and the efficacy of horizontal gene transfer was strictly dependent on the identity of the plasmid. Moreover, the role of K. pneumoniae-OMVs in interspecies transfer was described. The transfer ability was not related to the phylogenetic characteristics between the donor and the recipient species. K. pneumoniae-OMVs transferred plasmid to Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa and Burkholderia cepacia. These findings address the pivotal role of K. pneumoniae-OMVs as vectors for antimicrobial resistance genes spread, contributing to the development of antibiotic resistance in the microbial communities.

Highlights

Horizontal gene transfer (HGT) represents the main source of genetic material transfer among microorganisms [1]
To purify the Outer Membrane Vesicles (OMVs) derived from K. pneumoniae-pGR and K. pneumoniae-PRM, bacteria were grown in Luria-Bertani agar (LB) supplemented with ampicillin up to the late logarithmic-phase of the bacterial growth curve
Dynamic light scattering (DLS) analysis showed that OMVs derived from K. pneumoniae-pGR measured a size of 113.8 ± 53.7 nm and were characterized by a slightly heterogeneous size distribution, represented by the polydispersity index (PDI) of 0.223 (Figure 1C)

Summary

Introduction

Horizontal gene transfer (HGT) represents the main source of genetic material transfer among microorganisms [1]. Current knowledge of HGT is based on three widely described mechanisms for the exchange of genetic material between bacteria: transformation, conjugation and transduction [5,6,7]. Transformation involves the natural uptake of naked DNA from an extracellular environment; this phenomenon occurs when cells are in a physiological state of competence, regulated by 20–50 proteins [8,9]. Conjugation is a DNA transfer mechanism through the sexual pilus and requires cell-to-cell contact [10]. Conjugative systems are frequently associated with plasmid transfer [11]. Transduction entails the transfer of DNA between bacteria through the bacteriophage infections [12]. Several studies reported that HGT processes are facilitated by Outer Membrane Vesicles (OMVs) [14,15,16,17]

Methods

Results

Conclusion