ABSTRACT
Bacteria utilize complex type IV secretion systems (T4SSs) to translocate diverse effector proteins or DNA into target cells. Despite the importance of T4SSs in bacterial pathogenesis, the mechanism by which these translocation machineries deliver cargo across the bacterial envelope remains poorly understood, and very few studies have investigated the use of synthetic molecules to disrupt T4SS-mediated transport. Here, we describe two synthetic small molecules (C10 and KSK85) that disrupt T4SS-dependent processes in multiple bacterial pathogens.
Helicobacter pylori
exploits a pilus appendage associated with the
cag
T4SS to inject an oncogenic effector protein (CagA) and peptidoglycan into gastric epithelial cells. In
H. pylori
, KSK85 impedes biogenesis of the pilus appendage associated with the
cag
T4SS, while C10 disrupts
cag
T4SS activity without perturbing pilus assembly. In addition to the effects in
H. pylori
, we demonstrate that these compounds disrupt interbacterial DNA transfer by conjugative T4SSs in
Escherichia coli
and impede
vir
T4SS-mediated DNA delivery by
Agrobacterium tumefaciens
in a plant model of infection. Of note, C10 effectively disarmed dissemination of a derepressed IncF plasmid into a recipient bacterial population, thus demonstrating the potential of these compounds in mitigating the spread of antibiotic resistance determinants driven by conjugation. To our knowledge, this study is the first report of synthetic small molecules that impair delivery of both effector protein and DNA cargos by diverse T4SSs.
IMPORTANCE
Many human and plant pathogens utilize complex nanomachines called type IV secretion systems (T4SSs) to transport proteins and DNA to target cells. In addition to delivery of harmful effector proteins into target cells, T4SSs can disseminate genetic determinants that confer antibiotic resistance among bacterial populations. In this study, we sought to identify compounds that disrupt T4SS-mediated processes. Using the human gastric pathogen
H. pylori
as a model system, we identified and characterized two small molecules that prevent transfer of an oncogenic effector protein to host cells. We discovered that these small molecules also prevented the spread of antibiotic resistance plasmids in
E. coli
populations and diminished the transfer of tumor-inducing DNA from the plant pathogen
A. tumefaciens
to target cells. Thus, these compounds are versatile molecular tools that can be used to study and disarm these important bacterial machines.
Exploitation of Eukaryotic Ubiquitin Signaling Pathways by Effectors Translocated by Bacterial Type III and Type IV Secretion Systems