Biology subjects

Ermoli, F.

Publications and source records attributed to Ermoli, F..

3 recordsLinked to original sources

bioRxiv2025

Activation of the Yersinia type III secretion system induces large-scale chromosomal and virulence plasmid DNA rearrangements

The type III secretion system (T3SS) is used by Gram-negative bacteria, including important pathogens, to manipulate eukaryotic target cells by injecting effector proteins. Type III secretion and bacterial physiology are known to be tightly interconnected and influence each other. Most notably, secreting cells undergo growth arrest in the T3SS model organisms Yersinia, Salmonella and Shigella. The molecular basis of this phenotype, referred to as secretion-associated growth inhibition, is debated. In Yersinia, T3SS genes are encoded extra-chromosomally in the plasmid of Yersinia virulence (pYV), whose copy number increases upon induction of T3SS secretion. In this study, we characterize the link between T3SS activity and subcellular organization by localizing and quantifying the pYV and chromosomal DNA in Yersinia enterocolitica. We find that activation of secretion not only increases the number of pYV plasmids per bacterium, but that the plasmids also move towards the membrane and poles. This relocalization is not caused by transertion (coupled transcription, translation and translocation) of effectors, but part of a broader DNA rearrangement, leading to a distinct relocalization of chromosomal DNA to mid-cell. We hypothesize that these striking DNA rearrangements occurring during secretion are a main factor in the secretion-associated growth inhibition of pathogenic bacteria.

microbiology↗

bioRxiv2024

Yersinia actively downregulates type III secretion and adhesion at higher cell densities

The T3SS injectisome is used by Gram-negative bacteria, including important pathogens, to manipulate eukaryotic target cells by injecting effector proteins. While in some bacterial species, T3SS-negative bacteria benefit from the activity of their T3SS-positive siblings, the T3SS model organism Yersinia enterocolitica was thought to uniformly express and assemble injectisomes. In this study, we found that Yersinia actively suppress T3SS expression, assembly and activity at higher cell densities, such as inside microcolonies. This effect is highly specific to the T3SS, reversible, and distinct from stationary phase adaptation. It is conferred by the main T3SS transcription factor VirF, which is downregulated at higher densities and whose in trans expression restores T3SS activity. Transcript analysis showed that this effect is mediated by increased levels of the regulatory RNAs CsrBC, which sequester the regulatory protein CsrA and destabilize the virF transcript. The concomitant downregulation of the VirF-dependent adhesin YadA led to a drastic reduction in bacterial cell adhesion. We propose that this active suppression of T3SS secretion and cell attachment at higher local bacterial densities promotes a switch during Yersinia infection from a T3SS-active colonization stage to a bacterial replication and dissemination phase.

microbiology↗

bioRxiv2021

SwrA as global modulator of the two-component system DegS/U in B. subtilis

The two-component system DegS/U of Bacillus subtilis controls more than one hundred genes involved in several different cellular behaviours. Since the consensus sequence recognized by the response regulator DegU has not been clearly defined yet, mutations in either component have been crucial in the identification of the cellular targets of this regulatory system. Over the years, the degU32Hy mutant allele, that was supposed to mimic the activated regulator, has been commonly used to define the impact of this TCS on its regulated genes in domestic strains. SwrA encodes a small protein essential for swarming motility and for poly-{gamma}-glutamate biosynthesis and is only present in wild strains. Previous work indicated that SwrA is partnering with DegU~P in exerting its role on both phenotypes. In this work, inserting a degS200Hy mutation in swrA+ and swrA- isogenic strains we demonstrate that SwrA modulates the action of DegU~P on two new phenotypes, subtilisin expression and competence for DNA uptake, with a remarkable effect on transformation. These effects cannot not be appreciated with the DegU32Hy mutant as it does not mirror the wild-type DegU protein in its ability to interact with SwrA.

genetics↗