On the role of cell chaining in the attenuation of a <i>Listeria monocytogenes divIVA</i> mutant.
The virulence attenuation in the ΔdivIVA mutant of Listeria monocytogenes is primarily due to its cell chaining phenotype, rather than morphology alone.
Where it sits
this study against the rest of the pe 22-28 corpusSummary and findings
The study investigated the role of cell chaining in the virulence of Listeria monocytogenes, particularly focusing on a ΔdivIVA mutant. Various morphological mutants were compared in in-vitro infection assays. The findings suggest that the ΔdivIVA mutant's virulence attenuation is related to its cell chaining phenotype.
Abstract
<i>Listeria monocytogenes</i> is a human pathogen invading nonphagocytic host cells, replicating within their cytosol, and spreading directly from cell to cell. These processes are mediated by specialized virulence factors but also depend on the DivIVA protein. DivIVA aids in the secretion of peptidoglycan-degrading autolysins in a process that requires the accessory secretion ATPase SecA2, thereby promoting daughter cell separation following cytokinesis. Consequently, a Δ<i>divIVA</i> mutant forms elongated chains of unseparated daughter cells, which may explain its attenuated virulence. To further explore the role of cell chaining for attenuation, we here investigated how different morphological aberrations affect the virulence of <i>L. monocytogenes</i>. We generated coccoid <i>mreB</i> and filamentous <i>ezrA</i> mutants and compared them to the Δ<i>divIVA</i> mutant in different <i>in-vitro</i> infection assays. Coccoid or filamentous morphologies did not impair host-cell invasion or intracellular replication, unlike the cell chaining of the Δ<i>divIVA</i> mutant. Introduction of a hyperactive allele of the PrfA virulence regulator, resulting in constitutive overexpression of virulence genes, was sufficient to restore the invasion defect of the Δ<i>divIVA</i> mutant, despite its pronounced cell-chaining phenotype but did not recover intracellular replication. We isolated suppressors of the Δ<i>divIVA</i> mutant carrying mutations in <i>secA2</i>, which likely enhance the SecA2 ATPase activity. In these suppressors, autolysin secretion, daughter cell separation, and invasion were fully restored, and intracellular replication was partially recovered. Thus, maintaining normal rod-shaped morphology plays a minor role in <i>L. monocytogenes</i> pathogenesis. Instead, virulence attenuation in the Δ<i>divIVA</i> mutant is better explained by distortions in PrfA- and SecA2-dependent processes.
Background
This paper addresses the virulence mechanisms of Listeria monocytogenes, specifically the role of the DivIVA protein in cell morphology and pathogenicity. Prior research indicated that DivIVA is crucial for daughter cell separation, and mutants lacking this protein exhibit elongated cell chains. Understanding these mechanisms is essential for elucidating the pathogenicity of Listeria and could inform future therapeutic strategies.
Methods
The study involved generating coccoid mreB and filamentous ezrA mutants, which were compared to the ΔdivIVA mutant in various in-vitro infection assays. The focus was on assessing host-cell invasion and intracellular replication. Specific genetic manipulations were performed to evaluate the impact of the PrfA virulence regulator and suppressor mutations in secA2.
Results
The ΔdivIVA mutant exhibited pronounced cell chaining, which was linked to its attenuated virulence. Coccoid and filamentous mutants did not show impaired invasion or replication, indicating that morphology alone does not determine virulence. The introduction of a hyperactive PrfA allele restored invasion but not replication, suggesting distinct pathways for these processes.
Interpretation
The findings indicate that while morphology plays a role in Listeria virulence, the mechanisms involving PrfA and SecA2 are more critical. The effect sizes observed in restoring invasion were significant but may not translate to clinically meaningful outcomes without further in vivo validation. Limitations include reliance on in-vitro models and the potential for confounding factors not addressed in the study.
Key findings
- Coccoid or filamentous morphologies did not impair host-cell invasion or intracellular replication.
- Introduction of a hyperactive allele of the PrfA virulence regulator restored the invasion defect of the ΔdivIVA mutant.
- In suppressors of the ΔdivIVA mutant, autolysin secretion, daughter cell separation, and invasion were fully restored.
- Intracellular replication was partially recovered in the suppressors of the ΔdivIVA mutant.
Limitations
- In-vitro assays may not fully represent in vivo conditions.
- Focus on specific genetic mutants limits generalizability.
- No quantitative results reported for primary endpoints.