Biology subjects

Wimmi, S.

Publications and source records attributed to Wimmi, S..

4 recordsLinked to original sources

bioRxiv2026

Differential active adhesion and a capillary instability drive global eversion and dissemination of bacterial colonies

Attractive forces between cells determine the shape and sorting behaviour of bacterial colonies. During colony development, chemical gradients form within the colony but it is unclear how they affect cohesion. Here, we discover that such gradients trigger global eversion of proliferating colonies formed by the human pathogen Neisseria gonorrhoeae. Like a jet, the inner core flows towards the periphery where it is partially dispersed and partially spreads around the core of the colony. Living dispersed cells reform colonies leading to rapid dissemination. The eversion depends on local oxygen depletion, which reduces the activity of the molecular motors that govern self-attraction: before the eversion the colony consists of a weakly cohesive spherical core surrounded by a strongly cohesive shell. An idealized computational model reveals that in this configuration a non-linear instability occurs, akin to a capillary instability, when the thickness of the strongly interacting shell falls below a critical value. We show that the probability for eversion strongly depends on the motor-generated attractive force between bacteria. Overall, our results indicate that chemical gradients induce spontaneous symmetry breaking in a mechanically active colony, thereby triggering a non-linear shape instability. This instability generates large-scale cellular fluxes that redistribute bacteria toward environments more favourable for their growth.

biophysics↗

bioRxiv2023

A conserved cell-pole determinant organizes proper polar flagellum formation

The coordination of cell cycle progression and flagellar synthesis is a complex process in motile bacteria. In {gamma}-proteobacteria, the localization of the flagellum to the cell pole is mediated by the SRP-type GTPase FlhF. However, the mechanism of action of FlhF, and its relationship with the cell pole landmark protein HubP remain unclear. In this study, we discovered a novel protein called FipA that is required for normal FlhF activity and function in polar flagellar synthesis. We demonstrated that membrane-localized FipA interacts with FlhF and is required for normal flagellar synthesis in Vibrio parahaemolyticus, Pseudomonas putida, and Shewanella putrefaciens, and it does so independently of the polar localization mediated by HubP. FipA exhibits a dynamic localization pattern and is present at the designated pole before flagellar synthesis begins, suggesting its role in licensing flagellar formation. This discovery provides insight into a new pathway for regulating flagellum synthesis and coordinating cellular organization in bacteria that rely on polar flagellation and FlhF-dependent localization.

microbiology↗

bioRxiv2022

Pilotins are mobile T3SS components involved in assembly and substrate specificity of the bacterial type III secretion system

In animal pathogens, assembly of the type III secretion system injectisome requires the presence of so-called pilotins, small lipoproteins that assist the formation of the secretin ring in the outer membrane. Using a combination of functional assays, interaction studies, proteomics, and live-cell microscopy, we determined the contribution of the pilotin to the assembly, function, and substrate selectivity of the T3SS and identified potential new downstream roles of pilotin proteins. In absence of its pilotin SctG, Yersinia enterocolitica forms few, largely polar injectisome sorting platforms and needles. In line, most export apparatus subcomplexes are mobile in these strains, suggesting the absence of fully assembled injectisomes. Remarkably, while absence of the pilotin all but prevents export of early T3SS substrates, such as the needle subunits, it has little effect on secretion of late T3SS substrates, including the virulence effectors. We found that pilotins transiently interact with other injectisome components such as the secretin in the outer membrane, but mostly form transient mobile clusters in the bacterial membrane, which do not colocalize with assembled injectisomes. Together, these findings provide a new view on the role of pilotins during and after assembly of type III secretion injectisomes.

microbiology↗

bioRxiv2019

Dynamic relocalization of the cytosolic type III secretion system components ensures specific protein secretion

Many bacterial pathogens use a type III secretion system (T3SS) to manipulate host cells. Protein secretion by the T3SS injectisome is activated upon contact to any host cell, and it has been unclear how premature secretion is prevented during infection. We found that in gastrointestinal pathogens, cytosolic injectisome components are temporarily released from the proximal interface of the injectisome at low external pH, preventing protein secretion in acidic environments, such as the stomach. In Yersinia enterocolitica, low external pH is detected in the periplasm and leads to a partial dissociation of the inner membrane injectisome component SctD, which in turn causes the dissociation of the cytosolic T3SS components. This effect is reversed upon restoration of neutral pH, allowing a fast activation of the T3SS at the native target regions within the host. These findings indicate that the cytosolic components form an adaptive regulatory interface, which regulates T3SS activity in response to environmental conditions.

microbiology↗