Biology subjects

Lagage, V.

Publications and source records attributed to Lagage, V..

4 recordsLinked to original sources

bioRxiv2025

Real-time visualisation of the intracellular dynamics of Shigella virulence plasmid

Bacterial plasmids play critical roles in horizontal gene transfer, antibiotic resistance, virulence, and in shaping the interaction of bacteria with their environment, including those encountered in their hosts. They are integral to bacterial evolution as they act as vectors for rapid genetic change and adaptation. Shigella sonnei is a human-adapted pathogen that is a leading cause of bacillary dysentery and a significant threat to public health. In common to all species of Shigella, S. sonnei harbours an [~] 210 kb virulence plasmid, pINV, which is essential for its virulence. pINV encodes a Type III secretion system that mediates bacterial invasion of epithelial cells. Understanding the dynamics of replication and segregation of pINV is therefore necessary to define how Shigella retains the plasmid and thence virulence. In this study, we used three fluorescent tagging approaches to detect the presence of pINV in live S. sonnei to allow tracking of the plasmid during cell division. Conclusively, we found that tagging the plasmid with the parS-ParB partitioning system sequences from Caulobacter crescentus chromosome, allowed suitable visualization of the single copy pINV in S. sonnei. This comprehensively enabled us to monitor the location and segregation of the plasmid during bacterial growth.

molecular biology↗

bioRxiv2022

Environmental feedback drives oxidative stress response heterogeneity in bacterial populations

Induction of phenotypic heterogeneity is a ubiquitous consequence of bacterial stress responses. It is commonly postulated that isogenic cells exploit stochastic molecular fluctuations to generate phenotypic heterogeneity as a population survival strategy (termed bet-hedging). However, it is also possible that each cell attempts to maximise its own chances of survival. In that case, the apparent heterogeneity could either be caused by inevitable molecular noise or by underlying deterministic mechanisms which have escaped observation. Here, we investigated the sources and consequences of gene expression heterogeneity in the response of Escherichia coli cells to hydrogen peroxide (H2O2) stress. A machine-learning model accurately predicted the variable responses of individual cells growing in structured populations, indicating that the phenotypic heterogeneity has a deterministic origin. The model further showed that spatio-temporal dynamics in H2O2 concentration were dictated by the H2O2 scavenging capacity and morphology of cells in the local environment. Hence, oxidative stress response fluctuations were in fact the result of a precise and rapid feedback between each cell and its immediate environment. Although single cells optimise their individual responses, the formation of short-range H2O2 gradients by their scavenging activities increases stress tolerance at the population level and leads to spatial variation in mutation rates.

microbiology↗

bioRxiv2022

Adaptation delay causes a burst of mutations in bacteria responding to oxidative stress

Understanding the interplay between phenotypic plasticity and genetic adaptation is a long-standing focus of evolutionary biology. In bacteria, the oxidative stress response limits the formation of mutagenic reactive oxygen species (ROS) under diverse stress conditions. This suggests that the dynamics of the oxidative stress response are closely tied to the timing of the mutation supply that fuels genetic adaptation to stress. Here, we explored how mutation rates change in real-time in Escherichia coli cells during continuous hydrogen peroxide treatment in microfluidic channels. By visualising nascent DNA replication errors, we uncovered that sudden oxidative stress causes a burst of mutations. We developed a range of single-molecule and single-cell microscopy assays to determine how these mutation dynamics arise from phenotypic adaptation mechanisms. Signalling of peroxide stress by the transcription factor OxyR rapidly induces ROS scavenging enzymes. However, an adaptation delay leaves cells vulnerable to the mutagenic and toxic effects of hydroxyl radicals generated by the Fenton reaction. Resulting DNA damage is counteracted by a spike in DNA repair activities during the adaptation delay. Prior stress exposure or constitutive OxyR induction allowed cells to avoid the burst of mutations. Similar observations for alkylation stress show that mutation bursts are a general phenomenon associated with adaptation delays.

microbiology↗

bioRxiv2020

Distinct activities of bacterial condensins for chromosome management in Pseudomonas aeruginosa.

Bacteria encompass three types of structurally related SMC complexes referred to as condensins. Smc-ScpAB is present in most bacteria while MukBEF is found in enterobacteria and MksBEF is scattered over the phylogenic tree. The contributions of these condensins to chromosome management were characterized in Pseudomonas aeruginosa that carries both Smc-ScpAB and MksBEF. In this bacterium, SMC-ScpAB controls chromosome disposition by juxtaposing chromosome arms. In contrast, MksBEF is critical for chromosome segregation in the absence of the main segregation system and affects the higher-order architecture of the chromosome by promoting DNA contacts in the megabase range. Strikingly, our results reveal a prevalence of Smc-ScpAB over MksBEF involving a coordination of their activities with the DNA replication process. They also show that E. coli MukBEF can substitute for MksBEF in P. aeruginosa while prevailing over Smc-ScpAB. Altogether, our results reveal a hierarchy between activities of bacterial condensins on the same chromosome.

microbiology↗