Biology subjects

Wielert, I.

Publications and source records attributed to Wielert, I..

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↗

bioRxiv2025

Gonococcal aggregation causes upregulation of genes involved in antibiotic tolerance

Aggregation and biofilm formation can increase the tolerance of bacteria to external stressors, including antibiotic treatment. While resistant bacteria grow at an elevated drug dose, tolerant bacteria survive longer-term treatment. The mechanisms by which aggregation confers tolerance are insufficiently characterized for most organisms, including the human pathogen Neisseria gonorrhoeae. We hypothesize that bacterial aggregation causes upregulation of genes involved in tolerance and that deletion of these genes increases killing rates during antibiotic treatment. To test this hypothesis and identify genes involved in gonococcal tolerance, we compared the transcriptome of aggregating and planktonic N. gonorrhoeae strains. In general, the transcriptome analysis shows that aggregation causes a strong upregulation of prophage-related genes and a shift towards anaerobic respiration. We generated deletion strains for the twenty most upregulated genes and measured their killing kinetics during treatment with the clinically relevant antibiotics ceftriaxone or ciprofloxacin. We identified five genes and one multigene segment that are involved in gonococcal antibiotic tolerance. These include prophage genes whose deletion affects tolerance differently in aggregating and planktonic strains. Furthermore, deletion of genes encoding a putative multi-drug efflux pump, an alcohol dehydrogenase, and a DNA repair protein reduces tolerance. In summary, we have identified multiple genes that affect antibiotic tolerance and are upregulated in response to aggregation. Author summaryOften bacterial infections recur after antibiotic treatment because not all of the bacteria were killed. The ability to survive treatment by bactericidal drugs is termed tolerance. It is well established that aggregation can increase tolerance by reducing growth and metabolism. However, the genes involved in tolerance are not well characterized, especially in the human pathogen Neisseria gonorrhoeae. Here, we aim to identify such genes by following the hypothesis that aggregation upregulates genes that cross-protect N. gonorrhoeae from antibiotic treatment. We show that prophage-associated genes are strongly upregulated in aggregates and that deletion of various phage genes affects tolerance to the currently administered drug, ceftriaxone. We identify three additional genes belonging to different functional classes whose deletion reduces tolerance to ciprofloxacin. Our study is an important step towards understanding the molecular mechanisms of gonococcal antibiotic tolerance. In particular, we propose that prophages could serve as a target for the treatment of tolerant gonococcal infections.

microbiology↗

bioRxiv2023

Antigenic variation impacts gonococcal lifestyle and antibiotic tolerance by modulating interbacterial forces

Type 4 pili (T4P) are multifunctional filaments involved in adhesion, surface motility, colony formation, and horizontal gene transfer. These extracellular polymers are surface-exposed and, therefore, act as antigens. The human pathogen Neisseria gonorrhoeae uses pilin antigenic variation to escape immune surveillance, yet it is unclear how antigenic variation impacts other functions of T4P. Here, we addressed this question by replacing the major pilin of a laboratory strain of N. gonorrhoeae with pilins from clinical isolates. Structural predictions reveal filament features that vary from one strain to the next, with the potential to impact pilus:pilus interactions. Using a combination of laser tweezers, electron microscopy, and advanced image analysis, we explore the phenotypic consequences of these structural changes. We reveal that strains differing only in their major pilin sequence vary substantially in their attractive forces, which we attribute to variations in the stereochemistry of the T4P filament. In liquid culture, strongly interacting bacteria form colonies while weakly interacting bacteria retain a planktonic lifestyle. We show that lifestyle strongly affects growth kinetics and antibiotic tolerance. In the absence of external stresses, planktonic bacteria grow faster than colony-forming bacteria. In the presence of the antibiotics ceftriaxone and ciprofloxacin, the killing kinetics indicate strongly increased tolerance of colony-forming strains. We propose that pilin antigenic variation produces a mixed population containing variants optimized for growth, colonization, or survivability under external stress. Different environments select different variants, ensuring the survival and reproduction of the population as a whole. Significance statementNeisseria are highly successful human pathogens that continuously vary their surface structures to escape immune surveillance. Antigenic variation of the major pilin subunit causes variations of the structure of the Type 4 pilus, a surface exposed virulence factor. Here, we investigate the effect of pilin antigenic variation on bacterial lifestyle and tolerance against antibiotics. We find that pilin antigenic variation causes changes in the physical interactions between the bacteria, resulting in distinct aggregating and planktonic phenotypes. During treatment with antibiotics, aggregating strains are more tolerant than planktonic strains by an order of magnitude. Since tolerance tends to facilitate resistance development, pilin antigenic variation reduces the efficiency of antibiotic treatment.

microbiology↗

bioRxiv2020

Antibiotics modulate attractive interactions in bacterial colonies affecting survivability under combined treatment

Biofilm formation protects bacteria from antibiotics. Very little is known about the response of biofilm-dwelling bacteria to antibiotics at the single cell level. Here, we developed a cell-tracking approach to investigate how antibiotics affect structure and dynamics of colonies formed by the human pathogen Neisseria gonorrhoeae. Antibiotics targeting different cellular functions enlarge the cell volumes and modulate within-colony motility. Focusing on azithromycin and ceftriaxone, we identify changes in type 4 pilus (T4P) mediated cell-to-cell attraction as the molecular mechanism for different effects on motility. By using strongly attractive mutant strains, we reveal that the survivability under ceftriaxone treatment depends on motility. Combining our results, we find that sequential treatment with azithromycin and ceftriaxone is synergistic. Taken together, we demonstrate that antibiotics modulate T4P-mediated attractions and hence cell motility and colony fluidity. Author SummaryAggregation into colonies and biofilms can enhance bacterial survivability under antibiotic treatment. Aggregation requires modulation of attractive forces between neighboring bacteria, yet the link between attraction and survivability is poorly characterized. Here, we quantify these attractive interactions and show that different antibiotics enhance or inhibit them. Live-cell tracking of single cells in spherical colonies enables us to correlate attractive interactions with single cell motility and colony fluidity. Even moderate changes in cell-to-cell attraction caused by antibiotics strongly impact on within-colony motility. Vice versa, we reveal that motility correlates with survivability under antibiotic treatment. In summary, we demonstrate a link between cellular attraction, colony fluidity, and survivability with the potential to optimize the treatment strategy of commonly used drug combinations.

microbiology↗