Biology subjects

Söderström, B.

Publications and source records attributed to Söderström, B..

7 recordsLinked to original sources

bioRxiv2025

Invasion and intracellular proliferation dynamics of non-pathogenic E. coli in model infection systems

Uropathogens are typically distinguished from commensal or laboratory E. coli strains by defined pathogenic behaviours. In this study, we compared the behaviour of non-pathogenic Escherichia coli to that of uropathogenic E. coli in diverse infection models at a single-cell level using live-cell fluorescence microscopy. Using in vitro microfluidics and ex vivo mouse urinary tract infection model systems, we demonstrated that the standard laboratory E. coli strain MG1655 can behave like a pathogen, invading and proliferating inside human and mouse urothelial cells. Upon exposure to stress by the addition of urine, we observed that MG1655 undergoes infection-related filamentation, and then subsequent reversal back to rod shape when the stress is removed. This observation supports that infection-related filamentation should be regarded as a stress response rather than a virulence factor. Taken together, our results show that under infection-favourable circumstances, even a well-studied non-pathogenic laboratory E. coli strain can exhibit what are considered pathogenic traits.

microbiology↗

bioRxiv2024

E. coli division machinery drives cocci development inside host cells

Escherichia coli is arguably one of the most studied bacterial model systems in modern biology. Under normal laboratory conditions E. coli adopts its characteristic rod-shape. However, during stress conditions E. coli has been shown to undergo conditional morphology changes to inhibit division and grow into highly elongated forms. Here, on the other end of the morphology spectra, using an in-vitro infection model system combined with advanced imaging we show uropathogenic E. coli rods dividing to form and proliferate as cocci inside human bladder epithelial cells. In these intracellular bacterial communities, the frequency of cell division outpaced the rate of cell growth, resulting in smaller cocci cells. This mechanism was guided by an active FtsZ-governed division machinery, directed to midcell by division-site placement systems. These results show how a previously uncharacterised level of morphological plasticity occurs in bacteria with traditionally well-defined rod shape.

microbiology↗

bioRxiv2023

Genetic requirements for uropathogenic E. coli proliferation in the bladder cell infection cycle

Uropathogenic Escherichia coli (UPEC) requires an adaptable physiology to survive the wide range of environments experienced in the host, including gut and urinary tract surfaces. To identify UPEC genes required during intracellular infection, we developed a transposon-directed insertion-site sequencing (TraDIS) approach for cellular infection models and searched for genes in a library of [~]20,000 E. coli UTI89 transposon-insertion mutants that are specifically required for growth in M9-glycerol minimal medium, and at the distinct stages of infection of cultured bladder epithelial cells. Some of the functional requirements apparent for growth in M9-glycerol overlapped with those for the intracellular stage of infection, notably nutrient utilization, polysaccharide and macromolecule precursor biosynthesis, and cell envelope stress tolerance. Two genes implicated in both conditions were confirmed through independent gene deletion studies: neuC (sialic acid capsule biosynthesis) and hisF (histidine biosynthesis). Distinct sets of UPEC genes were also implicated in bacterial dispersal, where UPEC erupt from bladder cells in highly filamentous or motile forms upon exposure to human urine, and during recovery from infection in rich (LB) medium. Genes linked to septal peptidoglycan processes, ytfB and dedD, appeared to play roles in dispersal and may help stabilize cell division or the envelope during envelope stress created during infection. Our findings support a view that the host intracellular environment and infection cycle are multi-nutrient limited and create stress that demand an array of biosynthetic, cell envelope integrity and biofilm-related functions of UPEC. IMPORTANCEUrinary tract infections (UTIs) are one of the most frequent infections worldwide. Uropathogenic Escherichia coli (UPEC), which accounts for [~]80 % of UTIs, must rapidly adapt to highly variable host environments, such as the gut, bladder sub-surface and urine. In this study, we searched for UPEC genes required for bacterial growth and survival throughout the cellular infection cycle. Genes required for de novo synthesis of biomolecules and cell envelope integrity appeared to be important, and other genes were also implicated in bacterial dispersal and recovery from infection of cultured bladder cells. With further studies of individual gene function, their potential as therapeutic targets may be realized. This study expands knowledge of the UTI infection cycle and establishes an approach to genome-wide functional analyses of stage-resolved microbial infections.

microbiology↗

bioRxiv2023

Application of nanotags and nanobodies for live cell single-molecule imaging of the Z-ring in Escherichia coli

Understanding where proteins are localized in a bacterial cell is essential for understanding their function and regulation. This is particularly important for proteins that are involved in cell division, which localize at the division septum and assemble into highly regulated complexes. Current knowledge of these complexes has been greatly facilitated by super-resolution imaging using fluorescent protein fusions. Herein we demonstrate with FtsZ that single-molecule PALM images can be obtained in-vivo using a genetically fused nanotag (ALFA) and a corresponding nanobody fused to mEos3.2. The methodology presented is applicable to other bacterial proteins.

microbiology↗

bioRxiv2023

Direct visualization of bacterial multispecies infection and symbiotic interactions within human bladder epithelial cells

Urinary tract infections (UTI) are one of the most common bacterial infections worldwide. While the overall infection course is known on a macroscale, bacterial behavior is not fully understood at the cellular level and bacterial pathophysiology during multispecies infection is not well characterized. Here we establish co-infection models combined with high resolution imaging to compare single- and multi-species bladder cell invasion events in three common uropathogens: uropathogenic Escherichia coli (UPEC), Klebsiella pneumoniae and Enterococcus faecalis. While all three species invaded the bladder cells, under flow conditions the Gram-positive E. faecalis was significantly less invasive compared to the Gram-negative UPEC and K. pneumoniae. When introduced simultaneously during an infection experiment, all three bacterial species sometimes invaded the same bladder cell, at differing frequencies suggesting complex interactions between bacterial species and bladder cells. Inside host cells, we observed encasement of E. faecalis colonies specifically by UPEC. During subsequent dispersal from the host cells, only the Gram-negative bacteria underwent infection-related filamentation (IRF). Taken together, our data suggest that bacterial multispecies invasions of single bladder cells are frequent and support earlier studies showing intraspecies cooperation on a biochemical level during UTI.

microbiology↗

bioRxiv2022

The role of bacterial size, shape and surface in macrophage engulfment of uropathogenic E. coli cells

Uropathogenic Escherichia coli (UPEC) can undergo extensive filamentation in the host during acute urinary tract infections (UTIs). It has been hypothesised that this morphological plasticity allows bacteria to avoid host immune responses such as macrophage engulfment. However, it is still unclear what properties of filaments are important in macrophage-bacteria interactions. The aim of this work was to investigate the contribution of bacterial biophysical parameters, such as cell size and shape, and physiological parameters, such as cell surface and the environment, to macrophage engulfment efficiency. Viable, reversible filaments of known lengths and volumes were produced in the UPEC strain UTI89 using a variety of methods, including exposure to cell-wall targeting antibiotics, genetic manipulation and isolation from an in vitro human bladder cell model. Quantification of the engulfment ability of macrophages using gentamicin-protection assays and fluorescence microscopy demonstrated that the ability of filaments to avoid macrophage engulfment is dependent on a combination of size (length and volume), shape, surface and external environmental factors. UTI89 filamentation was also found to occur independently of the SOS-inducible filamentation genes, sulA and ymfM, demonstrating the non-essential requirement of these genes for UTI89 filamentation and their ability to avoid macrophage engulfment. With several strains of UPEC now resistant to current antibiotics, our work identifies the importance of bacterial morphology during infection and may provide new ways to prevent or treat these infections via immune modulation or antimicrobials. Author SummaryUrinary tract infections (UTIs) are one of the most common bacterial infections worldwide with 50% of women suffering from a UTI during their lifetime. Escherichia coli is the primary bacteria responsible for UTIs and is usually found in short rod forms. However, during UTIs E. coli can elongate into extremely long thin shapes called filaments. Filaments are thought to be advantageous during infections because they are too long to be engulfed and killed by immune cells called macrophages. Due to increasing antibiotic resistance in bacteria there is a strong need for the discovery of new ways to treat infections and this is only possible once we thoroughly understand the mechanisms bacteria employ to overcome our immune response. Therefore, we investigated the effect of E. coli filamentation on macrophage engulfment along with other aspects of bacteria reported to influence engulfment. We found that the ability of filaments to avoid macrophage engulfment is dependent on a combination of size (length and volume), shape, surface and external environmental factors. Our research has highlighted the importance of bacterial shape changes during infections and provided a foundational understanding of macrophage engulfment of filaments. Eventually, this knowledge may reveal new targets for treatment of infections.

microbiology↗

bioRxiv2018

The bacterial DNA binding protein MatP involved in linking the nucleoid terminal domain to the divisome at midcell interacts with lipid membranes

Division ring formation at midcell is controlled by various mechanisms in Escherichia coli, one of them being the linkage between the chromosomal Ter macrodomain and the Z-ring mediated by MatP, a DNA binding protein that organizes this macrodomain and contributes to the prevention of premature chromosome segregation. Here we show that, during cell division, just before splitting the daughter cells, MatP seems to localize close to the cytoplasmic membrane, suggesting that this protein might interact with lipids. To test this hypothesis, we investigated MatP interaction with lipids in vitro. We found that MatP, when encapsulated inside microdroplets generated by microfluidics and giant vesicles, accumulates at phospholipid bilayers and monolayers matching the lipid composition in the E. coli inner membrane. MatP binding to lipids was independently confirmed using lipid coated microbeads and bio-layer interferometry assays. Interaction of MatP with the lipid membranes also occurs in the presence of the DNA sequences specifically targeted by the protein but there is no evidence of ternary membrane/protein/DNA complexes. We propose that the interaction of MatP with lipids may modulate its spatiotemporal localization and its recognition of other ligands.\n\nIMPORTANCEThe division of an E. coli cell into two daughter cells with equal genomic information and similar size requires duplication and segregation of the chromosome and subsequent scission of the envelope by a protein ring, the Z-ring. MatP is a DNA binding protein that contributes both to the positioning of the Z-ring at midcell and the temporal control of nucleoid segregation. Our integrated in vivo and in vitro analysis provides evidence that MatP can interact with lipid membranes comprising the phospholipid mixture in the E. coli inner membrane, without concomitant recruitment of the short DNA sequences specifically targeted by MatP. This observation strongly suggests that the membrane may play a role in the regulation of the function and localization of MatP, which could be relevant for the coordination of the two fundamental processes in which this protein participates, nucleoid segregation and cell division.

biochemistry↗