Biology subjects

Bojer, M. S.

Publications and source records attributed to Bojer, M. S..

9 recordsLinked to original sources

bioRxiv2026

Human airway model reveals host-pathogen co-infection dynamics of Staphylococcus aureus and Pseudomonas aeruginosa

Polymicrobial airway infections, particularly those involving Staphylococcus aureus and Pseudomonas aeruginosa, are a hallmark of severe chronic respiratory diseases such as those in people with cystic fibrosis (pwCF). Yet, the mechanisms enabling their co-existence remain poorly understood. Using a human air-liquid interface (ALI) airway model, we dissected host-pathogen and interspecies dynamics during mono- and co-infections with clinically relevant bacterial pathogens. We found that S. aureus strains exhibited distinct colonization patterns and virulence profiles, with the deletion of the agr quorum sensing locus leading to attenuated epithelial disruption. Additionally, the H1 component of P. aeruginosas type VI secretion system was critical for competitive exclusion of S. aureus, its deletion allowing for occasional co-localization of both species. Importantly, co-infection timing strongly influenced pathogen dominance and epithelial damage, with pre-colonization of ALI models with S. aureus prior to P. aeruginosa infection, mimicking clinical observations in CF. Our results reveal that strain-specific traits and secretion systems influence microbial competition and persistence in the airway and underscore the importance of physiologically relevant models for studying chronic infections. Moreover, they provide the foundation for exploring therapeutic strategies for polymicrobial infections that account for the colonization sequence and microbial evolution for treatment design.

microbiology↗

bioRxiv2025

Inhibition of agr Quorum Sensing in Staphylococci by Novel Thiazole-Indole Hybrid Compounds

The rise of multidrug-resistant Staphylococcus aureus has prompted the search for innovative, non-bactericidal therapeutic strategies. Anti-virulence approaches targeting quorum sensing (QS) pathways offer a promising alternative by disarming pathogenicity, potentially without exerting selective pressure for resistance. In this study, we report the identification of two novel thiazole-indole hybrid compounds, namely 2-[(6-methoxy-1H-indol-2-yl)methyl]-5-cyano-1,3-thiazol-3-amine (designated C3) and 3-amino-5-cyano-2-(5-chloro-1H-indol-2-yl) thiazole (designated C4), as potent inhibitors of the S. aureus accessory gene regulator (agr) quorum sensing system. Building on two heterocyclic scaffolds commonly used in medicinal chemistry and associated with QS modulation, these synthetic small molecules act on the S. aureus AgrC QS receptor, attenuating virulence without affecting bacterial viability. Both compounds significantly reduced the production of secreted virulence factors without promoting biofilm formation, a known drawback of some other QS inhibitors. Furthermore, their activity extended to Staphylococcus lugdunensis, while sparing the commensal Staphylococcus epidermidis, indicating pathogen-selective QS interference. These findings establish novel thiazole-indole hybrids as a promising chemotype for anti-virulence intervention and provide valuable chemical tools for probing agr-mediated regulation in Staphylococcus species.

microbiology↗

bioRxiv2025

Temperature-dependent regulation of bacterial cell division hydrolases by the coordinated action of a regulatory RNA and the ClpXP protease

A defining feature of bacteria is the peptidoglycan cell wall which provides structural integrity and prevents osmotic lysis. While peptidoglycan hydrolases are required for daughter cell separation, dysregulated cell wall degradation may result in cell lysis. The mechanisms allowing bacteria to control these deadly enzymes in response to environmental changes remain incompletely understood. Here, we find that in Staphylococcus aureus, temperature-dependent regulation of such hydrolases occurs by the coordinated action of a CHAP domain-specific regulatory RNA and the ClpXP protease. Using a proteomics approach, we identify a hitherto uncharacterized ClpXP controlled autolysin, CxcA, with a catalytic CHAP domain and show that it contributes to separation of daughter cells. CxcA is positively controlled by a non-coding RNA, named Rbc1 (for RNA binding to CHAP domain) transcribed from the antisense strand of cxcA. Notably, Rbc1 is capable of base pairing with RNAs encoding the CHAP domains of numerous cell wall hydrolases and we show that Rbc1 works in trans to upregulate the cell division hydrolase Sle1. Specifically, Rbc1 functions as a thermosensor allowing for upregulation of CxcA and Sle1 at low temperature where daughter cell separation is impeded. Interestingly, the Rbc1-mediated up-regulation of CxcA and Sle1 does not involve mRNA stabilization or increased translation; instead, Rbc1 depletion increases ClpXP-mediated degradation. In conclusion, we identify a novel cell division hydrolase that is highly conserved in Staphylococci and show that it is co-regulated with enzymes containing the catalytic CHAP domain via transcriptional regulation, an RNA-RNA temperature sensory mechanism and the ClpXP protease.

microbiology↗

bioRxiv2025

Mapping of Quorum Sensing Landscape of Commensal and Pathogenic Staphylococci Reveals a Largely Inhibitory Interaction Network

Staphylococci utilize secreted autoinducing peptides (AIPs) to regulate group behaviour through a process called quorum sensing (QS). For staphylococcal pathogens such as S. aureus, QS regulates expression of major virulence factors and QS inhibition has been proposed as an alternative to antibiotics for treatment of infections with methicillin resistant S. aureus (MRSA). Here, we surveyed the interaction map between QS systems of the pathogens Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus lugdunensis and the 36 currently known AIPs from 22 staphylococcal species. We identified seven of these ribosomally synthesized and post-translationally modified peptides (RiPPs) in this study and all synthetic peptides were assessed for their ability to modulate QS. The mapped interactions of >280 native QS pairings were divided into human- and animal-associated staphylococci showing substantial differences in inhibitory potencies between the groups. In particular, AIPs of the bovine-associated species S. simulans displayed potential as QS inhibitors in the strains investigated in this study and were therefore chosen as starting point for a structure-activity relationship study. This study provides insights into the requirements for QS interference, yielding the most potent inhibitors reported to date for S. epidermidis and S. lugdunensis. Further, we tested an S. simulans AIP as anti-virulence agent in an assay to assess risk of acquired suppression of the inhibitory effect, and we established an assay set-up to successfully monitor agr deactivation of virulent MRSA by the QS inhibitor. Finally, a peptide was shown to attenuate skin infection caused by MRSA in a mouse model. Our results reveal a complex network of staphylococcal interactions and provide further impetus for the development of therapeutic strategies, based on QS modulation to target antibiotic-resistant pathogens. TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/635662v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@f2be0aorg.highwire.dtl.DTLVardef@9aa0c2org.highwire.dtl.DTLVardef@1b02c26org.highwire.dtl.DTLVardef@12273a7_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

A collection of diverse bacteriophages for biocontrol of ESBL- and AmpC-β-lactamase-producing E. coli

Novel solutions are needed to reduce the risk of transmission of extended spectrum {beta}-lactamase and AmpC {beta}-lactamase producing Escherichia coli (ESBL/AmpC E. coli) in livestock to humans. Since phages are promising biocontrol agents, we established a collection of 28 phages against ESBL/AmpC E. coli and showed by whole genome sequencing that all phages were unique and could be assigned to 15 different genera. Host range analysis showed that 82% of 198 strains, representing the genetic diversity of ESBL/AmpC E. coli, were sensitive to at least one phage. Identifying receptors used for initial binding experimentally as well as in silico predictions, allowed us to combine phages into two different cocktails with broad host range targeting diverse receptors. These phage cocktails inhibit growth and kill ESBL/AmpC E. coli in vitro, thus suggesting the potential of phages as promising biocontrol agents. HIGHLIGHTSO_LI28 unique phages infecting ESBL/AmpC E. coli were isolated and characterized C_LIO_LIBroad host range phages targeting different receptors were used to compose phage cocktails C_LIO_LIPhage cocktails efficiently inhibit growth of ESBL/AmpC E. coli in vitro C_LI

microbiology↗

bioRxiv2023

Development of Stabilized Peptide Analogues to Study a Short-lived Peptide Signal that Regulates Cell-to-Cell Communication in Listeria monocytogenes

Quorum sensing (QS) is a mechanism that regulates group behavior in bacteria, and in Gram-positive bacteria, the communication molecules are often cyclic peptides, called autoinducing peptides (AIPs). We recently showed that pentameric thiolactone-containing AIPs from Listeria monocytogenes, and from other species, spontaneously undergo rapid rearrangement to homodetic cyclopeptides, which hampers our ability to study the activity of these short-lived compounds. Here, we developed chemically modified analogues that closely mimic the native AIPs while remaining structurally intact, by introducing N-methylation or thioester-to-thioether substitutions. The stablilized AIP analogues exhibit strong QS agonism in L. monocytogenes and allow structure-activity relationships to be studied. Our data provide evidence that loudly suggest that the most potent AIP is in fact the very short-lived thiolactone-containing pentamer. Further, we find that the QS system in L. monocytogenes is more promiscuous with respect to the structural diversity allowed for agonistic AIPs than reported for the more extensively studied QS systems in Staphylococcus aureus and Staphylococcus epidermidis. The developed compounds will be important for uncovering the biology of L. monocytogenes, and the design principles should be broadly applicable to the study of AIPs in other species.

microbiology↗

bioRxiv2023

Cross-species communication via agr controls phage susceptibility in Staphylococcus aureus

Bacteria and their viruses (phages) use quorum sensing (QS) systems to coordinate group behavior. In Staphylococcus aureus, QS plays a critical role in the transition from colonization to infection and involves the accumulation of auto-inducing peptides (AIPs). Humans and animals are also colonized by non-aureus staphylococci (NAS) that produce AIPs, many of which inhibit S. aureus QS. We found that QS induction is necessary for S. aureus susceptibility to the lytic phage, Stab20 and that in mixed communities with NAS producing inhibitory AIPs, S. aureus is protected from phage infection. The primary phage receptors in S. aureus are wall teichoic acids (WTA) substituted with - and/or {beta}-linked N- acetylglucosamine (GlcNAc). We show that QS induction reduces -GlcNAc substitutions and enables Stab20 infection through binding to {beta}-glycosylated WTA. However, in the presence of inhibitory AIPs or during co-culture with NAS, QS induction and Stab20 infection are impeded. Our results highlight how cross-species communication can significantly impact bacterial susceptibility to phages and may explain occasional failures observed when phages are used as antimicrobials in for example phage therapy.

microbiology↗

bioRxiv2021

Chemical phylogenetics of the staphylococcal quorum sensing landscape

Staphylococci utilize secreted autoinducing peptides (AIPs) to regulate group behaviour through a process called quorum sensing (QS). Here, we survey the QS interaction landscape within the Staphylococcus genus by assembling a unique compound collection, comprising all the currently known AIPs. These ribosomally synthesized and posttranslationally modified peptides (RiPPs) were obtained by chemical synthesis and mapping of their ability to modulate QS was evaluated using reporter strains of common human and animal colonizing pathogens (S. aureus, S. epidermidis, S. lugdunensis). The resulting map of >200 native QS interactions provides a holistic view of nodes that contribute to the complex signalling network within the Staphylococcus genus. This overview reveals surprising cross-species QS induction and identify the first pan-inhibitory AIP, which is then shown to attenuate MRSA induced skin infection in a mouse model. Our results expose a complex universe of possible staphylococcal interactions and provide further impetus for development of therapeutics based on QS modulators targeting antibiotic resistant pathogens.

microbiology↗

bioRxiv2018

SosA inhibits cell division in Staphylococcus aureus in response to DNA damage

Inhibition of cell division is critical for cell viability under DNA damaging conditions. In bacterial cells, DNA damage induces the SOS response, a process that inhibits cell division while repairs are being made. In coccoid bacteria, such as the human pathogen Staphylococcus aureus, the process remains poorly understood. Here we have characterized an SOS-induced cell-division inhibitor, SosA, in S. aureus. We find that in contrast to the wildtype, sosA mutant cells continue division under DNA damaging conditions with decreased viability as a consequence. Conversely, overproduction of SosA leads to cell division inhibition and reduced growth. The SosA protein is localized in the bacterial membrane and mutation of an extracellular amino acid, conserved between homologs of other staphylococcal species, abolished the inhibitory activity as did truncation of the C-terminal 30 amino acids. In contrast, C-terminal truncation of 10 amino acids lead to SosA accumulation and a strong cell division inhibitory activity. A similar phenotype was observed upon expression of wildtype SosA in a mutant lacking the membrane protease, CtpA. Thus, the extracellular C-terminus of SosA is required both for cell-division inhibition and for turnover of the protein. Functional studies showed that SosA is likely to interact with one or more divisome components and, without interfering with early cell-division events, halts cell division at a point where septum formation is initiated yet being unable to progress to septum closure. Our findings provide important insights into cell-division regulation in staphylococci that may foster development of new classes of antibiotics targeting this essential process. ImportanceStaphylococcus aureus is a serious human pathogen and a model organism for cell-division studies in spherical bacteria. We show that SosA is the DNA-damage-inducible cell-division inhibitor in S. aureus that upon expression causes cell swelling and cessation of the cell cycle at a characteristic stage post septum initiation but prior to division plate completion. SosA appears to function via an extracellular activity and is likely to do so by interfering with the essential membrane-associated division proteins, while at the same time being negatively regulated by the membrane protease CtpA. This report represents the first description of the process behind cell-division inhibition in coccoid bacteria. As several pathogens are included in this category, uncovering the molecular details of SosA activity and control can lead to identification of new targets for development of valuable anti-bacterial drugs.

microbiology↗