Biology subjects

Lehmann, E.

Publications and source records attributed to Lehmann, E..

7 recordsLinked to original sources

bioRxiv2025

Phage resistance impacts antibiotic susceptibility and virulence in Staphylococcus aureus

As antibiotic resistance continues to rise worldwide, phage therapy offers a promising solution by harnessing viruses that infect and kill bacteria. However, phage-resistance may develop, compromising therapy. Phage-resistance has primarily been linked to changes in major phage receptors that for the human pathogen Staphylococcus aureus are the cell-wall linked wall teichoic acids (WTA). To identify additional factors contributing to phage-resistance, S. aureus was evolved under selective pressure from lytic phages, including candidates from therapeutic phage cocktails, to obtain resistant clones. A third of the phage-resistant clones acquired mutations associated with cell-wall changes previously linked with phage resistance, namely in femA, involved in peptidoglycan crossbridge formation, and tagO, encoding the initiator of the WTA biosynthesis. The remaining clones had mutations in pathways not previously associated with phage-resistance, including nucleoside catabolism (deoC1), polyamine import (potAB) and DNA/RNA replication (cshA, ligA), suggesting that phage-resistance may be associated with phage-driven host takeover. Antibiotic susceptibility and virulence were diversely affected by the mutations; mutations in tagO increased {beta}-lactams sensitivity and attenuated virulence, whereas mutations in femA/ligA or cshA increased staphylococcal virulence in Galleria mellonella. This work demonstrates the involvement of several novel bacterial pathways in phage resistance, highlighting the complexity behind phage-bacterial interactions.

microbiology↗

bioRxiv2025

A potential role of altered SIgA-targeting of gut microbiota in long-term dysbiosis in pediatric solid organ transplant recipients

BackgroundComposition of gut microbiota (GM) is altered in solid organ transplantation (SOT) patients, where the degree of dysbiosis is associated with long-term survival. Factors governing dysbiosis are poorly understood with immunosuppression therapy believed to be involved in altering GM composition in those patients, either directly or via the immune system. At the interface stands secretory (S)IgA, however, little is known on its role governing dysbiosis in the context of SOT. In this study, we performed quantitative metagenomic analyses of GM accompanied by SIgA sequencing in 48 pediatric SOT recipients (age = 10.6 {+/-} 4.7 years) receiving either a heart (HTR, n=10), a kidney (KTR, n=11) or a liver (LTR, n=27) and compared results to healthy controls (HC, n=16). ResultsWe confirmed compositional and functional dysbiosis in SOT patients that broadly clustered into two groups, where cluster 1 (n=23) comprised most LTR patients and was closer to HC compared with cluster 2 (n=24) that exhibited stronger dysbiosis and included most HTR and KTR patients. The degree of dysbiosis was associated with Tacrolimus (TAC) levels. Overall, patients exhibited higher SIgA levels than HC, along with an increased percentage of bacteria targeted and altered target spectra. Furthermore, altered SIgA responses were associated with the degree of dysbiosis and were especially increased in cluster 2, in particular in HTR patients. A mechanistic model connecting immunosuppression, GM composition and SIgA targeting is proposed. ConclusionOur study suggests that altered SIgA responses play an important role for GM alterations observed in SOT patients. It opens new therapeutic angles to combat GM dysbiosis and associated long-erm complications.

microbiology↗

bioRxiv2024

The two-component system ArlRS is essential for wall teichoic acid glycoswitching in Staphylococcus aureus

Staphylococcus aureus is among the leading causes of hospital-acquired infections. Critical to S. aureus biology and pathogenesis are the cell wall-anchored glycopolymers wall teichoic acids (WTA). Approximately one-third of S. aureus isolates decorates WTA with a mixture of 1,4- and {beta}1,4-N-acetylglucosamine (GlcNAc), which requires the dedicated glycosyltransferases TarM and TarS, respectively. Environmental conditions, such as high salt concentrations, affect the abundance and ratio of 1,4- and {beta}1,4-GlcNAc WTA decorations, thereby impacting biological properties such as antibody binding and phage infection. To identify regulatory mechanisms underlying WTA glycoswitching, we screened 1,920 S. aureus mutants (Nebraska Transposon Mutant Library) by immunoblotting for differential expression of WTA-linked 1,4- or {beta}1,4-GlcNAc using specific monoclonal antibody Fab fragments. Three two-component systems (TCS), GraRS, ArlRS, and AgrCA, were among the 230 potential hits. Using isogenic TCS mutants, we demonstrated that ArlRS is essential for WTA {beta}1,4-GlcNAc decoration through regulation of tarM but not tarS. ArlRS regulated tarM expression through the transcriptional regulator MgrA, which was responsive to Mg2+, but not Na+. Importantly, ArlRS-mediated regulation of WTA glycosylation affected S. aureus interaction with the innate receptor langerin and lysis by {beta}1,4-GlcNAc-dependent phages. Since WTA represents a promising target for future immune-based treatments and vaccines, our findings provide important insight to align targeting strategies with the S. aureus WTA glycosylation patterns during infection. ImportanceStaphylococcus aureus is a common colonizer of mucosal surfaces, but is also a frequent cause of severe infections in humans. Development of antibiotic resistance complicates treatment of S. aureus infections, increasing the need for antibiotic alternatives such as vaccines and therapies with bacterial viruses also known as phages. Wall teichoic acids (WTA) are abundantly-expressed glycosylated structures of the S. aureus cell wall that have gained attention as a promising target for new treatments. Importantly, WTA glycosylation patterns show variation depending on environmental conditions, thereby impacting phage binding and interaction with host factors, such as antibodies and innate pattern-recognition receptors. Here, we show that the two-component system ArlRS through its effector MgrA is involved in regulation of WTA glycosylation by responding to environmental changes in Mg2+ concentration. These findings may support the design of new treatment strategies that target WTA glycosylation patterns of S. aureus during infection.

microbiology↗

bioRxiv2024

Systematic classification of phage receptor-binding proteins predicts surface glycopolymer structure in Staphylococcus pathogens

Wall teichoic acids (WTAs) are major surface polymers of staphylococcal pathogens and commensals, whose variable structure governs interaction with host receptors, immunoglobulins, and bacteriophages. The ribitol phosphate (RboP) WTA type contributes to virulence, for instance in Staphylococcus aureus, but we lack comprehensive knowledge of WTA types and cognate phages. We developed a computational pipeline to identify the receptor-binding proteins (RBPs) in 335 Staphylococcus phage genomes, yielding multiple distinct RBP clusters. Notably, many phages had two separate RBPs with in part different WTA preferences. RBP representatives differed in specificity for RboP WTA glycosylation types, recapitulating the specificity of the corresponding phage. Based on these results, we created a publicly available bioinformatic tool to predict phage host specificity based on RBP similarity. The RboP WTA specific {Phi}13-RBP also revealed that the presence of RboP WTA on non-aureus staphylococci is more common than previously thought. Our approach facilitates the characterization of opportunistic Staphylococcus pathogens according to WTA types, which has major implications for phage-mediated interspecies horizontal gene transfer and future phage therapies.

microbiology↗

bioRxiv2023

The capsular polysaccharide obstructs wall teichoic acid functions in Staphylococcus aureus

BackgroundThe cell envelope of Staphylococcus aureus contains two major secondary cell wall glycopolymers: capsular polysaccharide (CP) and wall teichoic acid (WTA). Both the CP and the WTA are attached to the cell wall and play distinct roles in S. aureus colonization, pathogenesis, and bacterial evasion of host immune defenses. ObjectiveWe aimed to investigate whether CP interferes with WTA-mediated properties. MethodsStrains with natural heterogeneous expression of CP, strains with homogeneous high CP expression and CP-deficient strains were compared to WTA deficient controls regarding WTA dependent phage binding, cell adhesion, IgG deposition, and virulence in vivo. ResultsWTA-mediated phage adsorption, specific antibody deposition and cell adhesion were negatively correlated with CP expression. WTA, but not CP, enhanced the bacterial burden in a mouse abscess model, while CP overexpression resulted in intermediate virulence in vivo. ConclusionsCP protects the bacteria from WTA-dependent opsonization and phage binding. This protection comes at the cost of diminished adhesion to host cells. The highly complex regulation and mostly heterogeneous expression of CP has probably evolved to ensure the survival and optimal physiological adaptation of the bacterial population as a whole.

microbiology↗

bioRxiv2022

Phase separation of hnRNP A1 upon specific RNA-binding observed by magnetic resonance

Interaction of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) with specific single-stranded RNA and its relation to liquid-liquid phase separation were investigated in vitro by magnetic resonance based on site-directed spin labelling. An ensemble model of free hnRNP A1 in the absence of RNA was derived from distance distributions between spin labelled sites and small angle X-ray scattering. This model revealed a compact state of the low-complexity domain and interaction of this domain with the RNA recognition motifs. Paramagnetic relaxation enhancement NMR spectroscopy confirmed this interaction. The addition of RNA to dispersed solutions of hnRNP A1 induced phase separation, observed by formation of liquid droplets. The phase separation depended on the RNA concentration and sequence, with continuous wave EPR spectroscopy showing that local protein dynamics is affected by point mutations in the RNA sequence. We propose that an interplay of sequence-specific RNA binding and phase transition serves as a regulatory mechanism for RNA segregation in the stress response of cells.

molecular biology↗

bioRxiv2020

A proteogenomics workflow to uncover the world of small proteins in Staphylococcus aureus

Small proteins play diverse and essential roles in bacterial physiology and virulence. Despite their importance, automated genome annotation algorithms still cannot accurately annotate all respective small open reading frames (sORFs), as they usually provide insufficient sequence information for domain and homology searches, tend to be species specific and only a few experimentally validated examples are covered in standard proteomics studies. The accuracy and reliability of genome annotations, particularly for sORFs, can be significantly improved by integrating protein evidence from experimental approaches that enrich for small proteins. Here we present a highly optimized and flexible workflow for bacterial proteogenomics, which covers all steps from (i) creation of protein databases, (ii) database searches, (iii) peptide-to-genome mapping to (iv) result interpretation and whose automated execution is supported by two open source tools (SALT & Pepper). We used the workflow to identify high quality peptide spectrum matches (PSMs) for both annotated and unannotated small proteins ([≤] 100 aa; SP100) in Staphylococcus aureus Newman. Proteins isolated from cells at the exponential and stationary growth phase were digested with different endopeptidases (trypsin, Lys-C, AspN), the resulting peptides fractionated by gel-based and gel-free methods and measured with highly sensitive mass spectrometers. PSMs or sORF predictions from sORFfinder were stringently filtered allowing us to detect 185 soluble SP100, 69 of which were missing in the used genome annotation. Most interestingly, almost half of the identified SP100 were basic, suggesting a role in binding to more acidic molecules such as nucleic acids or phospholipids. In addition, phage-related functions were proposed for 30 SP100, based on the localization of their coding sequences in the genome.

genomics↗