Biology subjects

Joyce, L. R.

Publications and source records attributed to Joyce, L. R..

4 recordsLinked to original sources

bioRxiv2022

Comparative genomics of Streptococcus oralis identifies large scale homologous recombination and a genetic variant associated with infection

The viridans group streptococci (VGS) are a large consortium of commensal streptococci that colonize the human body. Many species within this group are opportunistic pathogens causing bacteremia and infective endocarditis (IE), yet little is known about why some strains cause invasive disease. Identification of virulence determinants is complicated by the difficulty of distinguishing between the closely related species of this group. Here, we analyzed genomic data from VGS isolated from patient blood cultures with invasive infections and from oral swabs of healthy volunteers and determined the best performing methods for species identification. Using whole-genome sequence data, we characterized the population structure of a diverse sample of Streptococcus oralis isolates and found evidence of frequent recombination. We used multiple genome-wide association study tools to identify candidate determinants of invasiveness. These tools gave consistent results, leading to the discovery of a single synonymous single nucleotide polymorphism (SNP) that was significantly associated with invasiveness. This SNP is within a previously undescribed gene that is conserved across the majority of VGS species. Using growth in the presence of human serum and a simulated infective endocarditis vegetation model, we were unable to identify a phenotype for the enriched allele in laboratory assays, suggesting a phenotype may be specific to natural infection. These data highlight the power of analyzing natural populations for gaining insight into pathogenicity, particularly for organisms with complex population structures like the VGS. ImportanceThe viridians group streptococci (VGS) are a large collection of closely related commensal streptococci, with many being opportunistic pathogens causing invasive diseases such as bacteremia and infective endocarditis. Little is known about virulence determinants in these species, and there is a distinct lack of genomic information available for the VGS. In this study, we collected VGS isolates from invasive infections and healthy volunteers and performed whole genome sequencing for a suite of downstream analyses. We focused on a diverse sample of Streptococcus oralis genomes and identified high rates of recombination in the population as well as a single genome variant highly enriched in invasive isolates. The variant lies within a previously uncharacterized gene, nrdM, which shares homology with the anaerobic ribonucleoside triphosphate reductase, nrdD, and is highly conserved among VGS. This work increases our knowledge of VGS genomics and indicates that differences in virulence potential among S. oralis isolates is, at least in part, genetically determined.

microbiology↗

bioRxiv2022

Formation and function of the meninges arachnoid barrier around the developing brain

Barriers at the level of the brain endothelium, choroid plexus, and meninges strictly regulate movement of molecules and cells into and out of the central nervous system (CNS). In contrast to the blood-brain barrier and choroid plexus epithelial barrier, developmental timing and function of the meningeal arachnoid barrier, a layer of epithelial-like cells connected by tight and adherens junctions, is largely unknown. To begin to address this, we mined our E14.5 mouse single cell transcriptomic (scRNA-seq) meningeal fibroblast data set and identified the repression of Wnt-{beta}-catenin signaling as a key mechanism underlying the specification of epithelial-like arachnoid barrier cells from Collagen 1+ and Crabp2+ mesenchymal meningeal precursors. We show that elevating Wnt-{beta}-catenin signaling in prenatal meningeal mesenchymal cells prevented the development of arachnoid barrier cells. In the absence of dorsal arachnoid barrier cells, the prenatal meninges and brain are penetrable to biocytin-TMR and Streptococcus agalactiae (Group B Streptococcus, GBS), the leading pathogen known to drive life-threatening neonatal meningitis. We show that a layer of Claudin 11 (tight junction) and E-cadherin (adherens junction) expressing arachnoid barrier cells appear around the mouse brain from E13-E15 and the emergence of a functional barrier by E17 coincides with junctional localization of Claudin 11. Postnatal growth of the arachnoid barrier is marked initially by proliferation and later re-organization of junctional domains. This work provides fundamental knowledge on development and prenatal function of a meningeal arachnoid barrier, and novel tools for future studies on regional functions of this CNS barrier in the meninges.

developmental biology↗

bioRxiv2021

Streptococcus pneumoniae, S. pyogenes, and S. agalactiae membrane phospholipid remodeling in response to human serum

Streptococcus pneumoniae, S. pyogenes (Group A Streptococcus; GAS), and S. agalactiae (Group B Streptococcus; GBS) are major etiological agents of diseases in humans. The cellular membrane, a crucial site in host-pathogen interactions, is poorly characterized in streptococci. Moreover, little is known about whether or how environmental conditions influence their lipid compositions. Using normal phase liquid chromatography coupled with electrospray ionization mass spectrometry, we characterized the phospholipids and glycolipids of S. pneumoniae, GAS, and GBS in routine undefined laboratory medium, streptococcal defined medium, and, in order to mimic the host environment, defined medium supplemented with human serum. In human serum-supplemented medium, all three streptococcal species synthesize phosphatidylcholine (PC), a zwitterionic phospholipid commonly found in eukaryotes but relatively rare in bacteria. We previously reported that S. pneumoniae utilizes the glycerophosphocholine (GPC) biosynthetic pathway to synthesize PC. Through substrate tracing experiments, we confirm that GAS and GBS scavenge lysoPC, a major metabolite in human serum, thereby using an abbreviated GPC pathway for PC biosynthesis. Furthermore, we found that plasmanyl-PC is uniquely present in the GBS membrane during growth with human serum, suggesting GBS possesses unusual membrane biochemical or biophysical properties. In summary, we report cellular lipid remodeling by the major pathogenic streptococci in response to metabolites present in human serum.

microbiology↗

bioRxiv2020

Streptococcus agalactiae MprF synthesizes a novel cationic glycolipid that promotes brain entry and meningitis

Bacterial membrane lipids are critical for membrane bilayer formation, cell division, protein localization, stress responses, and pathogenesis. Despite their critical roles, membrane lipids have not been fully elucidated for many pathogens. Here, we report the discovery of a novel cationic glycolipid, Lysyl-Glucosyl-Diacylglycerol (Lys-Glc-DAG) that is synthesized in high abundance by the bacterium Streptococcus agalactiae (Group B Streptococcus, GBS). To our knowledge, Lys-Glc-DAG is more positively charged than any other known lipids. Lys-Glc-DAG carries two positive net charges per molecule, distinct from the widely described lysylated phospholipid Lysyl-phosphatidylglycerol (Lys-PG) which carries one positive net charge due to the presence of a negatively charged phosphate moiety. We use normal phase liquid chromatography (NPLC) coupled with electrospray ionization (ESI) high-resolution tandem mass spectrometry (HRMS/MS) and genetic approaches to determine that Lys-Glc-DAG is synthesized by the enzyme MprF in GBS, which covalently modifies the neutral glycolipid Glc-DAG with the cationic amino acid lysine. GBS is a leading cause of neonatal meningitis, which requires traversal of the endothelial blood-brain barrier (BBB). We demonstrate that GBS strains lacking mprF exhibit a significant decrease in the ability to invade BBB endothelial cells. Further, mice challenged with a GBS{Delta}mprF mutant developed bacteremia comparably to Wild-Type infected mice yet had less recovered bacteria from brain tissue and a lower incidence of meningitis. Thus, our data suggest that Lys-Glc-DAG may contribute to bacterial uptake into host cells and disease progression. Importantly, our discovery provides a platform for further study of cationic lipids at the host-pathogen interface.

microbiology↗