Nagao, P. E. | bioRxiv Science

bioRxiv2023

Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract

Type VIIb secretion systems (T7SSb) in Gram-positive bacteria facilitate physiology, interbacterial competition, and/or virulence via EssC ATPase-driven secretion of small [a]-helical proteins and toxins. Recently, we characterized T7SSb in group B Streptococcus (GBS), a leading cause of infection in newborns and immunocompromised adults. GBS T7SS comprises four subtypes based on variation in the C-terminus of EssC and the repertoire of downstream effectors; however, the intra-species diversity of GBS T7SS and impact on GBS-host interactions remains unknown. Bioinformatic analysis indicates that GBS T7SS loci encode subtype-specific putative effectors, which have low inter-species and inter-subtype homology but contain similar domains/motifs and therefore may serve similar functions. We further identify orphaned GBS WXG100 proteins. Functionally, we show that GBS T7SS subtype I and III strains secrete EsxA in vitro and that in subtype I strain CJB111, esxA1 appears to be differentially transcribed from the T7SS operon. Further, we observe subtype-specific effects of GBS T7SS on host colonization, as subtype I but not subtype III T7SS promotes GBS vaginal persistence. Finally, we observe that T7SS subtypes I and II are the predominant subtypes in clinical GBS isolates. This study highlights the potential impact of T7SS heterogeneity on host-GBS interactions.

microbiology↗

bioRxiv2021

A type VII secretion system in Group B Streptococcus mediates cytotoxicity and virulence

Type VII secretion systems (T7SS) have been identified in Actinobacteria and Firmicutes and have been shown to secrete effector proteins with functions in virulence, host toxicity, or interbacterial killing in a few genera. Bioinformatic analysis indicates that Group B streptococcal (GBS) isolates encode four distinct subtypes of T7SS machinery, three of which encode adjacent putative T7SS effectors with WXG and LXG motifs. However, the function of T7SS in GBS pathogenesis is not known. Here we show that the most abundant GBS T7SS subtype is important for virulence and cytotoxicity in brain endothelium and that these phenotypes are dependent on the WXG100 effector EsxA. We further show that the WXG motif is required for cytotoxicity in brain endothelium and that EsxA is a pore-forming protein. This work reveals the importance of a T7SS in host-GBS interactions and has implications for the functions of T7SS effectors in other Gram-positive bacteria.

microbiology↗

bioRxiv2019

The Group B Streptococcal surface antigen I/II protein, BspC, interacts with host vimentin to promote adherence to brain endothelium and inflammation during the pathogenesis of meningitis

Streptococcus agalactiae (Group B Streptococcus, GBS) normally colonizes healthy adults but can cause invasive disease, such as meningitis, in the newborn. To gain access to the central nervous system, GBS must interact with and penetrate brain or meningeal blood vessels; however, the exact mechanisms are still being elucidated. Here, we investigate the contribution of BspC, an antigen I/II family adhesin, to the pathogenesis of GBS meningitis. Disruption of the bspC gene reduced GBS adherence to human cerebral microvascular endothelial cells (hCMEC), while heterologous expression of BspC in non-adherent Lactococcus lactis conferred bacterial attachment. In a murine model of hematogenous meningitis, mice infected with {Delta}bspC mutants exhibited lower mortality as well as decreased brain bacterial counts and inflammatory infiltrate compared with mice infected with WT GBS strains. Further, BspC was both necessary and sufficient to induce neutrophil chemokine expression. We determined that BspC interacts with the host cytoskeleton component vimentin, and confirmed this interaction using a bacterial two-hybrid assay, immunofluorescent staining, and imaging flow cytometry. Vimentin null mice were protected from WT GBS infection and also exhibited less inflammatory cytokine production in brain tissue. These results suggest that BspC and the vimentin interaction is critical for the pathogenesis of GBS meningitis. AUTHOR SUMMARYGroup B Streptococcus (GBS) typically colonizes healthy adults but can cause severe disease in immune compromised individuals, including newborns. Despite wide-spread intrapartum antibiotic prophylaxis given to pregnant women, GBS remains a leading cause of neonatal meningitis. To cause meningitis, GBS must interact with and penetrate the blood-brain barrier (BBB), which separates bacteria and immune cells in the blood from the brain. In order to develop targeted therapies to treat GBS meningitis, it is important to understand the mechanisms of BBB crossing. Here, we describe the role of the GBS surface factor, BspC, in promoting meningitis and discover the host ligand for BspC, vimentin, which is an intermediate filament protein that is constitutively expressed by endothelial cells. We determined that BspC interacts with the C-terminal domain of cell-surface vimentin to promote bacterial attachment to brain endothelial cells and that purified BspC protein can induce immune signaling pathways. In a mouse model of hematogenous meningitis, we observed that a GBS mutant lacking BspC was less virulent compared to WT GBS and resulted in less inflammatory disease. We also observed that mice lacking vimentin were protected from GBS infection. These results reveal the importance of the BspC-vimentin interaction in the progression of GBS meningitis disease.

microbiology↗