Biology subjects

Hooven, T. A.

Publications and source records attributed to Hooven, T. A..

7 recordsLinked to original sources

bioRxiv2026

The bacterial cell membrane acts as a dynamic heme reservoir during group B Streptococcus bloodstream infection

During bloodstream infection, most bacterial pathogens maintain homeostatic levels of heme, which serves as an essential biochemical cofactor and iron source, but becomes toxic at high intracellular concentrations. Well-characterized, surface exposed heme binding and acquisition systems exist in several blood-borne bacterial species. However, some gram-positive bacteria that invade the bloodstream do not encode surface displayed heme acquisition systems, despite showing clear evidence of heme utilization in blood. An example is Streptococcus agalactiae (group B Streptococcus; GBS), which is a major cause of infection in neonatal and immunocompromised populations. Here we show that GBS uses its cell membrane as a dynamic heme reservoir, which functions as the primary site of environmental heme capture, sensing, and transmembrane flux. Using positive and negative genetic selection screens, targeted mutagenesis, membrane fractionation, and spectroscopic heme detection and binding assays, we demonstrate that heme is partitioned into the GBS cell membrane, where it is sensed by the histidine kinase HssS and extracted for intracellular use by the CydDC transporter. Genetically disrupting the function of either HssS heme sensing or CydDC membrane heme extraction attenuates bacterial survival in human whole blood and in a mouse model of bacteremia. These results suggest that cell membrane-localized heme homeostasis is a determinant of fitness during blood survival. This work expands the current models of bacterial heme physiology and provides evidence that membrane localized, homeostatic heme reservoirs may represent an underrecognized strategy for blood-borne pathogens that lack canonical heme acquisition systems.

microbiology↗

bioRxiv2025

CRISPR interference in a Streptococcus agalactiae Multi-locus Sequence Type 17 Strain

Group B Streptococcus (GBS), a common colonizer of the human genital and gastrointestinal tracts, is a leading cause of neonatal bacterial meningitis, which can lead to severe neurological complications. The hypervirulent serotype III, sequence type 17 (ST-17) strain COH1 is strongly associated with late-onset disease due to its unique set of virulence factors. However, genetic manipulation of ST-17 strains is notoriously challenging, limiting the ability to study key pathogenic genes. In this study, we developed a CRISPR interference (CRISPRi) system utilizing an endogenous catalytically inactivated Cas9 (dCas9) in the COH1 strain, enabling targeted and tunable gene expression knockdown. We confirmed the efficacy of this system through hemolysis assays, qPCR transcriptional analysis, and in vitro infection models using human brain endothelial cells. The CRISPRi system successfully produced phenotypic knockdowns of essential virulence genes, including pilA, srr2, and iagA, reducing adhesion, invasion, and inflammatory responses at the blood-brain barrier. This platform enables rapid gene knockdowns for functional genomics in ST-17 GBS, enabling high-throughput screening and pathogenesis research. ImportanceGroup B Streptococcus (GBS) remains the worlds leading cause of neonatal meningitis. GBS-host interactions at the blood-brain barrier (BBB) are dependent on bacterial factors, including surface factors and two-component systems. Multi-locus sequence type 17 (ST-17) GBS strains are highly associated with neonatal meningitis, and these strains harbor many virulence factors for infection at the BBB. Historically, these factors have been studied using traditional knockout mutagenesis, which has proven challenging in the most common ST-17 lab strain, COH1. This study utilizes CRISPR interference (CRISPRi) to generate rapid expression knockdown. This study validates a CRISPRi-enabled COH1 dCas9 strain as a versatile tool for probing GBS pathogenesis at the BBB.

microbiology↗

bioRxiv2025

A Cas12a Toolbox for Rapid and Flexible Group B Streptococcus Genomic Editing and CRISPRi

Streptococcus agalactiae (group B Streptococcus; GBS) is a leading cause of neonatal sepsis and meningitis. Despite advances in molecular microbiology, GBS genome engineering remains laborious due to inefficient mutagenesis protocols. Here, we report a versatile and rapid Cas12a-based toolkit for GBS genetic manipulation. We developed two shuttle plasmids--pGBSedit for genome editing and pGBScrispri for inducible CRISPR interference--derived from an Enterococcus faecium system and optimized for GBS. Using these tools, we achieved targeted gene insertions, markerless deletions, and efficient, template-free mutagenesis via alternative end-joining repair. Furthermore, a catalytically inactive dCas12a variant enabled inducible gene silencing, with strand-specific targeting effects. The system demonstrated broad applicability across multiple GBS strains and minimal off-target activity, as confirmed by whole-genome sequencing. This Cas12a-based platform offers a rapid, flexible, and scalable approach to genetic studies in GBS, facilitating functional genomics and accelerating pathogenesis research.

microbiology↗

bioRxiv2024

A CRISPRi Library Screen in Group B Streptococcus Identifies Surface Immunogenic Protein (Sip) as a Mediator of Multiple Host Interactions

Group B Streptococcus (GBS; Streptococcus agalactiae) is an important pathobiont capable of colonizing various host environments, contributing to severe perinatal infections. Surface proteins play critical roles in GBS-host interactions, yet comprehensive studies of these proteins functions have been limited by genetic manipulation challenges. This study leveraged a CRISPR interference (CRISPRi) library to target genes encoding surface-trafficked proteins in GBS, identifying their roles in modulating macrophage cytokine responses. Bioinformatic analysis of 654 GBS genomes revealed 66 conserved surface protein genes. Using a GBS strain expressing chromosomally integrated dCas9, we generated and validated CRISPRi strains targeting these genes. THP-1 macrophage-like cells were exposed to ethanol-killed GBS variants, and pro-inflammatory cytokines TNF- and IL-1{beta} were measured. Notably, knockdown of the sip gene, encoding the Surface Immunogenic Protein (Sip), significantly increased IL-1{beta} secretion, implicating Sip in caspase-1-dependent regulation. Further, {Delta}sip mutants demonstrated impaired biofilm formation, reduced adherence to human fetal membranes, and diminished uterine persistence in a mouse colonization model. These findings suggest Sip modulates GBS- host interactions critical for pathogenesis, underscoring its potential as a therapeutic target or vaccine component.

microbiology↗

bioRxiv2023

Diet influences community dynamics following vaginal group B Streptococcus colonization

The vaginal microbiota plays a pivotal role in reproductive, sexual, and perinatal health and disease. Unlike the well-established connections between diet, metabolism, and the intestinal microbiota, parallel mechanisms influencing the vaginal microbiota and pathogen colonization remain overlooked. In this study, we combine a mouse model of Streptococcus agalactiae strain COH1 (GBS) vaginal colonization with a mouse model of pubertal-onset obesity to assess diet as a determinant of vaginal microbiota composition and its role in colonization resistance. We leveraged culture-dependent assessment of GBS clearance and culture-independent, sequencing-based reconstruction of the vaginal microbiota in relation to diet, obesity, glucose tolerance, and microbial dynamics across time scales. Our findings demonstrate that excessive body weight gain and glucose intolerance are not associated with vaginal GBS density or timing of clearance. Diets high in fat and low in soluble fiber are associated with vaginal GBS persistence, and changes in vaginal microbiota structure and composition due to diet contribute to GBS clearance patterns in nonpregnant mice. These findings underscore a critical need for studies on diet as a key determinant of vaginal microbiota composition and its relevance to reproductive and perinatal outcomes. IMPORTANCEThis work sheds light on diet as a key determinant influencing the composition of vaginal microbiota and its involvement in group B Streptococcus (GBS) colonization in a mouse model. The study shows that dietary components, such as dietary fat and soluble fiber, impact GBS density and timing of clearance in the female reproductive tract. These findings are particularly significant given clear links between GBS and adverse reproductive and neonatal outcomes, advancing our understanding by identifying critical connections between dietary components, factors originating from the intestinal tract, vaginal microbiota, and reproductive outcomes.

microbiology↗

bioRxiv2023

Group B Streptococcus Cas9 variants provide insight into programmable gene repression and CRISPR-Cas transcriptional effects

Group B Streptococcus (GBS; S. agalactiae) causes chorioamnionitis, neonatal sepsis, and can also cause disease in healthy or immunocompromised adults. GBS possesses a type II-A CRISPR-Cas9 system, which defends against foreign DNA within the bacterial cell. Several recent publications have shown that GBS Cas9 influences genome-wide transcription through a mechanism uncoupled from its function as a specific, RNA-programmable endonuclease. We examine GBS Cas9 effects on genome-wide transcription through generation of several isogenic variants with specific functional defects. We compare whole-genome RNA-seq from {Delta}cas9 GBS with a full-length Cas9 gene deletion; dcas9 defective in its ability to cleave DNA but still able to bind to frequently occurring protospacer adjacent motifs; and scas9 that retains its catalytic domains but is unable to bind protospacer adjacent motifs. Comparing scas9 GBS to the other variants, we identify nonspecific protospacer adjacent motif binding as a driver of genome-wide, Cas9 transcriptional effects in GBS. We also show that Cas9 transcriptional effects from nonspecific scanning tend to influence genes involved in bacterial defense and nucleotide or carbohydrate transport and metabolism. While genome-wide transcription effects are detectable by analysis of next-generation sequencing, they do not result in virulence changes in a mouse model of sepsis. We also demonstrate that catalytically inactive dCas9 expressed from the GBS chromosome can be used with a straightforward, plasmid-based, single guide RNA expression system to suppress transcription of specific GBS genes without potentially confounding off-target effects. We anticipate that this system will be useful for study of nonessential and essential gene roles in GBS physiology and pathogenesis.

microbiology↗

bioRxiv2018

A counterselectable sucrose sensitivity marker permits efficient and flexible mutagenesis in Streptococcus agalactiae

Streptococcus agalactiae (group B Streptococcus; GBS) is a cause of severe infections, particularly during the newborn period. While methods exist for generating chromosomal mutations in GBS, they are cumbersome and inefficient and present significant challenges if the goal is to study subtle mutations such as single base pair polymorphisms. To address this problem, we have developed an efficient and flexible GBS mutagenesis protocol based on sucrose counterselection against levansucrase (SacB) expressed from a temperature-selective shuttle vector. GBS containing the SacB expression cassette demonstrate lethal sensitivity to supplemental sucrose whether the plasmid DNA is replicating outside of the chromosome or has been integrated during a crossover event. Transmission electron microscopy shows that SacB-mediated lethal sucrose sensitivity results from accumulation of inclusion bodies that eventually lead to complete degradation of normal cellular architecture and subsequent lysis. We used this new mutagenesis technique to generate an in-frame, allelic exchange knockout of the GBS sortase gene srtA, demonstrating that >99% of colonies that emerge from our protocol had the expected knockout phenotype and that among a subset tested by sequencing, 100% had the correct genotype. We also generated barcoded nonsense mutations in the cylE gene in two GBS strains, showing that the approach can be used to make small, precise chromosomal mutations.\n\nImportanceThe ability to generate chromosomal mutations is fundamental to microbiology. Historically, however, GBS pathogenesis research has been made challenging by the relative genetic intractability of the organism. Generating a single knockout in GBS using traditional techniques can take many months, with highly variable success rates. Furthermore, traditional methods do not offer a straightforward way to generate single base pair polymorphisms or other subtle changes, especially to noncoding regions of the chromosome. We have developed a new sucrose counterselection-based method that permits rapid, efficient, and flexible GBS mutagenesis. Our technique requires no additional equipment beyond what is needed for traditional approaches. We believe that it will catalyze rapid advances in GBS genetics research by significantly easing the path to generating mutants.

microbiology↗