It is demonstrated that Adh2 suppresses Agr signaling and virulence gene expression while promoting a persistent phenotype, and emerges as a promising candidate for therapeutic modulation of bacterial behavior, particularly in the context of chronic wound infections.
Abstract
ABSTRACT Staphylococcus aureus is a major human pathogen whose virulence is tightly regulated by the Agr quorum sensing system. In this study, we investigated the impact of Adh2, a secreted protein from the commensal bacterium Helcococcus kunzii, on S. aureus physiology and pathogenicity. Adh2 shares structural similarity with native auto-inducing peptides (AIPs), including the conserved CDFIM motif characteristic of Agr group I. We hypothesized that Adh2 interferes with Agr signaling by competitively binding the AgrC receptor. Exposure to Adh2 significantly repressed agrA and its downstream α-hemolysin hla, while upregulating spa, a gene encoding a surface adhesin. Deletion of an Adh2 region encompassing the conserved CDFIM motif abolished this regulatory effect, indicating that this region is required for Adh2 activity. RNA-Seq analysis revealed global transcriptional reprogramming, with downregulation of virulence and metabolic genes. Proteomic profiling corroborated these findings, showing reduced abundance of proteins involved in metabolic pathways (e.g. carbohydrate, lipid, and nucleotide metabolism), consistent with a shift toward a low-energy, colonization-oriented state. Importantly, Adh2 did not impair S. aureus growth across a wide concentration range (0.01–10 g/L) but significantly enhanced biofilm formation. In vivo, Adh2 administration significantly improved survival in zebrafish embryos infected with S. aureus, validating its anti-virulence potential. Together, these findings demonstrate that Adh2 suppresses Agr signaling and virulence gene expression while promoting a persistent phenotype. By shifting S. aureus toward a metabolically reduced and less pathogenic state, Adh2 emerges as a promising candidate for therapeutic modulation of bacterial behavior, particularly in the context of chronic wound infections.
These findings indicated that PABA could be a candidate inhibitor of anthranilic acid signaling to interfere with the QS systems of R. solanacearum to attenuate the virulence and presented a non-antibiotic-based treatment strategy and provided a theoretical basis for the development of novel antibacterial treatment.
Chuanwang Yao, Wanlian Zhang, Zizi Lin et al.· Virulence· 0 citations
Aspartic proteases (APs) and G-protein-coupled receptors (GPCRs) are widespread in eukaryotes and play important roles in various cellular processes, including protein modification and cell signaling. In oomycetes, these two functional protein domains are combined into a single protein, forming a so-called bigram. However, the function of these AP-GPCR bigrams remains largely unknown. This study focuses on an AP-GPCR bigram in the devastating oomycete plant pathogen Phytophthora capsici, which is encoded by a single copy gene. Bioinformatic analyses confirmed that PcAPG encodes a membrane-associated protein with an N-terminal signal peptide, a central AP domain, and a C-terminal seven-transmembrane GPCR domain. Expression profiling revealed that PcAPG is constitutively expressed, with a significant upregulation during early host infection (1.5—12 hpi). Knocking out PcAPG using a modified CRISPR/Cas9 system resulted in mutants with only minor mycelial growth defects but severely attenuated virulence, indicating a crucial role for PcAPG in plant-pathogen interaction. Comparative transcriptomic analysis between the wild-type strain and a representative mutant suggests that PcAPG participates in regulating the expression of a suite of putative infection-related genes, potentially via a GPCR-mediated signaling pathway. Notably, in the wild-type strain, 158 genes involved in catabolic processes, such as polysaccharide degradation and hydrolase activities (e.g., alpha-galactosidase activity and arabinan catabolic process), were upregulated during infection, whereas in the mutant, these genes were not upregulated. Based on our findings it is concluded that the AP-GPCR bigram PcAPG is a key virulence factor in P. capsici with a putative role in downstream transcriptional activation of multiple catabolic enzymes thereby facilitating host colonization and invasion. This work unveils an AP-GPCR bigram as a unique signaling module in oomycete pathogens and identifies PcAPG as a promising potential target for novel management strategies against Phytophthora induced diseases.
Yanjing Yin, Lihong Li, Haidong Wang et al.· Phytopathology Research· 0 citations
How nutrient stress shapes bacterial evolution and the associated fitness trade-offs remains a central question in microbiology. Using Burkholderia thailandensis as a surrogate for the pathogen B. pseudomallei, we performed adaptive laboratory evolution with casein as the sole carbon source. Over 30 days of serial passaging, the population shifted towards protease deficiency, with mutants constituting 54.94% by the endpoint. These evolved strains exhibited pleiotropic virulence attenuation-including reduced rhamnolipid production, motility, auto-aggregation, and biofilm formation-alongside increased susceptibility to imipenem and chloramphenicol. RNA-seq analysis of evolved strain E3101 revealed 2,836 differentially expressed genes, with significant downregulation of quorum sensing (AHL synthesis), rhamnosyltransferases, flagellar assembly, and biofilm regulatory pathways. Our findings demonstrate that casein-driven evolution selects for social 'cheaters' that conserve energy by downregulating costly virulence determinants, revealing a fundamental virulence-fitness trade-off. The coordinated transcriptional repression of biofilm and antibiotic resistance pathways provides a mechanistic framework for understanding bacterial adaptation strategies and potential therapeutic vulnerabilities in Burkholderia.
Streptococcus agalactiae, also known as group B Streptococcus (GBS), is a major pathogen causing substantial economic losses in global tilapia aquaculture. The type VII secretion system (T7SS), present in Actinobacteria and Firmicutes, secretes effector proteins implicated in bacterial virulence, yet its functional mechanisms remain poorly defined. Here, we constructed an essC deletion mutant (∆essC) in S. agalactiae strain HN016 to investigate the role of T7SS in virulence. The ∆essC exhibited impaired growth and declined intracellular magnesium ion concentration in THB or magnesium-limited chemically defined medium (1 mM Mg2+-CDM); these defects were complemented by addition of wild-type culture supernatant. Transcriptomic and quantitative reverse transcription polymerase chain reaction (qRT–PCR) analyses revealed altered sugar metabolism and significant downregulation of capsule biosynthesis genes (cpsA, cpsB, and cpsD) in ∆essC. Consistent with this, the mutant produced markedly less capsular polysaccharide and displayed impaired capsule integrity. Furthermore, cellular assays confirmed that compared with HN016, the ∆essC mutant exhibited significantly reduced adhesion capacity, immune evasion ability, and cytotoxicity. More importantly, the ∆essC mutant showed attenuated virulence in vivo, with reduced bacterial loads in host tissues and diminished ability to cross the blood–brain barrier (BBB). Our findings provide the first evidence that the T7SS influences magnesium homeostasis and is essential for maintaining capsule integrity, both of which contribute critically to pathogenicity. This study identifies T7SS as a potential target for novel therapeutic strategies against streptococcal disease in aquaculture.
Fengyan Li, Chen Xu, Weiyi Ma et al.· Veterinary Research· 0 citations
Bacterial toxin-antitoxin (TA) systems are widespread genetic modules that regulate bacterial stress adaptation and pathogenicity. The atypical Type II psyrTA system encodes the toxin PsyrT with conserved RecQ-containing DEXDc and HELICc helicase domains, a rare architecture among characterized TA toxins. The toxic and pathogenic regulatory functions of helicase-containing TA toxins remain experimentally unvalidated. Here, we functionally characterized the psyrTA system in Pseudomonas plecoglossicida PQLYC4, the pathogen causing visceral white spot disease in large yellow croaker. Heterologous expression in Escherichia coli verified that PsyrT exerts potent growth-inhibitory toxicity, which is efficiently alleviated by cognate PsyrA via direct physical interaction. Deletion of psyrT markedly impaired biofilm formation, downregulated virulence gene transcription, reduced splenic colonization, and alleviated splenic histopathological damage in infected fish. Additionally, ΔpsyrT infection significantly attenuated host splenic cytokine transcriptional responses. Collectively, this study identifies PsyrT as a novel RecQ helicase domain-containing TA toxin and an important virulence modulator in P. plecoglossicida, expanding the functional diversity of bacterial TA systems.
Yudong Zheng, Jia-Tong Chen, Yan Teng et al.· Fish and Shellfish Immunolog...· 0 citations
