Jul 2026· Journal of food microbiology· Vol 461, pp.
111995
· 0 citations
Medicine
TL;DR
It is demonstrated that flgK is indispensable for flagellar assembly, motility, and virulence in V. mimicus, and that its loss induces broad physiological adaptations that impair food-related persistence and host colonization, identifying flgK as a potential target for aquatic food safety interventions.
Abstract
Vibrio mimicus is a foodborne pathogen that contaminates aquatic products and causes gastroenteritis in humans. The flagellar protein FlgK is required for flagellar assembly and motility in several bacteria, but its role in V. mimicus remains unclear. In this study, we constructed an in-frame flgK deletion mutant and a complementary strain to investigate the biological functions of FlgK. Transmission electron microscopy revealed a complete loss of flagellar structures in the ΔflgK strain, which was restored upon complementation. Loss of flgK exerted no significant impact on bacterial growth yet abolished swimming motility entirely and diminished biofilm formation capacity. The ΔflgK strain exhibited significantly decreased adhesion to prawn, crayfish, plastic, glass, and stainless steel compared to the WT strain. Consistently, flgK deletion reduced colonization and pathogenicity in the prawn host. Transcriptomic analysis revealed extensive downregulation of flagellar biogenesis pathways accompanied by coordinated alterations in genes involved in transport processes and central metabolism in the ΔflgK strain. Collectively, these results demonstrate that flgK is indispensable for flagellar assembly, motility, and virulence in V. mimicus, and that its loss induces broad physiological adaptations that impair food-related persistence and host colonization, identifying flgK as a potential target for aquatic food safety interventions.
Vibrio parahaemolyticus is a major seafood-borne pathogen whose ability to form biofilms enhances its persistence in food-processing environments and contributes to its resistance to antimicrobial agents. In this study, we investigated the role of the LysR-type transcriptional regulator LtrB (VPA0388) in coordinating the switch between motility and biofilm formation in V. parahaemolyticus. We demonstrated that LtrB is required for proper biofilm development, extracellular matrix production, and wrinkled colony morphotype formation, while simultaneously repressing both swimming and swarming motility. Mechanistically, we showed that LtrB acts as a direct transcriptional regulator that binds to the promoter regions of multiple genes, including biofilm-matrix genes (cpsA, scvE, cpsQ, mfpA) and flagellar genes (flgM, flgA, flgB, flgK, lafA, fliD), activating the former and repressing the latter. In contrast, the regulation of motY and fliM appears to be indirect, as no binding of LtrB to their promoter regions was detected. Furthermore, LtrB exerts these regulatory effects largely independently of the c-di-GMP signaling pathway, as intracellular c-di-GMP levels remain unaltered upon ltrB deletion. Consistent with its role in promoting a sessile lifestyle, LtrB was required for bacterial adhesion to biotic (mussel and shrimp) and abiotic (glass and stainless steel) surfaces relevant to food production. These findings establish LtrB as a regulator that promotes a sessile, biofilm-forming lifestyle by downregulating motility and upregulating matrix production, thereby facilitating persistent colonization in food-related environments.
Wenli Cai, Wu Xu, Yanyan Ding et al.· Current Research in Food Sci...· 0 citations
Salmonella typhimurium, a Gram-negative pathogen widely distributed in the environment, poses a serious threat to public health by contaminating food and causing foodborne diseases. Our preliminary study found that under thymol stress, the expression of YibT, a poorly characterized factor in salmonella, was significantly reduced, and deletion of the yibT gene markedly impaired biofilm formation. However, the biological role of yibT in salmonella pathogenesis remains unclear. In this study, the λ-Red homologous recombination system and pET28a vector were used to construct the single deletion mutant STΔrpoS, the double deletion mutant STΔrpoSΔyibT, complementation strains, and an overexpression strain. Promoter reporter vectors were constructed using pKP302. Growth characteristics, biofilm formation, adhesion, invasion, virulence, and pathogenicity were evaluated. The regulatory relationship between rpoS and yibT was examined by β-galactosidase assays. Results showed that deletion of rpoS and yibT led to slow growth, reduced biofilm formation, and decreased flagella and surface appendages under transmission electron microscopy. qRT-PCRshowed that there is a negative feedback loop between yibT and rpoS, where RpoS positively regulates yibT transcription and YibT negatively regulates RpoS expression. Preliminary detection of β-galactosidase confirms that yibT may be located downstream of rpoS. Cellular infection models demonstrated that deletion of yibT and rpoS significantly reduced salmonella adhesion, invasion, and intracellular survival. In mouse infection experiments, bacterial loads in the liver, spleen, and ileum were markedly decreased in mutant-infected mice, with further reduction under quercetin intervention. Flow cytometry analysis of T-cell subsets suggested attenuated immune modulation by the mutant strains, indicating reduced pathogenicity. Collectively, yibT contributes to regulate adhesion and invasion of S. typhimurium, and its deletion attenuates bacterial virulence and host pathogenicity. YibT may participate in the virulence regulatory network by interacting with the transcriptional regulator RpoS. This study provides a theoretical basis for elucidating the molecular mechanism by which YibT modulates salmonella pathogenicity.
Bingbing Wang, Min Yue, Jianjun Chen et al.· Microbial Pathogenesis· 0 citations
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
Pseudomonas plecoglossicida is a major etiological agent of visceral white-spot disease in diverse aquaculture species. Chorismate synthase (AroC), a key enzyme in the aromatic amino acid biosynthetic pathway, is essential for central metabolism and has been implicated in bacterial virulence. In this study, an aroC deletion mutant (ΔaroC) and a complemented strain (CΔaroC) were constructed to investigate the role of AroC in virulence regulation and to evaluate its potential as a live-attenuated vaccine candidate. Compared with the wild-type (WT) strain, ΔaroC exhibited significantly reduced growth, motility, hemolytic activity, and biofilm formation. In infection experiments, ΔaroC showed markedly attenuated virulence, resulting in 90% host survival. In a goldfish vaccination-challenge model, immunization with ΔaroC conferred moderate protective efficacy, with a relative percent survival (RPS) of 62%. Transcriptomic analysis revealed that aroC deletion led to the downregulation of genes involved in amino acid metabolism, ABC transporters, and quorum sensing pathways. These results suggest that AroC contributes to pathogenicity by coordinating metabolic processes and environmental adaptation. Together, our findings identify AroC as an important virulence determinant in P. plecoglossicida and suggest that ΔaroC is a promising live-attenuated vaccine candidate that warrants further validation in the natural host.
Yingchao Wang, Ping Shao, Zhijuan Mao et al.· Microbial Pathogenesis· 0 citations
Campylobacter jejuni is the leading cause of bacterial foodborne diarrheal disease worldwide. Despite its microaerophilic nature, C. jejuni is ubiquitous in aerobic environments and must possess specific adaptation mechanisms against oxidative stress. Here, we identified a novel role for FlhF, a GTPase essential for proper flagellar assembly, in promoting resistance to hydrogen peroxide (H2O2). Comparative transcriptomic analysis under H2O2 stress revealed that deletion of flhF leads to significant downregulation of oxidative stress-related genes. FlhF directly interacts with TonB2, an iron transport-associated protein, via its B and N domains. Codeletion of flhF and tonB2 leads to increased sensitivity to H2O2, suggesting a synergistic interaction. Moreover, the FlhF-TonB2 interaction promotes H2O2 detoxification, potentially by modulating intracellular iron homeostasis and influencing redox processes. Together, these findings reveal a novel function of FlhF in the oxidative stress response of C. jejuni, offering new insights into flagella-associated defense mechanisms in this pathogen.
Clostridioides difficile is a major cause of antibiotic-associated diarrhea and a significant public health threat. During its infectious cycle, C. difficile encounters various stresses within the gastrointestinal tract. Clp proteases play a crucial role in bacterial stress responses and protein homeostasis. In this study, we investigated the role of the Clp ATPase, ClpC, in C. difficile physiology using genetic, phenotypic, and proteomic analyses. Deletion of clpC reduced heat shock survival but did not affect growth or stationary phase survival under non-stress conditions. Comparative proteomics revealed that ClpC influences the abundance of proteins involved in sporulation, motility, metabolism, and cell wall biosynthesis. The ΔclpC mutant exhibited faster sporulation and increased motility compared to the parental strain. Peptidoglycan quantification showed a significant increase in the ΔclpC mutant, suggesting ClpC's involvement in cell wall homeostasis. The mutant also displayed altered sensitivity to cell wall-targeting antibiotics. Unlike in other bacteria, ClpC did not control the level of MurA, a key enzyme in peptidoglycan precursor synthesis. Instead, the SEDS protein RodA, a transglycosylase involved in peptidoglycan polymerization, accumulated in the ΔclpC mutant. Our findings highlight the pleiotropic role of ClpC in C. difficile, particularly in sporulation, motility, and cell wall metabolism, likely through the degradation of key proteins. Understanding the molecular mechanisms of ClpC-mediated proteolysis in C. difficile stress responses and virulence may provide insights for the development of novel strategies to combat this important pathogen.
Pierre Lacotte, Aurélie Lotoux, Kimberley Casado et al.· Microbial Pathogenesis· 0 citations
