Search Results (102)

Enteritis is a common and recurrent disease in shrimp aquaculture, causing significant economic losses and management challenges. However, its specific causative pathogen remains unclear. Here, a pathogen strain, Vibrio parahaemolyticus VSP1, was directly isolated from shrimp with enteritis, and its pathogenicity and genomic characteristics were analyzed. Diseased shrimp exhibited lethargy, empty gut, hepatopancreatic atrophy, and severe intestinal damage. The gut bacterial community of diseased shrimp differed significantly from healthy shrimp (PERMANOVA, p < 0.05), with a 129% increase in Vibrio relative abundance. Nine Vibrio operational taxonomic units (OTUs) were enriched in diseased shrimp, and the dominant OTU1 shared 100% 16S rRNA identity with VSP1. VSP1 grew rapidly, utilized diverse carbon sources, and induced enteritis symptoms in over 90% of challenged shrimp. Genome analysis revealed 98.34% average nucleotide identity with V. parahaemolyticus ATCC 17802 and identified 156 putative virulence-related genes, mainly related to adherence, motility, and secretion systems. Unlike the strain ATCC 17802, VSP1 lacks thermostable direct hemolysin (TDH) and type III secretion system 2 (T3SS2), but contains alternative virulence factors such as Yersinia-like type IV pili and lipooligosaccharides, suggesting a distinct virulence strategy. This study identifies the pathogen responsible for shrimp enteritis and provides a foundation for targeted control strategies in aquaculture. Full article

Pseudomonas aeruginosa is a versatile Gram-negative pathogen that causes various infections in humans. The bacterium possesses a type III secretion system (T3SS) to deliver cytotoxic effector proteins into host cells, which plays an important role in bacterial pathogenesis. The T3SS is regulated by the master regulator ExsA, whose expression is controlled by multiple pathways. Here, we demonstrate that the catabolite repression control protein Crc controls T3SS activity by modulating exsA expression. We find that mutation of crc reduces the intracellular cAMP level by 1.76-fold under T3SS-inducing conditions, leading to approximately 2-fold reduction of the exsA expression. Further investigation reveals that Crc affects the mRNA stability of cyaB, which encodes an adenylate cyclase involved in cAMP synthesis. The cyaB 5′-UTR is identified as a key region through which Crc affects its mRNA stability. Our study elucidates a novel regulatory mechanism by which Crc controls the T3SS through modulating cyaB mRNA stability and subsequent cAMP synthesis under T3SS-inducing conditions. Full article

Salmonella Typhimurium, a significant intracellular foodborne pathogen, regulates host cell autophagy to achieve its own survival by injecting effector proteins into host cells via its type III secretion system (T3SS). Berberine hydrochloride (BH), an isoquinoline alkaloid derived from medicinal plants such as Coptis chinensis, has demonstrated potential antibacterial and immunomodulatory properties. However, the mechanisms by which BH combats S. Typhimurium by enhancing host autophagic flux through the inhibition of the type III secretion system remain to be fully elucidated. Here, we found that BH disrupts biofilm formation of S. Typhimurium, significantly inhibits the expression of genes associated with T3SS, and robustly enhances autophagy activity in macrophages infected with the pathogen. In a mouse model (C57BL/6 female 20 ± 1 g/mouse), BH significantly improved survival rates, reduced bacterial loads in tissues, and alleviated pathological damage. Molecular docking studies revealed that BH binds to key T3SS proteins, including SipB, SseA, and SsrB. These findings indicate that BH holds promise as a potentially effective therapeutic strategy for combating S. Typhimurium infections. Full article

Enteropathogenic Escherichia coli (EPEC) is a significant diarrheagenic pathotype responsible for severe gastrointestinal infections, particularly in vulnerable populations. The aim of this study is to utilize genome-based in silico analysis to study the structural and functional characteristics of the Type III Secretion System (T3SS) and its core effector proteins in EPEC strains. Representative proteins were selected, with particular interest placed on EscV and EscD as major parts of the export apparatus and the basal body, while the EspA effector protein forms the filamentous structure. Several in silico-based techniques were employed, revealing key structural proteins, core effectors, and adhesion-related proteins among the sequenced isolates. Of the 27 isolates analyzed, only 3 (11%) were found to carry LEE-encoded proteins associated with T3SS structural components (escV, escN, escD, and escU) and core effector proteins (espA, espD, espG, and eae). Structural predictions and Ramachandran plot validations suggested stability and potential functional conservation of T3SS proteins, with EscV and EspA selected for detailed 3D structural modelling. Insights into transmembrane domains, protein–protein interaction, and secondary structures were obtained, providing a comprehensive understanding of T3SS assembly and function. These findings suggest that the T3SS in EPEC consists of stable proteins that enable the system to remain functional. The structural and functional properties of the LEE genes encoding the T3SS in the EPEC pathotype represent promising targets for developing virulence blockers to disrupt the pathogenesis of a broad range of bacteria. This study is the first to report EPEC strains with functional T3SS in South Africa, emphasizing the importance of continued surveillance and molecular characterization of EPEC strains. The findings contribute to the development of targeted interventions to mitigate foodborne infections and improve public health. Full article

Furunculosis caused by Aeromonas salmonicida is one of the most common diseases in aquaculture, leading to significant economic losses. This study comprehensively investigated the dynamics of pathophysiological and histopathological disorders in rainbow trout (Oncorhynchus mykiss) infected with the moderately virulent strain A. salmonicida SL0n. Whole-genome analysis showed that strain SL0n belongs to the A. salmonicida species complex, possessing a single circular chromosome. The genome encodes a wide range of virulence factors, including adhesion systems (type IV pili, fimbriae), toxins (aerolysin, hemolysins), and a type II secretion system (T2SS), but notably lacks plasmids and a type III secretion system (T3SS). This genomic profile likely dictates a pathogenic mechanism reliant on secreted exotoxins (via T2SS), explaining the observed systemic cytotoxic damage. In an acute experiment, the 4-day LD₅₀ was determined to be 1.63 × 10⁶ CFU/fish. In a prolonged experiment, fish were injected with a sublethal dose (1.22 × 10⁶ CFU/fish—75% of LD50). The disease progressed through three consecutive stages. The early stage (1–2 DPI) was characterized by maximal bacterial load and activation of nonspecific immunity. The acute stage (4 DPI) manifested as severe septicemia and anemia, associated with systemic organ damage, which correlated with peak AST and ALT enzyme activity. The recovery stage (6 DPI) was marked by partial regression of inflammation, key biochemical and histological parameters indicated persistent liver and kidney dysfunction, signifying an incomplete recovery. These results demonstrate the pathogenesis of acute furunculosis and reveal that the genomic profile of the SL0n strain causes a sequential, systemic infection characterized by severe organ dysfunction. Full article

Mixed infections of Mannheimia haemolytica and Mycoplasma bovis are relatively common in bovine respiratory diseases, presenting severe respiratory symptoms and high mortality that severely endanger the cattle industry. In this study, a serotype A1 strain of Mannheimia haemolytica, designated as XJCJMh1, was isolated and identified from the lung tissue of a hybrid Simmental calf infected with Mycoplasma bovis. The pathogenicity of this strain was evaluated using Kunming mice as a model. The results indicated that infection with XJCJMh1 caused pathological manifestations such as pulmonary hemorrhage and edema in mice. Subsequently, the genome of this strain was sequenced and assembled using Illumina sequencing to obtain general genomic features. The genome was annotated and analyzed for gene functions using the Swiss-Prot, NR, GO, COG, KEGG, CAZy, TCDB, and Pfam databases. Additionally, the virulence factors and resistance genes of this strain were annotated using the PHI, VFDB, and CARD databases. The genome of Mannheimia haemolytica XJCJMh1 is 2,595,489 base pairs (bp) in length, with a GC content of 40.93%. Notably, this strain exhibits three distinct genomic islands and contains 98 effectors associated with the type III secretion system (T3SS). The XJCJMh1 strain harbors 74 virulence genes and 45 resistance genes. We annotated the proteins, genes, and associated GO and KEGG pathways of the XJCJMh1 strain; exploring the relationship between these annotations and the strain’s pathogenicity is of considerable value. This study is of great significance for clarifying the pathogenic mechanism and genetic characteristics of the Mannheimia haemolytica strain XJCJMh1 in cattle, and its results provide a scientific reference for analyzing the genomic basis of pathogenicity and drug resistance of Mannheimia haemolytica under co-infection conditions. Full article

Background/Objectives: Selective inhibition of bacterial virulence factors is a promising strategy to convert pathogenic bacteria into non-pathogenic commensals, circumventing the challenge of antibiotic resistance. This approach enables the host immune system to eliminate virulence-attenuated pathogens. Methods: In this study, we evaluated the effects of Lindera obtusiloba Blume extract and cinnamtannin B1, the active component of the ethyl acetate fraction, on the type III secretion system (T3SS) of Yersinia enterocolitica. Results: The ethyl acetate fraction, at 100 mg/L, effectively suppressed all three T3SS components—the flagellar, Ysa, and Ysc T3SSs. Cinnamtannin B1, isolated from the ethyl acetate fraction through separation and identified through nuclear magnetic resonance spectrometer analysis, significantly inhibited flagellar and Ysa T3SS secretion, while selectively inhibiting expression of key effector proteins YopH and YopO in the Ysc T3SS. Additionally, cinnamtannin B1 reduced Y. enterocolitica-induced RAW 264.7 macrophage mortality and prevented poly (ADP-ribose) polymerase degradation, a marker of apoptosis. Conclusions: These findings suggest cinnamtannin B1 from L. obtusiloba as a selective T3SS-targeting compound with mechanistic potential for anti-virulence intervention. Further in vivo validation will be necessary to evaluate its therapeutic applicability. Full article

Background/Objectives: Fluorothiazinone (FT), a small molecule of the 2,4-disubstituted-4H-[1,3,4]-thiadiazine-5-one class, is known to inhibit the type III secretion system (T3SS) in Gram-negative bacteria and has shown therapeutic potential in animal models and clinical trials. Given the evolutionary relationship between the T3SS and the bacterial flagellar apparatus, this study aimed to investigate the effects of FT on bacterial motility and flagellum assembly. Methods: Motility was assessed in Pseudomonas aeruginosa, Proteus mirabilis, pathogenic Escherichia coli, and Listeria monocytogenes using a semisolid agar assay and a microfluidic motility system. The mechanism of FT’s action was further examined through time-course analysis, Western blotting of surface flagella proteins, and transmission electron microscopy (TEM). Results: FT inhibited motility of P. aeruginosa, P. mirabilis, and E. coli in a dose-dependent manner, while L. monocytogenes motility remained unaffected. The inhibitory effect was not immediate but delayed 2–3 h post FT addition. Western blotting revealed the absence of surface flagella in EHEC grown with FT, and TEM confirmed structural disruption of flagella in P. mirabilis. Conclusions: FT selectively inhibits flagellum-based motility in Gram-negative bacteria. Obtained data suggested FT interference with flagellum biosynthesis rather than disruption of rotation. Motility inhibition can contribute to FT therapeutic effects on Gram-negative bacterial infections. Full article

The increasing demand for sustainable agricultural practises has sparked interest in microbes that promote plant immunity. Among these, Pseudomonas species have shown the potential to enhance induced systemic resistance (ISR) in crops. While type III secretion systems (T3SSs) in pathogenic bacteria have been widely studied for their role in local immunosuppression, their function in beneficial Pseudomonas species and on a systemic level remains largely unexplored. We show for the first time that the T3SS of a plant-beneficial Pseudomonas strain induces ISR by root colonisation. T3SS-positive Pseudomonas isolates were applied to the roots of sugar beet (Beta vulgaris L.) and systemic effects on plant immunity were assessed in leaves exposed to the pathogen P. syringae pv. aptata P21. Our results show that P. marginalis ORh26 reduced lesion size and pathogen proliferation in sugar beet leaves. ORh26 activated peroxidase and phenylalanine ammonia-lyase and upregulated NPR1 and MYC2 defence genes. Remarkably, a T3SS-deficient mutant of ORh26 failed to induce these effects. Genomic analysis identified T3SS structural genes and effector proteins, including a pectate lyase and an effector of the HopJ family, that may mediate these responses. This study reveals a previously uncharacterised role of T3SS in the induction of ISR and improves our understanding of plant–microbe interactions. Full article

Mango is a vital fruit crop in tropical and subtropical regions, yet pests and diseases cause 30–70% production losses. Developing disease-resistant cultivars through transgenic methods could mitigate these issues. Agrobacterium-mediated callus transformation is a common genetic engineering approach, but successful transgenic mango plants from callus remain unreported due to severe browning and necrosis post-infection. We hypothesized that Agrobacterium-induced immune responses trigger callus death, hindering transformation. To improve efficiency, we engineered an Agrobacterium strain carrying the type III secretion system (T3SS) and effector gene AvrPto. Compared to controls, infected calluses exhibited elevated reactive oxygen species (ROS), along with up-regulated ROS-related, gallic acid biosynthesis, and defense genes. Calluses infected with T3SS-AvrPto-harboring Agrobacterium showed delayed browning and necrosis versus those infected with the empty vector (NV). The transformation rate with Agrobacterium (T3SS-AvrPto-EGFP) reached 1.6%, while Agrobacterium (NV-EGFP) failed entirely. These findings demonstrate that T3SS and AvrPto enhance mango transformation efficiency, offering a promising strategy for breeding multi-resistant varieties. Full article

Vibrio parahaemolyticus is the leading cause of seafood-borne gastroenteritis. While its interaction with edible marine animals is well known, its impact on non-edible hosts remains under-explored. Using the sea anemone Exaiptasia pallida, we investigated Vibrio parahaemolyticus pathogenicity and the role of the Type III Secretion System (T3SS). In vivo infections with a 10⁷ CFU/mL inoculum of V. parahaemolyticus induced a 50% mortality rate after 7 days (LC50). Using isogenic mutant strains of V. parahaemolyticus with impaired key regulatory components of T3SS, impT3SS1 (CAB2), and impT3SS2 (CAB3), we demonstrated that disruption of T3SS1 significantly reduced anemone mortality. Next, we observed a time-dependent downregulation of T3SS1 effectors (VPA0450, VopQ, VopS) after 3 h and 6 h in the presence of the sea anemone, contrasting with the T3SS2-dependent VopC increased expression after 6 h. Further results support the capacity of V. parahaemolyticus to sense host-derived chemical cues and adjust its virulence strategies accordingly. Collectively, our findings broaden the understanding of V. parahaemolyticus O3:K6 as a pathogen for cnidarians and provide evidence of a major role for the T3SS1 effectors in this emerging model of host–pathogen interactions. Full article

Pseudomonas aeruginosa is a multi-drug-resistant opportunistic pathogen that adapts to challenging environments by deploying virulence factors, including the type III secretion system (T3SS). Emerging evidence points to a role for NADH dehydrogenase complexes in regulating virulence; however, their precise contributions remain unclear. Here, we identify PA2649, a component of the NADH dehydrogenase complex I (nuo operon), as a key regulator of T3SS-related activities. PA2649 deletion resulted in a twofold increase in exoS expression and enhanced cytotoxicity in both A549 cell and Chinese cabbage models. Full revertant of the nuo operon was necessary to restore exoS expression to wild-type levels, suggesting a critical connection between NADH dehydrogenase activity and T3SS regulation. The PA2649 mutation also disrupted the Rsm-Exs regulatory axis, downregulating gacS, rsmY, rsmZ, and hfq while upregulating exsC. Overexpression of rsmY, rsmZ, gacA, hfq, and exsD partially rescued T3SS function, confirming that PA2649 influences T3SS via the Rsm-Exs pathway. Furthermore, PA2649 deletion altered motility, biofilm formation, pyocyanin production, protease activity, and antibiotic susceptibility. These phenotypes could not be complemented with T3SS regulatory genes alone, indicating that PA2649 modulates these traits through mechanisms independent of the Rsm-Exs axis, potentially involving NADH dehydrogenase-associated pathways. This study underscores the multifaceted role of PA2649 in regulating P. aeruginosa pathogenicity and resistance, providing novel insights into its complex regulatory networks and highlighting new avenues for therapeutic targeting. Full article

The expression of the rhizobial symbiotic genes is controlled by various transcriptional regulators. After induction with appropriate plant flavonoids, NodD is responsible for the activation of the expression of genes related to Nod factor synthesis and secretion, but also, in most rhizobia harbouring a symbiotic type III secretion system (T3SS), the expression of ttsI. The ttsI gene encodes the positive regulator of the expression of T3SS-related genes, including those coding for structural components and for type III-secreted effector proteins. However, besides this general role among T3SS-harbouring rhizobia, different works have shown additional functions of TtsI in the regulation (positive or negative) of other bacterial traits such as the production of modified lipopolysaccharides or different types of motility (swimming or surface spreading). Interestingly, these additional functions appear to be rather specific than general among rhizobia. Moreover, in Sinorhizobium fredii HH103, TtsI affects the expression of various genes belonging to the nod regulon, including several transcriptional regulators. This review summarizes all the well-known bacterial traits affected by TtsI and describes other rhizobial genes that are regulated by TtsI but whose function remains to be established. Full article

The type III secretion system (T3SS) is a nano-machine that allows Gram-negative bacteria to alter eukaryotic host biology by directly delivering effector proteins from the bacterial cytoplasm. Protein delivery based on the bacterial T3SS has been widely used in research in biology. This review explores recent advancements in the structure and function of the T3SS. We explore the molecular underpinnings of the T3SS apparatus, which spans bacterial and host cell membranes, and discuss the intricate transport mechanisms of effector proteins. Furthermore, this review emphasizes the innovative applications of the T3SS in crop biology, where it has been leveraged to study plant–pathogen interactions. By summarizing the current knowledge and recent progress, we underscore the potential of the T3SS as a powerful tool in biological sciences and their implications for future research in plant pathology and agricultural biotechnology. Full article

The Chlamydiaceae are a family of obligate intracellular bacteria known for their unique biphasic developmental cycle. Chlamydial are associated with various host organisms, including humans, and have been proposed as emerging pathogens. Genomic studies have significantly enhanced our understanding of chlamydial biology, host adaptation, and evolutionary processes. In this study, we conducted a complete pangenome association analysis (pan-GWAS) using 101 genomes from the Chlamydiaceae family to identify differentially represented genes in Chlamydia and Chlamydophila, revealing their distinct evolutionary strategies for interacting with eukaryotic hosts. Our analysis identified 289 genes with differential abundance between the two clades: 129 showed a strong association with Chlamydia and 160 with Chlamydophila. Most genes in Chlamydia were related to the type III secretion system, while Chlamydophila genes corresponded to various functional categories, including translation, replication, transport, and metabolism. These findings suggest that Chlamydia has developed a high dependence on mammalian cells for replication, facilitated by a complex T3SS for intracellular manipulation. In contrast, the metabolic and functional diversity in Chlamydophila allows it to colonize a broad range of hosts, such as birds, reptiles, amphibians, and mammals, making it a less specialized clade. Full article