The Edwardsiella piscicida Type III Translocon Protein EseC Inhibits Biofilm Formation by Sequestering EseE

Exploring the Proteomic Landscape and Immunomodulatory Functions of Edwardsiella piscicida Derived Extracellular Vesicles

Extracellular vesicles (EVs) have garnered attention in research for their potential as biochemical transporters and immune modulators, crucial for regulating the host immune system. The present study was conducted to isolate and characterize EVs from Gram negative bacteria Edwardsiella piscicida (EpEVs) and investigate their proteomic profile and immune responses. Isolation of EpEVs was carried out using ultracentrifugation method. Transmission electron microscopy results confirmed the spherical shape of EpEVs. The average size and zeta potential were 85.3 ± 1.8 nm and -8.28 ± 0.41 mV, respectively. EpEVs consisted of 1,487 distinct proteins. Subcellular localization analysis revealed that "cell" and "cell part" were the most predominant areas for protein localization. Proteins associated with virulence, along with several chaperones that facilitate protein folding and stability, were also present. No toxicity was detected when EpEVs were treated to fathead minnow (FHM) cells up to 100 μg/ml. Fluorescent-labeled EpEVs showed cellular internalization in FHM cells at 24 h post treatment (hpt). In-vitro gene expression in Raw 264.7 cells showed upregulation of interleukin (Il)6, Il1β, and interferon (Ifn)β with simultaneous upregulation of anti-inflammatory Il10. In vivo, gene expression revealed that except for heat shock protein (hsp)70, all other genes were upregulated suggesting that EpEVs induced the expression of immune-related genes. Western blot analysis showed increased protein levels of tumor necrosis factor (Tnf)α in EpEVs-treated spleen tissue of zebrafish. Our results confirm that EpEVs can be successfully isolated using the ultracentrifugation method. Furthermore, exploring immunomodulatory mechanism of EpEVs is essential for their potential use as novel therapeutics in fish medicine.

Proteus faecis: a potentially pathogenic bacterium isolated from the freshwater Yangtze finless porpoise

Proteus faecis is a gram-negative facultative anaerobic rod-shaped bacterium capable of swarming motility. It has been isolated from numerous sources such as humans, animals, and refuse and is considered potentially pathogenic towards humans. In this study, bacteria were isolated from the blowhole of a Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis; YFP) living in captivity in China. One bacterium, P. faecis porpoise, was isolated and whole genome sequencing done. Biofilm formation, motility and antimicrobial resistance were also investigated. To find putative virulence factors, the genome of P. faecis strain porpoise was compared to the genomic sequences of eight other P. faecis isolates using the Bacterial and Viral Bioinformatics Resource Center (BV-BRC) ( https://www.bv-brc.org/ ). The goal of this study was to initially characterize the pathogenicity of this bacterium isolated from a cetacean species using both pathogenomics and conventional approaches.

Edwardsiella tarda Attenuates Virulence upon Oxytetracycline Resistance

The relationship between antibiotic resistance and bacterial virulence has not yet been fully explored. Here, we use Edwardsiella tarda as the research model to investigate the proteomic change upon oxytetracycline resistance (LTB4-ROTC). Compared to oxytetracycline-sensitive E. tarda (LTB4-S), LTB4-ROTC has 234 differentially expressed proteins, of which the abundance of 84 proteins is downregulated and 15 proteins are enriched to the Type III secretion system, Type VI secretion system, and flagellum pathways. Functional analysis confirms virulent phenotypes, including autoaggregation, biofilm formation, hemolysis, swimming, and swarming, are impaired in LTB4-ROTC. Furthermore, the in vivo bacterial challenge in both tilapia and zebrafish infection models suggests that the virulence of LTB4-ROTC is attenuated. Analysis of immune gene expression shows that LTB4-ROTC induces a stronger immune response in the spleen but a weaker response in the head kidney than that induced by LTB4-S, suggesting it's a potential vaccine candidate. Zebrafish and tilapia were challenged with a sublethal dose of LTB4-ROTC as a live vaccine followed by LTB4-S challenge. The relative percentage of survival of zebrafish is 60% and that of tilapia is 75% after vaccination. Thus, our study suggests that bacteria that acquire antibiotic resistance may attenuate virulence, which can be explored as a potential live vaccine to tackle bacterial infection in aquaculture.

Screening and identification of functional bacterial attachment genes in aerobic granular sludge

The screening and identification of attachment genes is important to exploring the formation mechanism of biofilms at the gene level. It is helpful to the development of key culture technologies for aerobic granular sludge (AGS). In this study, genome-wide sequencing and gene editing were employed for the first time to investigate the effects and functions of attachment genes in AGS. With the help of whole-genome analysis, ten attachment genes were screened from thirteen genes, and the efficiency of gene screening was greatly improved. Then, two attachment genes were selected as examples to further confirm the gene functions by constructing gene-knockout recombinant mutants of Stenotrophomonas maltophilia; when the two attachment genes were knocked out, the attachment potential was reduced by 50.67% and 43.93%, respectively. The results provide a new theoretical principle and efficient method for the development of AGS from the perspective of attachment genes.

Bacteria autoaggregation: how and why bacteria stick together

Autoaggregation, adherence between identical bacterial cells, is important for colonization, kin and kind recognition, and survival of bacteria. It is directly mediated by specific interactions between proteins or organelles on the surfaces of interacting cells or indirectly by the presence of secreted macromolecules such as eDNA and exopolysaccharides. Some autoaggregation effectors are self-associating and present interesting paradigms for protein interaction. Autoaggregation can be beneficial or deleterious at specific times and niches. It is, therefore, typically regulated through transcriptional or post-transcriptional mechanisms or epigenetically by phase variation. Autoaggregation can contribute to bacterial adherence, biofilm formation or other higher-level functions. However, autoaggregation is only required for these phenotypes in some bacteria. Thus, autoaggregation should be detected, studied and measured independently using both qualitative and quantitative in vitro and ex vivo methods. If better understood, autoaggregation holds the potential for the discovery of new therapeutic targets that could be cost-effectively exploited.

An Edwardsiella piscicida esaS mutant reveals contribution to virulence and vaccine potential

Edwardsiella piscicida is a Gram-negative pathogen that causes disease in diverse aquatic organisms. The disease leads to extensive losses in commercial aquaculture species, including farmed U.S. catfish. The type III secretion system (T3SS) often contributes to virulence of Gram-negative bacteria. The E. piscicida esaS gene encodes a predicted T3SS export apparatus protein. In the current study, an E. piscicida esaS mutant was constructed and characterized to increase our understanding of the role of T3SS in E. piscicida virulence. Deletion of esaS did not significantly affect biofilm formation and hemolytic activity of E. piscicida, but it had significant effects on expression of hemolysis and T3SS effector genes during biofilm growth. EpΔesaS showed significantly (P < 0.05) reduced virulence in catfish compared to the parent strain. No mortalities occurred in fish infected with EpΔesaS at 6.3 × 10⁵ and 1.26 × 10⁶ CFU/fish compared to 26% mortality in fish infected with wild-type E. piscicida at 7.5 × 10⁵ CFU/fish. Bioluminescence imaging indicated that EpΔesaS invades catfish and colonizes for a short period in the organs. Furthermore, catfish immunized with EpΔesaS at 6.3 × 10⁵ and 1.26 × 10⁶ CFU provided 47% and 87% relative percent survival, respectively. These findings demonstrated that esaS plays a role in E. piscicida virulence, and the deletion mutant has vaccine potential for protection against wild-type E. piscicida infection.

HutZ is required for biofilm formation and contributes to the pathogenicity of Edwardsiella piscicida

Edwardsiella piscicida is a severe fish pathogen. Haem utilization systems play an important role in bacterial adversity adaptation and pathogenicity. In this study, a speculative haem utilization protein, HutZ_Ep, was characterized in E. piscicida. hutZ_Ep is encoded with two other genes, hutW and hutX, in an operon that is similar to the haem utilization operon hutWXZ identified in V. cholerae. However, protein activity analysis showed that HutZ_Ep is probably not related to hemin utilization. To explore the biological role of HutZ_Ep, a markerless hutZ_Ep in-frame mutant strain, TX01ΔhutZ, was constructed. Deletion of hutZ_Ep did not significantly affect bacterial growth in normal medium, in iron-deficient conditions, or in the presence of haem but significantly retarded bacterial biofilm growth. The expression of known genes related to biofilm growth was not affected by hutZ_Ep deletion, which indicated that HutZ_Ep was probably a novel factor promoting biofilm formation in E. piscicida. Compared to the wild-type TX01, TX01ΔhutZ exhibited markedly compromised tolerance to acid stress and host serum stress. Pathogenicity analysis showed that inactivation of hutZ_Ep significantly impaired the ability of E. piscicida to invade and reproduce in host cells and to infect host tissue. In contrast to TX01, TX01ΔhutZ was defective in blocking host macrophage activation. The expression of hutZ_Ep was directly regulated by the ferric uptake regulator Fur. This study is the first functional characterization of HutZ in a fish pathogen, and these findings suggested that HutZ_Ep is essential for E. piscicida biofilm formation and contributes to host infection.

Putative virulence factors of Plesiomonas shigelloides

Plesiomonas shigelloides is a Gram-negative rod-shaped bacterium which has been isolated from humans, animals and the environment. It has been associated with diarrhoeal disease in humans and various epizootic diseases in animals. In this study P. shigelloides strains were isolated from the faecal material of a captive Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis; YFP) living in semi-natural conditions in China. Plesiomonas shigelloides strain EE2 was subjected to whole genome sequencing. The draft genome was then compared to the genome sequences of ten other P. shigelloides isolates using the Pathosystems Resource Integration Center pipeline. In addition to several virulence factors which have been previously reported, we are proposing new candidate virulence factors such as a repeats-in-toxin protein, lysophospholipase, a twin-arginine translocation system and the type VI secretion effector Phospholipase A1.