Complete genome analysis of a virulent Vibrio scophthalmi strain VSc190401 isolated from diseased marine fish half-smooth tongue sole, Cynoglossus semilaevis

The type II secretion system as an underappreciated and understudied mediator of interbacterial antagonism

Interbacterial antagonism involves all major phyla, occurs across the full range of ecological niches, and has great significance for the environment, clinical arena, and agricultural and industrial sectors. Though the earliest insight into interbacterial antagonism traces back to the discovery of antibiotics, a paradigm shift happened when it was learned that protein secretion systems (e.g., types VI and IV secretion systems) deliver toxic "effectors" against competitors. However, a link between interbacterial antagonism and the Gram-negative type II secretion system (T2SS), which exists in many pathogens and environmental species, is not evident in prior reviews on bacterial competition or T2SS function. A current examination of the literature revealed four examples of a T2SS or one of its known substrates having a bactericidal activity against a Gram-positive target or another Gram-negative. When further studied, the T2SS effectors proved to be peptidases that target the peptidoglycan of the competitor. There are also reports of various bacteriolytic enzymes occurring in the culture supernatants of some other Gram-negative species, and a link between these bactericidal activities and T2SS is suggested. Thus, a T2SS can be a mediator of interbacterial antagonism, and it is possible that many T2SSs have antibacterial outputs. Yet, at present, the T2SS remains relatively understudied for its role in interbacterial competition. Arguably, there is a need to analyze the T2SSs of a broader range of species for their role in interbacterial antagonism. Such investigation offers, among other things, a possible pathway toward developing new antimicrobials for treating disease.

Partial Characterization of Three Bacteriophages Isolated from Aquaculture Hatchery Water and Their Potential in the Biocontrol of Vibrio spp

Bacteriophages are currently considered one of the most promising alternatives to antibiotics under the 'One Health' approach due to their ability to effectively combat bacterial infections. This study aimed to characterize Vibrio species in hatchery water samples collected from an aquaculture farm and investigate the biocontrol potential of their bacteriophages. Vibrio spp. (n = 32) isolates confirmed by LNA probe-based qPCR were used as hosts. Three Vibrio phages were isolated. IKEM_vK exhibited a broad host range, infecting V. harveyi (n = 8), V. alginolyticus (n = 2), V. azureus (n = 1), and V. ordalii (n = 1). IKEM_v5 showed lytic activity against V. anguillarum (n = 4) and V. ordalii (n = 1), while IKEM_v14 was specific to V. scophtalmi (n = 4). The morphological appearance of phages and their lytic effects on the host were visualized using scanning electron microscopy (SEM). All three phages remained relatively stable within the pH range of 6-11 and up to 60 °C. The lytic activities and biofilm inhibition capabilities of these phages against planktonic Vibrio cells support their potential applications in controlling vibriosis in aquaculture systems.

Population response of intestinal microbiota to acute Vibrio alginolyticus infection in half-smooth tongue sole (Cynoglossus semilaevis)

Introduction

Vibriosis causes enormous economic losses of marine fish. The present study investigated the intestinal microbial response to acute infection of half-smooth tongue sole with different-dose Vibrio alginolyticus within 72 h by metagenomic sequencing.

Methods

The inoculation amount of V. alginolyticus for the control, low-dose, moderate-dose, and high-dose groups were 0, 8.5 × 101, 8.5 × 104, and 8.5 × 107 cells/g respectively, the infected fish were farmed in an automatic seawater circulation system under a relatively stable temperature, dissolved oxygen and photoperiod, and 3 ~ 6 intestinal samples per group with high-quality DNA assay were used for metagenomics analysis.

Results

The acute infections with V. alginolyticus at high, medium, and low doses caused the change of different-type leukocytes at 24 h, whereas the joint action of monocytes and neutrophils to cope with the pathogen infection only occurred in the high-dose group at 72 h. The metagenomic results suggest that a high-dose V. alginolyticus infection can significantly alter the intestinal microbiota, decrease the microbial α-diversity, and increase the bacteria from Vibrio and Shewanella, including various potential pathogens at 24 h. High-abundance species of potential pathogens such as V. harveyii, V. parahaemolyticus, V. cholerae, V. vulnificus, and V. scophthalmi exhibited significant positive correlations with V. alginolyticus. The function analysis revealed that the high-dose inflection group could increase the genes closely related to pathogen infection, involved in cell motility, cell wall/ membrane/envelope biogenesis, material transport and metabolism, and the pathways of quorum sensing, biofilm formation, flagellar assembly, bacterial chemotaxis, virulence factors and antibiotic resistances mainly from Vibrios within 72 h.

Discussion

It indicates that the half-smooth tongue sole is highly likely to be a secondary infection with intestinal potential pathogens, especially species from Vibrio and that the disease could become even more complicated because of the accumulation and transfer of antibiotic-resistance genes in intestinal bacteria during the process of V. alginolyticus intensified infection.

Determination of histopathological effects and myoglobin, periostin gene-protein expression levels in Danio rerio muscle tissue after acaricide yoksorrun-5EC (hexythiazox) application

Although pesticides are essential agrochemicals to annihilate harmful organisms in agriculture, their uncontrolled use has become an important threat to environmental health. Exposure to pesticides can affect many biological systems including immune system, endocrine system, and nervous system. However, the potential side effects of pesticides to skeletal muscle system remain unclear. Present study has focused on the evaluation of this issue by using an acaricide, yoksorrun-5EC (hexythiazox), in an aquatic model organism, Danio rerio. The histological analyses revealed that increased concentrations of the acaricide cause degradation of skeletal muscle along with increased necrosis and atrophy in myocytes, intercellular edema, and increased infiltrations between perimysium sheaths of muscle fibers. The effects of acaricide on myoglobin and periostin, which are associated with oxygen transport and muscle regeneration, respectively, were investigated at the gene and protein levels. RT-PCR results suggested that high concentration yoksorrun-5EC (hexythiazox) can induce myoglobin and periostin genes. Similar results were also obtained in the protein levels of these genes by western blotting analysis. These results suggested that yoksorrun-5EC (hexythiazox)-dependent disruption of skeletal muscle architecture is closely associated with the expression levels of myoglobin and periostin genes in Danio rerio model.

Dietary bile acid supplementation reveals beneficial effects on intestinal healthy status of tongue sole (Cynoglossus semiliaevis)

The aim of this study was to investigate the effects of dietary bile acids (BAs) on intestinal healthy status of tongue sole in terms of immunity, antioxidant status, digestive ability, mucosal barrier-related genes expression and microbiota. Three experimental diets were prepared with BA levels at 0 mg/kg (CT), 300 mg/kg (BA1) and 900 mg/kg (BA2) in a commercial basal diet. Each diet was fed to three replicates with 120 fish (10.87 ± 0.32 g) in each tank. After an 8-week feeding trial, growth parameters were significantly enhanced in both BAs supplementary groups (P < 0.05), and compared with CT group, survival rate in BA2 group was significantly improved (P < 0.05). Intestinal lysozyme activity and contents of immunoglobulin M and complement 3 were significantly increased in both BAs supplementary groups (P < 0.05), suggesting an enhancement effect on the non-specific immune response. BAs inclusion also significantly improved intestinal antioxidant capabilities by increasing antioxidase activities and decreasing malondialdehyde levels. In addition, compared with CT group, intestinal digestive ability was substantially enhanced as indicated by the significantly increased lipase activity in BA2 group (P < 0.05) and significantly increased amylase activity in BA1 and BA2 groups (P < 0.05). Coincidentally, BAs inclusion significantly upregulated the relative expression of intestinal mucosal barrier-related genes (P < 0.05). Further, dietary BAs distinctly remodeled intestinal microbiota by decreased the abundance of some potential pathogenic bacteria. In conclusion, dietary BAs supplementation is an effective way to improve the intestinal healthy status of tongue sole.

Alterations in gills and intestine of Danio rerio after exposure to acaricide yoksorrun-5EC (hexythiazox): histopathologic and morphometric evaluation

In this study, histopathological and morphological changes in gill and intestinal tissue of zebra fish exposed to acaricide yoksorrun were aimed to determine. Yoksorrun was applied to the experimental groups as 0.01 mL/L, 0.02 mL/L, and 0.03 mL/L. Histopathological findings which showed a parallel increase with the amount of exposure in the gill were determined. In the gills, disruption of lamellae shape, shortening and breakage of primary and secondary lamellae, edema, fusion, and separation in the secondary lamellae epithelium, hyperplasia were observed. In the intestine tissue of some groups, advanced necrosis at the tip of the villi and deterioration of the overall integrity of the villi in these regions, epithelial hyperplasia, increasing in eosinophilic cells in the submucosa, and dissolution in muscle fibers of tunica muscularis were observed. In the morphometric analysis of the gills, a significant decrease in gas exchange (PAGE) percentages (p < 0.0001) was observed in the experiment group compared to the control group. Compared to the control group, a significant decrease in the interlamellar distance and secondary lamellar length measurements of the gills and a significant increase in the secondary lamellar width measurement were observed. In basal epithelial thickness measurement, the result was insignificant between the groups. According to the results of the morphometric analysis of the intestine, a significant decrease in musculus externa was observed only in the group 2. In total wall thickness, there was a significant thinning (p < 0.0001) in all experimental groups. There was a significant shortening of the villi length (p < 0.0001) and a significant increase (p < 0.0001) in the villus width only in the group 2 and group 3. A significant increase in epithelial thickness after application was observed (p < 0.0001) in all groups compared to the control group. Based on the findings, it was decided that the living in the aquatic ecosystem would be adversely affected by this acaricide if exposed.