Time-resolved RNA-seq provided a new understanding of intestinal immune response of European eel (Anguilla anguilla) following infection with Aeromonas hydrophila

Transcriptome analysis of host anti-Aeromonas hydrophila infection revealed the pathogenicity of A. hydrophila to American eels (Anguilla rostrata)

Aeromonas hydrophila is a commonly pathogenic bacterium in cultivated eels, but its pathogenicity to American eel (Anguilla rostrata) and the molecular mechanism of host anti-A. hydrophila infection remains uncertain. In this study, LD50 of A. hydrophila to American eels was determined and bacterial load in the liver and kidney of eels was assessed post 2.56 doses of LD50 of A. hydrophila infection. The results showed that the LD50 of A. hydrophila to American eels was determined to be 3.9 × 105 cfu/g body weight (7.8 × 106 cfu/fish), and the bacterial load peaked at 36 h post the infection (hpi) in the liver. Then, the histopathology was highlighted by congestion in splenic blood vessels, atrophied glomeruli, and necrotic hepatocytes. Additionally, the results of qRT-PCR revealed that 18 host immune-related genes showed significantly up or downregulated post-infection compare to that of pre-infection. Finally, results of the RNA-seq revealed 10 hub DEGs and 7 encoded proteins play essential role to the anti-A. hydrophila infection in American eels. Pathogenicity of A. hydrophila to American eels and RNA-seq of host anti-A. hydrophila infection were firstly reported in this study, shedding new light on our understanding of the A. hydrophila pathogenesis and the host immune response to the A. hydrophila infection strategies in gene transcript.

Transcriptome Analysis of Host Anti-Vibrio harveyi Infection Revealed the Pathogenicity of V. harveyi to American Eel (Anguilla rostrata)

Vibrio harveyi, a recently discovered pathogenic bacterium isolated from American eels (Anguilla rostrata), poses uncertainties regarding its pathogenesis in American eel and the molecular mechanisms underlying host defense against V. harveyi infection. This study aimed to determine the LD50 of V. harveyi in American eel and assess the bacterial load in the liver, spleen, and kidney post-infection with the LD50 dose. The results showed that the LD50 of V. harveyi via intraperitoneal injection in American eels over a 14d period was determined to be 1.24 × 103 cfu/g body weight (6.2 × 104 cfu/fish). The peak bacterial load occurred at 36 h post-infection (hpi) in all three organs examined. Histopathology analysis revealed hepatic vein congestion and thrombi, tubular vacuolar degeneration, and splenic bleeding. Moreover, quantitative reverse transcription polymerase chain reaction (qRT-PCR) results indicated significant up or downregulation of 18 host immune- or anti-infection-related genes post 12 to 60 hpi following the infection. Additionally, RNA sequencing (RNA-seq) unveiled 7 hub differentially expressed genes (DEGs) and 11 encoded proteins play crucial roles in the anti-V. harveyi response in American eels. This study firstly represents the comprehensive report on the pathogenicity of V. harveyi to American eels and RNA-seq of host's response to V. harveyi infection. These findings provide valuable insights into V. harveyi pathogenesis and the strategies employed by the host's immune system at the transcriptomic level to combat V. harveyi infection.

Transcriptome analysis of Macrobrachium rosenbergii hemocytes in response to Staphylococcus aureus infection

The aquaculture industry has suffered significant financial losses as a result of disease outbreaks. In particular, disease outbreaks have become a major problem that can seriously affect the sustainable development of the Macrobrachium rosenbergii aquaculture industry. It is crucial to determine the defense mechanism of the host after pathogenic invasion in order to provide effective defense measures after disease outbreaks. Shrimp, like other invertebrates, primarily depend on their innate immune systems to defend against pathogens, and recognize and resist pathogens through humoral and cellular immune responses. In this investigation, we used RNA-seq technology to investigate the transcriptome of hemocytes from M. rosenbergii induced by Staphylococcus aureus. Our main targets were immune pathways and genes related to innate immunity. RNA-seq identified 209,069 and 204,775 unigenes in the control and experimental groups, respectively. In addition, we identified 547 and 1734 differentially expressed genes (DEGs) following S. aureus challenge after 6 and 12 h (h), respectively. GO and KEGG enrichment analysis revealed that the DEGs were significantly enriched in several biological signalling pathways, including NOD-like receptor, PI3K-Akt, Toll and Imd, IL-17, TGF-beta, RIG-I-like receptor, cAMP, apoptosis, and C-type lectin receptor. Sixteen DEGs were chosen at random for qPCR verification; these results concurred with those from sequencing. Our findings revealed that immune-related genes play an important role in antibacterial activities and have specific functions for gram-positive bacteria. These results provide more data for the prevention of M. rosenbergii diseases and offer a basis for the better prevention of diseases.

Applying genetic technologies to combat infectious diseases in aquaculture

Disease and parasitism cause major welfare, environmental and economic concerns for global aquaculture. In this review, we examine the status and potential of technologies that exploit genetic variation in host resistance to tackle this problem. We argue that there is an urgent need to improve understanding of the genetic mechanisms involved, leading to the development of tools that can be applied to boost host resistance and reduce the disease burden. We draw on two pressing global disease problems as case studies-sea lice infestations in salmonids and white spot syndrome in shrimp. We review how the latest genetic technologies can be capitalised upon to determine the mechanisms underlying inter- and intra-species variation in pathogen/parasite resistance, and how the derived knowledge could be applied to boost disease resistance using selective breeding, gene editing and/or with targeted feed treatments and vaccines. Gene editing brings novel opportunities, but also implementation and dissemination challenges, and necessitates new protocols to integrate the technology into aquaculture breeding programmes. There is also an ongoing need to minimise risks of disease agents evolving to overcome genetic improvements to host resistance, and insights from epidemiological and evolutionary models of pathogen infestation in wild and cultured host populations are explored. Ethical issues around the different approaches for achieving genetic resistance are discussed. Application of genetic technologies and approaches has potential to improve fundamental knowledge of mechanisms affecting genetic resistance and provide effective pathways for implementation that could lead to more resistant aquaculture stocks, transforming global aquaculture.

Integrative time series of cellular, humoral and molecular response revealed immunotoxicity of bifenthrin to Chinese rare minnow (Gobiocypris rarus) following Pseudomonas fluorescens challenge

Bifenthrin is a common pesticide that is widespread in aquatic environments. Although it has been shown to be toxic to aquatic organisms, its immunotoxicity and mechanism are unclear. Herein, we reported the immunotoxicity of bifenthrin on adult Chinese rare minnow (Gobiocypris rarus) after 28 days of exposure to different concentrations of bifenthrin (0.1, 0.3, and 1.0 μg/L) and 36-h Pseudomonas fluorescens challenge. Bifenthrin inhibited the fish humoral immune response to bacteria by altering the lymphocyte and neutrophil ratios and decreasing the production of lysozyme, complement component 3, immunoglobulin M, and C-reactive protein, particularly were 1.0 μg/L. Bifenthrin caused intestinal damage and significantly reduced the volume of intestinal mucus at 12 and 36 hours postinjection (hpi) (p < 0.05). Moreover, 1.0 μg/L bifenthrin significantly increased the fish mortality and bacterial loads at 12 and 36 hpi (p < 0.05). RNA-seq analysis revealed several enriched genes involved in pathogen attachment and recognition, inflammatory responses, and complement system at the early-to-mid stage of infection (4-12 hpi). Overall, our results corroborated that bifenthrin induced immunotoxicity in Gobiocypris rarus, resulting in immune dysfunction of fish and increasing their sensitivity to bacterial infection and accelerating mortality. Moreover, 4-12 hpi was better than 36 hpi for analyzing immune responses against pathogen infection in fish exposed to bifenthrin.

GWAS on Imputed Whole-Genome Sequence Variants Reveal Genes Associated with Resistance to Piscirickettsia salmonis in Rainbow Trout (Oncorhynchus mykiss)

Genome-wide association studies (GWAS) allow the identification of associations between genetic variants and important phenotypes in domestic animals, including disease-resistance traits. Whole Genome Sequencing (WGS) data can help increase the resolution and statistical power of association mapping. Here, we conduced GWAS to asses he facultative intracellular bacterium Piscirickettsia salmonis, which affects farmed rainbow trout, Oncorhynchus mykiss, in Chile using imputed genotypes at the sequence level and searched for candidate genes located in genomic regions associated with the trait. A total of 2130 rainbow trout were intraperitoneally challenged with P. salmonis under controlled conditions and genotyped using a 57K single nucleotide polymorphism (SNP) panel. Genotype imputation was performed in all the genotyped animals using WGS data from 102 individuals. A total of 488,979 imputed WGS variants were available in the 2130 individuals after quality control. GWAS revealed genome-wide significant quantitative trait loci (QTL) in Omy02, Omy03, Omy25, Omy26 and Omy27 for time to death and in Omy26 for binary survival. Twenty-four (24) candidate genes associated with P. salmonis resistance were identified, which were mainly related to phagocytosis, innate immune response, inflammation, oxidative response, lipid metabolism and apoptotic process. Our results provide further knowledge on the genetic variants and genes associated with resistance to intracellular bacterial infection in rainbow trout.

New insights into β-glucan-enhanced immunity in largemouth bass Micropterus salmoides by transcriptome and intestinal microbial composition

β-glucan is widely used in aquaculture due to its immunostimulatory effects, but the specific effect and potential regulatory mechanism on largemouth bass (Micropterus salmoides) are still unclear. Here, we evaluated the effects of β-glucan on growth, resistance to Aeromonas schubertii, intestinal health, and transcriptome of largemouth bass to reveal the potential regulators, metabolic pathways, and altered differential microbiota. Four experimental diets were designed with β-glucan supplementation levels of 0 (control), 100 (LA-100), 200 (MA-200), and 300 (HA-300) mg kg^-1, and each diet was fed to largemouth bass (79.30 ± 0.50 g) in triplicate for 70 days, followed by a 3-day challenge experiment. Results showed that different β-glucan supplementations had no significant effects on growth performance and whole-body composition. Fish fed a diet with 300 mg kg^-1 β-glucan significantly increased the activity of lysozyme than those fed diets with 0 and 100 mg kg^-1 β-glucan. In addition, the survival rate of largemouth bass in β-glucan supplementation groups was significantly higher than the control group at 12- and 24-h challenge by Aeromonas schubertii. Transcriptome analysis showed that a total of 1,245 genes were differentially expressed [|log₂(fold change)| ≥1, q-value ≤0.05], including 109 immune-related differentially expressed genes (DEGs). Further analysis revealed that significantly upregulated and downregulated DEGs associated with immunity were mapped into 12 and 24 pathways, respectively. Results of intestinal microflora indicated that fish fed a diet with 300 mg kg^-1 β-glucan had higher bacterial richness and diversity as evaluated by Sobs, Chao, Ace, and Simpson indices, but no significant differences were found in the comparison groups. Furthermore, 300 mg kg^-1 β-glucan significantly increased the relative abundance of Mycoplasma and decreased Proteobacteria (mainly Escherichia-Shigella and Escherichia coli) and Bacillus anthracis in largemouth bass intestinal microflora. The findings of this study provided new insights that will be valuable in future studies to elucidate the mechanism of immunity enhancement by β-glucan.