Xuemei Yuan

Nocardia seriolae infection poses a serious threat to largemouth bass (Micropterus salmoides) aquaculture, owing to the lack of effective control strategies. This study investigated the antibacterial effects and underlying mechanisms of Macleaya cordata alkaloids—sanguinarine (SE) and chelerythrine (CHE)—against N. seriolae through integrated physiological and transcriptomic approaches. Results showed SE and CHE exhibited strong in vitro antibacterial activity, with minimum inhibitory concentrations (MICs) of 62.5 and 7.8 μg/mL, respectively. In vivo trials revealed that dietary supplementation with either alkaloid significantly enhanced the survival of infected fish, yielding relative percent survival (RPS) values of 34.5% for SE and 40.0% for CHE. Concurrently, both treatments reduced bacterial load and alleviated granulomatous pathology in multiple organs, including the liver, spleen, and kidney. Physiological analyses revealed severe damage to the cell envelope, as evidenced by increased membrane permeability and structural disintegration observed under transmission electron microscopy (TEM). Transcriptomic profiling identified 3708 and 5095 differentially expressed genes (DEGs) in the SE- and CHE-treated groups, respectively, with notable downregulation of key genes involved in peptidoglycan biosynthesis, the citrate cycle, oxidative phosphorylation, and the pentose phosphate pathways. These findings demonstrate that SE and CHE inhibit N. seriolae through a multi-target mechanism simultaneously disrupting cell envelope integrity and energy production, laying the groundwork for their development as eco-friendly aquaculture therapeutics.

Trionyx sinensis hemorrhagic syndrome virus (TSHSV) is an aquatic arterivirus causing a high mortality rate for T. sinensis (Chinese soft-shelled turtle), but the detailed infection properties of TSHSV are unclear, and no effective treatment is available. In this study, cell culture and histopathology were performed to elucidate the infection properties of TSHSV. Furthermore, the anti-TSHSV and immune-enhancing effects of curcumin were evaluated using survival statistics, qPCR, and tissue immunofluorescence. The results demonstrated that TSHSV could proliferate in the spleen cell line of T. sinensis, leading to cytopathic effects. TSHSV damaged the livers, kidneys, and lungs, characterized by cell disintegration and hyperemia. Curcumin at 250 mg/kg improved the survival of T. sinensis, and significantly reduced the viral load in the spleens, kidneys, and lungs. Moreover, curcumin inhibited the mRNA expression of immune-related genes, RSAD2, IFN-γ, and TNF-α (p < 0.05). In conclusion, these results imply that TSHSV is pathogenic to the spleen cell line, liver, spleen, kidney, and lung of T. sinensis. Curcumin effectively inhibits TSHSV and modulates the immune function of T. sinensis, so it holds promise as a means to prevent TSHSV.

The Chinese soft-shelled turtle (Pelodiscus sinensis) is an important aquaculture reptile with rich nutritional and medicinal values. In recent decades, the wild resources of P. sinensis have been depleting due to natural and artificial factors. Herein, we report the complete mitochondrial genome of four P. sinensis strains, including the Japanese (RB) strain, Qingxi Huabie (HB) strain, Jiangxi (JB) strain, and Qingxi Wubie (WB) strain. The nucleotide composition within the complete mitogenomes was biased towards A + T with a variable frequency ranging from 59.28% (cox3) to 70.31% (atp8). The mitogenomes of all four strains contained 13 protein-coding genes (PCGs), 22 tRNAs, 2 rRNAs, 1 control region, and a replication origin region of the L-strand replication (OL), which was consistent with most vertebrates. Additionally, the atp8, nad4l, nad6, and nad3 genes possessed high genetic variation and can be used as potential markers for the identification of these P. sinensis strains. Additionally, all PCGs genes were evolving primarily under purifying selection. Through comparative analysis, it was revealed that most of the tRNAs were structurally different in the TψC stem, DHU stem, and acceptor stem. The length of the tandem repeats in the control region was variable in the four P. sinensis strains, ranging from 2 bp to 50 bp. Phylogenetic analysis indicated that all P. sinensis strains clustered into one branch and were closely related to other Trionychinae species. Overall, this study provides mitochondrial genome information for different P. sinensis strains to support further species identification and germplasm resource conservation.

The pathogenic Bacillus cereus strain XS0724 isolated from China can cause high lethality to Trionyx sinensis, but little information is available on their detailed interactions. In this study, histopathologic profiling indicated that B. cereus caused vacuolization and cell necrosis in the liver, spleen, kidney, and intestine. The identification of the virulence factor genes non-hemolytic enterotoxin (Nhe), hemolysin BL (Hbl), and enterotoxin FM (entFM) confirmed bacterial pathogenicity. Splenic transcriptomic sequencing at 96 h post-infection identified various immune-related genes mapped to diverse gene families, including interleukin, complement, chemokine, and interferon. The differentially expressed genes (DEGs) were enriched in 2174 GO terms: 1694 in biological processes, 138 in cellular components, and 342 in molecular functions. Further KEGG enrichment indicated that DEGs were primarily associated with the phagosome, NF-kappa B signaling pathway, and PI3K-Akt signaling pathway. The DEGs and enriched pathways may be involved in the elimination of invasive B. cereus. These data laid the foundation for elucidating the potential molecular mechanisms in this bacterial infection process, and provided robust genetic evidence for subsequent work on resistance genes of T. sinensis.

The giant freshwater prawn, Macrobrachium rosenbergii, is an economically important crustacean and is farmed in many countries. Since 2009, a larval mortality syndrome of M. rosenbergii has broken out and spread widely in the main breeding area, including Zhejiang, Jiangsu, Guangxi, and Guangdong Provinces in mainland China. A novel virus, named Macrobrachium rosenbergii Taihu virus (MrTV), was isolated from the moribund larvae and was determined to be the causative agent of the M. rosenbergii larval mortality syndrome by experimental infection. Further genomic sequencing suggested that the MrTV genome is monopartite, 10,303 nt in length, and dicistronic with two non-overlapping open reading frames (ORFs) separated by an intergenic region (IGR) and flanked by untranslated regions (UTRs). Phylogenetic analysis using the full-length genomic sequence and the putative amino acid sequences of the capsid protein revealed that MrTV was more closely related to the taura syndrome virus (TSV) than to any other viruses. According to these molecular features, we proposed that MrTV is a new species in the genus Aparavirus, family Dicistroviridae. These results may shed light on controlling larval mortality syndrome in M. rosenbergii.