To explore whether a probiotic complex composed of Lactobacillus rhamnosus, Lactobacillus plantarum, and Lactobacillus casei can prevent or inhibit the inflammatory response caused by the invasion of Plesiomonas shigelloides in the southern catfish, we screened differentially expressed genes and enriched inflammation-related pathways among a control and three experimental groups and conducted analysis by transcriptome sequencing after a 21-day breeding experiment. Compared with those in the PS (Plesiomonas shigelloides) group, southern catfish in the L-PS (Lactobacillus-Plesiomonas shigelloides) group had no obvious haemorrhages or ulcerations. The results also showed that inflammation-related genes, such as mmp9, cxcr4, nfkbia, socs3, il-8, pigr, tlr5, and tnfr1, were significantly upregulated in the PS group compared with those in the L-PS groups. In addition, we verified six DEGs (mmp9, cxcr4, nfkbia, socs3, rbp2, and calr) and three proteins (CXCR4, NFKBIA, and CALR) by qRT-PCR and ELISA, respectively. Our results were consistent with the transcriptome data. Moreover, significantly downregulated genes (p < 0.05) were enriched in inflammation-related GO terms (lymphocyte chemotaxis and positive regulation of inflammatory response) and immune-related pathways (intestinal immune network for IgA production and IL-17 signalling pathway) in the L-PS vs. the PS group. Our results indicate that the infection of P. shigelloides can produce an inflammatory response, and probiotics could inhibit the inflammatory response caused by P. shigelloides to some extent.

4-Nonylphenol (4-NP), an important fine chemical precursor, can cause endocrine disruption, resist natural degradation, and bioconcentrate. Biodegradation is an effective and environmentally sustainable approach to its remediation. This study employed a mixture comprising equal proportions of six non-pathogenic Bacillus strains to screen and identify strains capable of degrading 4-NP, and degradation rate was measured using an ELISA kit, and metabolomic analyses and whole-genome sequencing were used to investigate the response of Bacillus to 4-NP and elucidate pathways involved in 4-NP degradation. The results revealed DY and LY strains isolated at 500 μg/L 4-NP. The DY strain was identified as Bacillus thuringiensis, and the LY strain was identified as Bacillus cereus via physiological, biochemical and PCR analyses. The degradation efficiency of a DY and LY strain mixture was 79.45% after 7 days. At 1000 μg/L 4-NP, only the LY strain was successfully isolated. Whole-genome sequencing indicated that the LY strain (accession number: CRA021210) shares the highest homology with B. cereus strain FORC-047. Notably, it showed a degradation rate of 86.34% after 7 days. Metabolomics analysis indicates that 4-NP affects the degradation pathways of aromatic compounds and benzoic acid in B. cereus. Combined with genome data, it is hypothesized that the 4-NP degradation pathway involves its conversion to p-hydroxybenzoic acid, catalyzed by monooxygenases, dioxygenases and oxidases. Subsequently, p-hydroxybenzoic acid degrades via one of two potential pathways: it produces phenol through decarboxylase or is oxidized to benzoic acid by monooxygenase. In summary, the DY and LY strains are capable of degrading 4-NP. Furthermore, we postulate potential 4-NP degradation pathways, providing insights for the remediation of 4-NP in aquatic environments.

Nonylphenol (NP) bioremediation is constrained by the scarcity of efficient and non-pathogenic degrading strains. To clarify the role of acetyl-CoA C-acetyltransferase (AtoB) in NP degradation, we generated an atoB-overexpressed strain (LY-OE) from the environmentally tolerant Bacillus cereus LY and compared its degradation rate with the wild type using HPLC. Untargeted lipidomics was conducted to characterize metabolic responses under NP stress, and key differential lipid metabolites (DELMs) were further validated by ELISA. Additionally, AtoB concentration and ATP content were quantified using commercial assay kits in Bacillus cereus. LY-OE showed a markedly higher NP degradation rate (96%) than LY (85%). Lipidomic analysis identified 34 significant DELMs (VIP > 1, p < 0.05), including elevated cardiolipin (CL) and phosphatidylglycerol (PG), and reduced phosphatidylcholine (PC) and triglycerides (TG). ELISA confirmed these changes (p < 0.01 or p < 0.001), consistent with lipidomic findings. LY-OE showed significantly higher AtoB concentration during the logarithmic growth phase and exhibited higher ATP content during NP degradation. These findings suggest that atoB overexpression enhances NP degradation by both boosting energy supply and remodeling lipid metabolism. This work identifies atoB as a key factor for NP biodegradation and provides a promising strategy for developing high-performance bioremediation strains.

Nonylphenol (NP), a typical emerging pollutant, is widely detected in water bodies, yet its hepatotoxic mechanisms and mitigation strategies remain underexplored. This study evaluated the protective effects of a mixed probiotic (Lactobacillus acidophilus and Bacillus subtilis) against NP-induced hepatotoxicity in Silurus meridionalis by integrating transcriptomic and metabolomic analyses, with validation by RT-qPCR and ELISA. The results showed that NP exposure disrupted the arachidonic acid (AA) pathway (activating pro-inflammatory COX and LOX pathways while the suppressing anti-inflammatory CYP450 branch), promoted ferroptosis via iron dyshomeostasis and oxidative damage, and impaired triglyceride (TG) synthesis. Probiotic pretreatment reversed these toxic effects by modulating AA metabolism, suppressing COX (ptgs2a↓ → PGE₂↓) and LOX (alox12↓ → MDA↓) pathways, while upregulating the CYP450 pathway (cyp2j↑ → 11,12-EET↑). Probiotics also enhanced Fe³⁺ sequestration (steap4↑) and antioxidant defense (CAT↑, gpx4a↑), limiting Fenton reaction-mediated oxidative injury, and restored hepatic TG synthesis through upregulation of the DHAP-to-TG cascade (DHAP—(gpd1b↑) → G3P↑—(gpat3↑) → LPA—(agpat6↑) → PA—(plpp7↑) → DAG↑—(dgat2↑) → TG↑). These findings suggest that NP induces hepatotoxicity in S. meridionalis, involving ferroptosis, AA metabolism disruption and impaired TG synthesis as interconnected pathological events. Probiotics likely counteract this toxicity through systemic metabolic reprogramming. Collectively, these findings elucidate the hepatotoxic mechanisms of NP in S. meridionalis and offer toxicological data for its risk assessment, supporting the potential of probiotic-based strategies to mitigate emerging pollutant impacts in aquatic organisms.

Frequent bacterial outbreaks in aquaculture threaten commercial fish, with Plesiomonas shigelloides being notably common due to its lipa gene, a critical virulence factor. This study overexpressed the lipa gene in fish-derived P. shigelloides to investigate its impact on biofilm formation, LIPA activity, and bacterial adhesion. We infected Silurus meridionalis for 7 d to assess pathogenicity, observing symptoms, and collected the head kidney for transcriptome and proteomic analysis. Results were confirmed by qPCR and ELISA, and we performed GO classification, KEGG pathway, and protein interaction network analysis on differentially expressed immune proteins. The findings revealed that lipa overexpression increased biofilm formation (p < 0.01), lipoyl synthase activity (p < 0.01), and bacterial adhesion compared to wild-type strains, offering novel insights into its function. In Silurus meridionalis, this overexpression led to increased hemorrhaging in the anal and caudal fins compared to the wild-type and control groups. Furthermore, q-PCR and ELISA results demonstrated that the expression levels of NACHT/LRR/PYD domain-containing protein 4 (NLRP4), complement component 6 (C6), and lysozyme C (LZMC) correlated with the transcriptome and proteomic data. Overall, lipa overexpression enhances P. shigelloides virulence and intensifies the immune responses in Silurus meridionalis, providing insights into its pathogenic mechanism and supporting healthy breeding of Silurus meridionalis.

As a ubiquitous environmental endocrine disruptor, nonylphenol (NP) threatens aquatic organisms, driving the need for sustainable mitigation strategies. Wh