A research team has found that increased expression of the lipa gene in Plesiomonas shigelloides is associated with stronger bacterial attachment, greater biofilm formation, and more severe disease symptoms in southern catfish ( Silurus meridionalis ). The altered bacteria also triggered substantial changes in the fish’s immune response, linking a bacterial metabolic gene to both infection characteristics and host defenses. The findings identify lipoyl synthase, the enzyme associated with lipa , as a potential target for future research into controlling bacterial infections and improving fish health in aquaculture.
Bacterial diseases pose persistent challenges for intensive aquaculture, where outbreaks can damage fish health and cause substantial economic losses. P. shigelloides is a fish pathogen associated with inflammation, hemorrhage, and tissue damage. Previous research has identified several genes potentially involved in its pathogenicity, while studies in other bacteria have connected lipoic acid synthesis with metabolism and interactions with host immunity. However, how lipa expression relates to infection in fish remains poorly understood. In particular, researchers have lacked an integrated picture of how changes in this gene affect bacterial attachment and biofilm formation alongside immune responses in the host. Addressing that gap could help identify molecular targets for more precise disease management.
A study (DOI: 10.48130/jai-0026-0005 ) published in Journal of Applied Ichthyology on 21 September 2026 by Ranran Dong's team, Guizhou University, reports that elevated lipa expression accompanies enhanced bacterial virulence traits, more pronounced disease symptoms, and altered immune responses in southern catfish.
Researchers constructed a lipa -overexpressing strain from bacteria previously isolated from diseased southern catfish and compared it with the wild-type strain. Laboratory assays measured lipoyl synthase, biofilm formation, attachment to fish surface mucus, and bacterial growth. The team then challenged catfish with equal concentrations of either bacterial strain, while a control group received sterile saline. Disease symptoms were observed, and head kidney tissue, an important immune organ in fish, was collected after seven days. RNA sequencing and data-independent acquisition proteomics were used to profile changes in gene and protein expression. Functional enrichment and protein interaction analyses explored the biological processes involved, while quantitative PCR and ELISA provided additional checks on selected findings. The laboratory comparisons showed that the overexpressing strain produced significantly higher lipoyl synthase assay readings and more biofilm than wild-type bacteria. Microscopy also revealed denser bacterial aggregates on fish mucus, with average counts rising from 903 to 1,339 bacteria per field. Growth measurements showed a two-hour delay followed by a higher plateau, indicating that the altered strain also had different growth characteristics. Within 72 hours of infection, fish exposed to the overexpressing strain displayed more pronounced symptoms, including excessive mucus, fin hemorrhage, cloacal swelling, and necrotic lesions; saline-treated fish showed no lesions. Comparing infected groups identified 476 differentially expressed genes and 350 differentially expressed proteins, including 66 immune-related proteins. Analyses highlighted responses associated with hemostasis, coagulation, the membrane attack complex, and NOD-like receptor signaling. Complement component C6, NLRP4, and lysozyme C emerged as prominent immune factors, with selected molecular measurements supporting the broader profiling results. Together, these observations connect increased lipa expression with changes in bacterial behavior and the host's response to infection. They also provide a combined molecular dataset for investigating how bacterial metabolism and fish immune defenses interact during disease development in this experimental model.
The study provides a foundation for investigating lipa as a candidate target for infection control, but its precise mechanisms remain unresolved. Because the researchers could not generate a gene knockout strain, the findings do not establish the gene's necessity for the observed effects. Proposed roles for adhesion structures, biofilm matrix production, and bacterial communication also require direct testing. Further experiments could clarify whether disrupting this pathway offers practical benefits for protecting farmed fish.|
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References
DOI
Original Source URL
https://doi.org/10.48130/jai-0026-0005
Funding information
This work was supported by the National Natural Science Foundation of China (32460918).
About Journal of Applied Ichthyology
Journal of Applied Ichthyology (e-ISSN 1439-0426; p-ISSN 0175-8659) is an open-access, peer-reviewed journal dedicated to publishing high-quality research on applied ichthyology, aquaculture, and marine fisheries, including management of fisheries resources, fisheries ecology, fish health and pathology.
Journal of Applied Ichthyology
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From gene to disease: the virulence amplification of Plesiomonas shigelloides via lipa overexpression
21-Sep-2026
The authors declare that they have no competing interests.