Isolation and identification of a strain of Pseudomonas putida and its effect on histopathology, apoptosis, and gene expression in turbot (Scophthalmus maximus).

Turbot (Scophthalmus maximus) is one of the most widely species that boasts high economic value in the aquaculture industry. In spite of the exponential growth of aquaculture, infectious bacterial diseases have caused great economic losses in turbot industry. This study isolated and identified a strain of Pseudomonas putida, denoted as DY16, and it is a conditionally pathogenic bacterium, therefore we conducted the following research on it. The morphological, physicochemical, and genomic characteristics of bacteria and their pathogenic mechanisms were analyzed by morphological and biochemical characterization and genome sequencing. P. putida effects on the histology and immune-related gene response of turbot were then assessed. Histopathology and TUNEL assay showed that P. putida caused severe damage and induced apoptosis in the gills, intestines, spleen, and liver of turbot, respectively. In addition, this study indicated that the immune-related genes, such as ap4m1, prkca, traf4, itgb4, glb1, and mylk in various turbot tissues after infection with P. putida. Hence, it was hypothesized that these genes could be involved in host immune response and gene regulation in P. putida. Conclusively, P. putida infection caused pathological changes in the gills, intestines, spleen, and liver tissues of turbot and induced significant apoptotic and immune responses. These findings provide useful information and a theoretical basis for further understanding the immune defense mechanisms of P. putida and turbot offering guidance for the prevention and treatment of bacterial diseases in fish.