Bdellovibrio lyse multiple pathogenic bacteria and protect crucian carp Carassius auratus gibelio from Aeromonas veronii infections

Bdellovibrio are obligate predators of Gram-negative bacteria that could parasitize other bacteria and cause their lysis. It has been considered as a potential probiotic and may replace antibiotics. In order to better explore the inhibitory activity of Bdellovibrio against common aquatic pathogens and its potential use in aquaculture, the Aeromonas hydrophilia was used as the host bacteria for culturing Bdellovibrio. An absolute qPCR detection system with specific primers were also established for the amount determination of Bdellovibrio sp. . The morphological characteristics of the cultured Bdellovibrio sp. were detected by scanning electron microscope. By detecting absorbance at OD 600nm and double layer plates plaque experiments, the Bdellovibrio sp. exhibited a certain lysis effect on the selected aquatic pathogens including Aeromonas veronii , Aeromonas hydrophil ia , Vibrio fluvialis , Escherichia coli , Vibrio anguillarum , Vibrio cholerae and Citrobacter freundii. Adding the cultured Bdellovibrio sp. to water could significantly reduce the mortality rate of Carassius auratus caused by the infections with A. vironii. Meanwhile, the amount of Bdellovibrio sp. on intestines and gills of C. auratus could increase over time after treatment, indicating Bdellovibrio may colonized in fish. The present study revealed that Bdellovibrio may play important roles as an alternative to antibiotics in protecting aquatic animals from pathogenic bacteria. These results will provide a certain theoretical basis for the application of Bdellovibrio in aquaculture. • An absolute qPCR detection system was established for the amount determination of Bdellovibrio sp. • The cultured Bdellovibrio sp. exhibited a certain lysis effect on aquatic pathogenic bacteria. • Bdellovibrio sp. significantly reduce the mortality rate of C. auratus infected with A. vironii. • The amount of Bdellovibrio sp. on intestines and gills of C. auratus increase over time after treatment.