Selection, identification and application of antagonistic bacteria associated with skin ulceration and peristome tumescence of cultured sea cucumber Apostichopus japonicus (Selenka)

The aquaculture of the sea cucumber Apostichopus japonicus has grown rapidly over recent years in China and become an important sector of the marine industry. However, with rapid growth and the use of non-standard practices and culture techniques, epidemic diseases of A. japonicus now pose increasing problems to the industry. Prevention and control of diseases seriously affecting aquaculture of A. japonicus, a major marine industry in China, are essential for its development. We have previously isolated two pathogenic bacteria Pseudoalteromonas sp and Pseudoalteromonas tetraodonis associated with ulceration and peristome tumescence of A. japonicus. In this study, we isolated 266 bacteria from A. japonicus and its cultural environment, and identified 5 bacteria Vibrio ordalii, Bacillus safensis, P. tetraodonis, Pseudoalteromonas elyakovii and Pseudomonas segetis with strong antimicrobial activity to P. sp and P. tetraodonis using point inoculation, filter paper and Oxford cylinder methods. Further investigation on their growth and antagonistic characteristics indicated that 1) V. ordalii has the strongest antimicrobial ability even at low temperature and its extracellular products precipitated with ammonium sulfate at different growth stages also have antimicrobial activity; 2) P. tetraodonis and P. elyakovii only have antimicrobial activity at 28 °C and their extracellular products at different growth stages also have strong antagonistic effects; 3) the extracellular products of B. safensis at different growth stages have no antibacterial activity. Injection of extracellular products of P. elyakovii and V. ordalii into A. japonicus can enhance its non-specific immune-related enzyme activities and disease resistance. The study provides a theoretical basis and products for A. japonicus disease prevention and healthy aquaculture.

► P. sp and P. tet are causes of skin ulceration and peristome tumescence in A. japonicus.
► V. ordalii, B. safensis, P. tet, P. elyakovii and P. segetis are antimicrobial.
► Different extracellular products have different antimicrobial activities.
► Injection of the extracellular products enhances disease resistance of A. japonicus.