Abstract:Forty-nine lactic acid bacteria strains were isolated from sediment samples from cultured ponds of sea cucumbers (Apostichopus japonicus) in Dongying, Shandong Province, in May 2017. First, antagonistic bacterial experiments were conducted using Vibrio splendidus and Pseudoalteromonas nigrifaciens, which are the main pathogenic bacteria of “skin ulcer syndrome” for sea cucumbers, and a lactic acid bacteria CLY-5, which has demonstrated significant bacteriostatic activity. Next, physiological and biochemical experiments and a similarity analysis of 16S rDNA sequences as well as the growth character of CLY-5 were carried out. A safety experiment for sea cucumbers was also performed. The results revealed that CLY-5 strain successfully inhibited V. splendidus and P. nigrifaciens. Meanwhile, the strain’s intracellular and extracellular products effectively inhibited V. splendidus and P. nigrifaciens, as demonstrated by inhibition zone diameters of 20 mm, 23 mm, and 27 mm, 38 mm, respectively, with extracellular products showing superior performance compared with intracellular products. Dipping bath concentrations were set to 1×109, 1×108, and 1×107 CFU/ml to test the safety of CLY-5 for sea cucumbers. During the experiment, all sea cucumbers were in good conditions. Based on the 16S rDNA sequence analysis, strain CLY-5 was determined to be identical to Lactobacillus plantarum NR117813.1. In addition, strain CLY-5 exhibited superior growth at 30℃~44℃ and salinities of 6 to 8. Moreover, CLY-5 came into a logarithmic growth phase after 20 h of cultivation and reached peak growth after 28~32 h. In summary, strain CLY-5 could be used to reduce the occurrence of sea cucumber disease and is also suitable for pond culture environment. These results provide a basis for ecological prevention strategies in disease control, and should prove useful in the development and utilization of lactic acid bacteria.
