Bdellovibrio and like organisms promoted growth and survival of juvenile abalone Haliotis discus hannai Ino and modulated bacterial community structures in its gut

In this study, Bdellovibrio and like organisms (BALOs) strain BDH12 that possessed a wide lysis spectrum was tested in coldwater abalone ( Haliotis discus hannai Ino) juvenile rearing, and its effect on survival and growth and on gut bacterial communities was investigated. A 90-day rearing experiment at the production level was performed. At the end, juvenile abalone grew from the initial shell length of 4.0 ± 1.0 to 12.63 ± 2.12 mm in control and 14.89 ± 1.27 mm in test ( p < 0.05). With the addition of BDH12, abalone survival rate, percentage weight gain, shell length gain, and average daily growth in test reached 63.3 ± 1.87%, 6834 ± 39%, 272 ± 15%, and 4.56 ± 1.18 mg day −1 , respectively, significantly ( p < 0.05) higher than those in control, viz., 41.8 ± 3.36%, 4168 ± 47%, 216 ± 17%, and 2.78 ± 1.37 mg day −1 , respectively. Total cultivable Vibrio counts (TCVC) and bacterial counts (TCBC) were enumerated by conventional culturing. Compared to control, TCVC and TCBC in test were reduced by 2.39 and 4.07 log colony forming units·mL −1 , respectively, in rearing water ( p < 0.05), and by 3.54 and 4.11 log CFU·g −1 , respectively, in abalone guts ( p < 0.05). Strong negative correlations were found between abalone shell length/weight with TCBC/TCVC in rearing water/guts ( p < 0.01). Additionally, 16S rDNA-PCR and denaturing gradient gel electrophoresis profiles revealed that of the 27 species/strains sequenced, 51.85% (14) were shared by both control and test and 22.22% (6) reduced, of which 33.33% (2) were Vibrio. The results of this study demonstrated that BDH12 can be beneficially applied in coldwater abalone rearing.