Biological characterization of two marine Bdellovibrio-and-like organisms isolated from Daya bay of Shenzhen, China and their application in the elimination of Vibrio parahaemolyticus in oyster.

Bdellovibrio-and-like organisms (BALOs) are a group of highly motile delta-proteobacteria that prey on other gram-negative bacteria. However, nothing is known of the application potential of marine BALOs in safeguarding seafood safety. Here, biological characterization of two marine BALOs strains and their application in the elimination of Vibrio parahaemolyticus in oyster (Crassostrea ariakensis) at the laboratory scale were investigated. BALOs strains BDH12 and BDHSH06 were isolated from sediment of Daya bay in Shenzhen of China, with Shewanella putrefaciens strain 12 and V. parahaemolyticus strain SH06 as preys, respectively, when using double layer agar technique. They were identified as BALOs morphologically by transmission electron microscopy, while partial 16S rDNA sequencing analysis revealed that they showed no close relationships with members of the known genera Bdellovibrio, Bacteriolyticum, Bacteriovorax, or Peredibacter. Biological characterizations revealed that both strains had the optimal pH, salinity and temperature at 7.2, 3% and 30 °C, correspondingly. They could not utilize autoclaved, dead cells as hosts. Prey range analysis revealed that individually, BDH12 and BDHSH06 lysed 82.5% (47 strains) and 84.2% (48 strains) of the total 57 preys tested respectively. In combination, they lysed 98.2% (56 of 57) strains. All strains of V. parahaemolyticus, Vibrio cholerae and Vibrio alginolyticus tested could be lysed by both strains. A 7-day laboratory-scale V. parahaemolyticus elimination experiment in oyster showed that in the control, the cell counts of total vibrios and V. parahaemolyticus strain Vp plus in water and in oyster intestines were on the rise, whereas in the BALOs treated groups, their numbers were down from 8.09±0.05 log CFU/ml and 8.02±0.04 log CFU/ml to 2.39±0.01 log CFU/ml and 2.33±0.01 log CFU/ml, respectively. The same patterns could also be observed in oyster intestines. Results of this study indicate the feasibility of using BALOs to biologically control or even eliminate V. parahaemolyticus in seafood oyster.