Molecular typing and identification ofBdellovibrio-and-like organisms isolated from seawater shrimp ponds and adjacent coastal waters

Abstract

To apply and compare two PCR-based methods for typing saltwater Bdellovibrio-and-like organisms (BALOs) and to understand ecological and phylogenetic aspects of the BALOs isolated from shrimp mariculture systems. Using double-layer agar technique, the numbers of culturable BALOs that lyse Vibrio alginolyticus were found to be 10-10(3) PFU ml(-1) in the surface water samples. A total of 130 BALOs isolates were differentiated into five phylotypes by denaturing gradient gel electrophoresis targeting the 16S rDNA V3 region and four phylotypes by amplified rDNA restriction analysis of the Bacteriovoracaceae-specific 16S rDNA fragment respectively. Phylogenetic analysis of representative isolates showed that all of them were identified as Bacteriovorax spp., but affiliated with four different clusters in the family Bacteriovoracaceae. The two PCR-based methods both can be chosen to rapidly type the saltwater BALOs at cluster level. And the relatively large numbers of BALOs with various phylotypes recovered from the same habitats suggested that these predators might play important ecological role in shrimp mariculture environments. We proposed two effective methods to distinguish rapidly large numbers of BALOs isolates and our results would be helpful to understand the diversity and function of BALOs in mariculture environments.