Abstract:[Objective] To investigate the characteristics of culturable microorganisms and the genetic diversity of dominant pathogens during shrimp postlarva bacterial vitrified syndrome (BVS) of Litopenaeus vannamei in the factory breeding system. [Methods] The composition and structural characteristics of culturable bacterial communities in shrimp (parent shrimp, fertilized egg, nauplius, zoea, mysis, and postlarva), water, and bait samples at different breeding stages were studied by in vitro bacterial culture method combined with gene sequencing technology, and the genetic diversity of the pathogenic bacteria was studied by multilocus sequence analysis (MLSA). [Results] The 526 isolates with typical morphological differences and community dominance belonged to 113 species, 38 genera, 24 families, 16 orders, 5 classes, and 4 phyla. At the class level, Gammaproteobacteria had the highest abundance, with 453 isolates (86.1% of the total isolates). At the genus level, Vibrio had the highest abundance, with 369 isolates (70.2%). At the species level, V. alginolyticus was the most dominant species, with 112 isolates (21.3%). V. alginolyticus was distributed in the whole breeding system and had the highest abundance in the baits. The multiple correlation analysis showed that the influence of baits on the structure of culturable bacterial community increased gradually with the development of larvae. The MLSA confirmed 100 out of the 112 potential isolates as V. alginolyticus. MLSA was further employed to construct a phylogenetic tree for revealing the genetic diversity of the isolates. The 100 V. alginolyticus isolates were classified into 9 clusters, and the isolates from the same type of samples showed dispersed distribution in different clusters. [Conclusion] During the occurrence of BVS, abundant culturable microorganisms existed in the factory breeding system of L. vannamei. The baits exerted effect on the structure of culturable bacterial community in the larvae. V. alginolyticus was the dominant species of Vibrio in the factory breeding system of L. vannamei, with wide distribution and high genetic diversity in the breeding system. The results of this study provide data support for analyzing the succession rules of culturable microorganisms in shrimp breeding system and lays a foundation for pathogen prevention and control and healthy breeding of shrimp.
