Disentangling the abundance and structure of Vibrio communities in a semi-enclosed Bay with mariculture (Dongshan Bay, Southern China)

The genus Vibrio contains a diverse group of heterotrophic bacteria, which are members of ubiquitous and abundant microbial communities in coastal ecosystems. Vibrio has been frequently found in a wide range of marine environments either by employing Vibrio-specific 16S rRNA sequencing or culturing methods. A combination of molecular and cultivation-dependent methods was developed to more precisely discriminate between different members of the genus Vibrio in seawater. This newly developed assay was subsequently applied to characterize Vibrio community composition in surface water at 18 mariculture sites. It Substantially improved the taxonomic resolution of Vibrio species when compared to traditional 16S rRNA analysis. Our qPCR and cultivation analyses revealed that average Vibrio abundance (Vibrio 16S rRNA gene copy numbers: 3.46 × 10⁶ to 6.70 × 10⁶ copies L^-1) and live cell numbers (5.65 × 10⁴-5.75 × 10⁵ cfu mL^-1) are significantly related to pH. Total bacteria and Vibrio-specific 16S rRNA metabarcode sequenceing resulted in a total of 10 and 32 operational taxonomic units (OTUs), respectively, and 15 Vibrio species were identified by targeted cultivation of Vibrio strains, with Vibrio fortis and V. brasiliensis dominating in the mariculture areas. The purpose of this study was to combine several analytical methods to improve current sequence-based Vibrio community surveys, and to prove for the effectiveness of this methodological approach comprehensively testing for Vibrio dynamics in different coastal environments.