Seasonal dynamics of microbial communities and potential human pathogens in Crassostrea hongkongensis and ambient water in southern China.

UNLABELLED: Oysters are a popular raw seafood worldwide, yet their contamination with human pathogens poses substantial public health risks. However, the seasonal dynamics of host-associated microbiota and the environmental drivers of pathogen accumulation in Crassostrea hongkongensis remain poorly understood. Here, we conducted 16S rRNA amplicon sequencing to profile the gill and intestinal microbiota of C. hongkongensis, sampled quarterly over a 1-year period in Beihai and Zhanjiang, southern China. A pronounced divergence in oyster-associated bacterial communities was observed between the two locations in December. Key bacterial families, such as Lachnospiraceae and Muribaculaceae, showed significant temporal fluctuations in abundance, suggesting their potential role in maintaining bacterial community stability within oysters. These microbial shifts were significantly correlated with environmental parameters such as chlorophyll a and pH. In parallel, we used plate counting to quantify five foodborne pathogens and total viable counts. Vibrios were more frequently detected in oyster tissues than in ambient seawater. Pathogen-associated amplicon sequence variants exhibited a strong response to variations in pH and chlorophyll a, whereas the abundance of culturable Vibrio vulnificus was significantly negatively correlated with temperature and nitrate. The integration of high-throughput sequencing and culture-based methods provides comprehensive insights into the dynamics of pathogenic bacteria within oysters under natural mariculture settings. This study offers valuable ecological insights into the interactions within the oyster-associated microbial ecosystem, contributing to a deeper understanding of its dynamics and implications for public health. IMPORTANCE: Mariculture of Crassostrea hongkongensis serves as a critical interface between coastal ecology and public health, yet seasonal dynamics of its microbiome and core stabilizing taxa remain poorly understood in subtropical aquaculture. This study identified Acetobacteraceae, Lachnospiraceae, Prevotellaceae, and Muribaculaceae as key families associated with seasonal microbiome stability in C. hongkongensis, highlighting their potential contribution to community resilience. It further revealed that Vibrio species detection was negatively correlated with temperature. These findings advance our understanding of interactions between the oyster microbiome and the environment, and provide a theoretical basis for improving oyster health management and promoting sustainable aquaculture practices.