Seasonal dynamics of host-associated microbiome and potential human pathogen in Crassostrea ariakensis and Perna...

The microbial communities and foodborne pathogenic bacteria in bivalves have long been topics of interest due to their fundamental economic and ecological roles. This study investigated the seasonal dynamics of microbial composition and foodborne pathogen loads in the gills and visceral mass of Crassostrea ariakensis and Perna viridis, cohabiting the same aquatic environment. Both bivalve species exhibited higher bacterial richness and diversity than the surrounding water. They shared 5682 ASVs, accounting for over 50% of total ASVs. Core microbiota in both species was dominated by Firmicutes and Proteobacteria, though P. viridis gills showed higher Spirochaetota abundance. At the family level, Lactobacillaceae and Acetobacteraceae were predominant in June but decreased markedly in other months. Spirochaetaceae relative abundance was consistently higher in P. viridis than in C. ariakensis. C. ariakensis exhibited a greater relative abundance of potential pathogens (up to 10.75%), primarily Escherichia-Shigella and Bacteroides, whereas P. viridis was dominated by Lactiplantibacillus and Escherichia-Shigella. Plate counting identified V. parahaemolyticus and V. vulnificus as the dominant culturable foodborne bacteria, with higher abundances in March and December. The visceral mass often harbored higher bacterial levels than gills. Potential pathogen profiles from 16S rRNA data were influenced by temperature, pH, chlorophyll-a, ammonia nitrogen, and phosphate, whereas total culturable bacteria were affected by all measured factors except chlorophyll-a. Temperature and nitrate significantly influenced V. vulnificus abundance in both bivalves. This study highlights how host species, tissue type, season, and environmental factors interact to shape bivalve-associated microbiomes and pathogen prevalence, providing insights for seafood safety management.