Motility, biofilm formation and associated gene expression in Vibrio parahaemolyticus impaired by co-culture with live Ulva fasciata.

Aims Vibrio (V.) parahaemolyticus is one of the most frequently occurred pathogens in mariculture. This study aimed to explore the mechanism of the impact of Ulva fasciata (U. fasciata) on the motility and biofilm formation of V. parahaemolyticus. Methods and results The inhibitory effect of U. fasciata on a V. parahaemolyticus, isolated from clam maricultural sediment, was examined by co-culture. The live U. fasciata significantly inhibited the swimming behaviour, twitching behaviour and biofilm formation of V. parahaemolyticus JF, with inhibition rates ranging from 2.48%-20.26%, 1.59-39.18%, and 28.3-94.7% under different nitrate and phosphate levels. The results of transcriptome sequencing showed that 210 significantly differentially expressed genes were found in strain JF between the presence and absence of U. fasciata, including 90 upregulated genes and 120 downregulated genes. According to GO (Gene Ontology) function enrichment and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis, the downregulated genes of JF were partially enriched in flagella assembly (fliC, fliK, fliG, fliN, fliH, fliI, fliJ, fliA), bacterial chemotaxis (mCP, cheB, cheW, cheY) and biofilm formation (fliA/σ28 , eps), which explained the suppressed motility and biofilm formation of V. parahaemolyticus JF under U. fasciata stress. Conclusions Live U. fasciata significantly impaired the motility and biofilm formation of V. parahaemolyticus, which could occur in niches with either sufficient or inadequate nutrient (nitrate and phosphate) concentrations. The differentially expressed genes of V. parahaemolyticus modulated by U. fasciata were enriched mainly in the flagellar assembly, bacterial chemotaxis and biofilm pathways. Significance and impact of study New information on how V. parahaemolyticus respond to U. fasciata regarding motility and adhesion behaviours, and the mechanism of that was firstly explored in this study. The results suggested that the seaweed U. fasciata has promising prospects as an environmentally friendly preventive measure to treat vibriosis in mariculture.