Interaction between live seaweed and various Vibrio species by co-culture: Antibacterial activity and seaweed microenvironment

The antibacterial activity of live seaweed (Ulva fasciata, Gracilaria blodgettii and Pelvetia siliguosa) were examined on the three Vibrio (V.) strains (V. parahaemolyticus J1 and V. alginolyticus R1 from maricultural areas, a standard strain of V. parahaemolyticus ATCC17802). Three seaweed species all showed strong inhibition on the cultur-ability of Vibrio strains. Ulva (U.) fasciata as representative seaweed was further studied, which also exhibited inhibition on the swimming behavior, twitching behavior and biofilm formation of three strains. Much more up-regulated differentially expressed genes (DEGs) of U. fasciata occurred in response to V. alginolyticus (5213) than those to both two strains V. parahaemolyticus (3860, 4167), and more than 90% DEGs related to the biosynthesis of secondary metabolites (SMs) were all up-regulated (128-161 DEGs), the least of which and their related pathways occurred by the stress of the standard strain. The stress of two strains from mariculture areas caused richer and more similar profile of up-regulated DEGs in the 30-36 types of SMs biosynthesis pathways, especially for ubiquinone and other terpenoid-quinone biosynthesis with five more up-regulated DEGs than those by the stress of the standard strain. However, the most up-regulated DEGs in the pathways of biosynthesis of unsatu-rated fatty acids and steroid biosynthesis occurred under the stress of the standard strain and V. alginolyticus, respectively. In addition, Vibrio strains largely promoted the enrichment of endophytic bacteria (EB), mainly for phylum Proteobacteria and genera Alteromonas, Fretibacter, Ruegeria, etc., which favored the U. fasciata against Vibrio. The more significant variation of EB community was also caused by the Vibrio stress isolated from mariculture areas than that by standard strain.