<i>Glutamicibacter</i> sp. ZY1 antagonizes pathogenic <i>Vibrio parahaemolyticus</i> via iron competition

Probiotics are prior agents for treating bacterial infection with advantages of inhibiting pathogenic bacteria and improving immune responses of hosts, thus increasing the survival rate of cultured animals. In this study, one <i>Vibrio parahaemolyticus</i> YDE17 pathogenic to shrimp and its antagonist <i>Glutamicibacter</i> sp. ZY1 were screened, and ZY1 showed stable inhibitory effects on diverse <i>Vibrio</i> spp., especially <i>V. parahaemolyticus</i>. ZY1 secreted inhibitory substances into supernatant, and the activity of inhibitory substances did not change after being treated under different temperatures, proteinase K, and pH (6-10), which indicated that the inhibitory substances might be small molecules, which led us to trace the siderophore production. The siderophore production of YDE17 co-incubated with the cell-free supernatant of ZY1 was greater than that of YDE17 alone, which indicated that the cell-free supernatant of ZY1 created iron-limiting conditions for YDE17. This finding was confirmed by iron supplementation assays, in which the inhibitory activity of the cell-free supernatant of ZY1 on YDE17 as well as the siderophore production of YDE17 decreased in the presence of FeCl₃. The effect of iron on inhibition was further confirmed by <i>in vivo</i> infection. The relative percent survival of ZY1 to shrimp challenged by YDE17 was 83.3%, but the survival rates of shrimp challenged with YDE17/ZY1/FeCl₃ were similar to that of YDE17, both of which were significantly lower than the 70% survival rate of shrimps simultaneously challenged by ZY1/YDE17. Our study offers a new probiotic resource to control vibriosis, which works through iron competition with the opportunistic pathogens of <i>Vibrio</i> spp.IMPORTANCEBacteria belonging to <i>Vibrio</i> spp., especially <i>Vibrio parahaemolyticus</i>, are important opportunistic pathogens infecting a wide range of hosts including fish, shrimp, shellfish, and crab. Antibiotics are effective but show the disadvantages of antibiotic generation, microecology destruction, and biological toxicology; thus, new treatments of <i>Vibrio</i> infection are urgently recommended. In our present study, <i>Glutamicibacter</i> sp. ZY1, belonging to the phylum Actinomycetes, was selected and showed high inhibitory activity to inhibit <i>V. parahaemolyticus</i> pathogenic to shrimp. <i>Glutamicibacter</i> sp. ZY1 antagonized <i>V. parahaemolyticus</i> YDE17 through producing siderophore to compete for iron, based on the results of both <i>in vitro</i> and in <i>vivo</i> experiments under different iron levels. This study offers a new strategy to control <i>Vibrio</i> infection in aquaculture.