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 Vibrio parahaemolyticus YDE17 pathogenic to shrimp and its antagonist Glutamicibacter sp. ZY1 were screened, and ZY1 showed stable inhibitory effects on diverse Vibrio spp., especially V. parahaemolyticus. 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 in vivo 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 Vibrio spp.
Ningning Liu,Shanshan Zhang,Weiwei Zhang,Chenghua Li
Recently, the use of probiotics as an alternative strategy to control bacterial diseases in aquaculture has garnered much attention due to the merits of environmental friendliness. In this study, a bacterium identified as Vibrio sp. V33 was isolated from healthy sepia and was determined to have strong antagonistic activity towards the pathogenic isolate Vibrio splendidus Vs using the disk diffusion method. The antagonistic substance was secreted into the supernatant and was thermo-stable. The antagonistic activity of Vibrio sp. V33 may be attributed to its higher ability to compete for iron than that of V . splendidus Vs, as deduced from siderophore quantification using the CAS method. Number of colony counts from seawater and Apostichopus japonicus infection experiments showed that Vibrio sp. V33 significantly decreased the quantity of V . splendidus Vs in natural seawater and promoted the survival rate of A . japonicus infected by V . splendidus , with a relative percentage survival of 43% under the current conditions. Our findings suggest that V33 could be potentially used as potential bacterial antagonist for controlling V . splendidus infections in sea cucumber aquaculture. Statement of relevance It might protect A . japonicus from V . splendidus infection.
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