Characterization of the Potential Probiotic Vibrio sp. V33 Antagonizing Vibrio Splendidus Based on Iron Competition

Background：Vibrio splendidusVs is an important aquaculture pathogen that can infect a broad host of marine organisms. In our previous study, an antagonistic bacterium Vibrio sp. V33 that possessed inhibitory effects on the growth and virulence of a pathogenic isolate V.splendidusVs was identified. Objectives: Here, we further explored the antagonistic substances and antagonistic effects from the viewpoint of iron competition. Materials and Methods: The main antagonistic substances in the supernatants from Vibrio sp. V33 were identified using the bioassay-guided method. The response of V. splendidus Vs under the challenge of cell-free supernatant from Vibrio sp. V33 was determined via sodium dodecyl sulfate-polyacrylamide gel electrophoresis and real-time reverse-transcription PCR. Results: The main antagonistic substances produced by Vibrio sp. V33 have low molecular weights, are water soluble, and are heat-stable substances. Meanwhile, the iron uptake rate of Vibrio sp. V33 was higher than that of V. splendidus Vs. In the presence of cell-free supernatant from Vibrio sp. V33, expressions of two functional genes, viuB and asbJ related to ferric uptake processes in V. splendidus Vs, were up-regulated, whereas furVs coding the ferric uptake repressor was suppressed below 0.5-fold. One gene coding phosphopyruvate hydratase does not change at mRNA level, but was up-regulated at protein level. Conclusions: Our results suggested that antagonistic effect of Vibrio sp. V33 on the pathogenic isolate V.splendidusVs was partially due to the stronger ability of Vibrio sp. V33 to seize iron. This cell-free supernatant from Vibrio sp. V33 created an iron-limited milieu for V. splendidusVs, which led to the changed expression profiles of genes that were related to iron uptake in V. splendidusVs.