Document Type : Research Paper
School of Marine Sciences, Ningbo University, Ningbo 315211, P.R. China.
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.