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

BACKGROUND

Vs is an important aquaculture pathogen that can infect a broad host of marine organisms. In our previous study, an antagonistic bacterium sp. V33 that possessed inhibitory effects on the growth and virulence of a pathogenic isolate Vs 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 sp. V33 were identified using the bioassay-guided method. The response of Vs under the challenge of cell-free supernatant from sp. V33 was determined via sodium dodecyl sulfate-polyacrylamide gel electrophoresis and real-time reverse-transcription PCR.

RESULTS

The main antagonistic substances produced by sp. V33 have low molecular weights, are water soluble, and are heat-stable substances. Meanwhile, the iron uptake rate of sp. V33 was higher than that of Vs. In the presence of cell-free supernatant from sp. V33, expressions of two functional genes, viuB and asbJ related to ferric uptake processes in 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 sp. V33 on the pathogenic isolate Vs was partially due to the stronger ability of sp. V33 to seize iron. This cell-free supernatant from sp. V33 created an iron-limited milieu for Vs, which led to the changed expression profiles of genes that were related to iron uptake in Vs.