Screening and Characterization of a Bacterium Named 4-1-3 Antagonizing Aeromonas veronii

Abstract:

Aeromonas veronii is a highly mortal pathogenic microorganism in the loach aquaculture. To screen the antagonistic bacteria and to develop microbial preparation against the pathogens, the samples were collected from loach breeding pond and the bacteria strains were isolated and screened for the ability to inhibit the size of the zone of the strains. The active substances were separated and purified with the ammonium sulfate precipitation and ion exchange chromatography, and the molecular weights were revealed with the sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A strain named 4-1-3 was isolated and screened from the samples collected from the bottom sediments of a loach breeding pond in the Lianyungang city, and it identified as Pseudomonas fluorescens based on its morphology and the analysis of 16S rRNA gene sequence, designated as P. fluorescens 4-1-3. The strain strongly inhibited the growth of A. veronii, with 15.2 mm inhibition zone diameter. The antibacterial substance produced by the strain P. fluorescens 4-1-3 is an extracellular protein which can be precipitated using 60% ammonium sulfate and eluted by 600 mmol/L NaCl through Sepharose DEAE Fast Flow. The molecular weight of P. fluorescens 4-1-3 is around 100 kDa determined by SDS-PAGE. In this study, we obtained a strain that can inhibit the growth of A. veronii and we found a new bacteria antagonistic substance produced by P. fluorescens. The present study provides evidence to the improve disease control in loach breeding and other aquaculture.