Abstract
The most important bacterial pathology currently occurring in Chilean freshwater salmon farming is the cold-water disease produced by the psychrotrophic bacteria Flavobacterium psychrophilum. The main aim of this study was to characterize the inhibitory activity of an antagonist strain on the formation of biofilms of a F. psychrophilum strain. The antagonistic strain Pseudomonas fluorescens FF48 was isolated from the sediment beneath the salmon cages of a freshwater Chilean salmon farm and was identified by using the 16S rRNA gene sequence analysis. The production of siderophores, mainly during the stationary phase of growth of the antagonist strain was demonstrated using the Chrome Azurol S method and through F. psychrophilum inhibition under iron saturation conditions. Subsequently, the effect of the antagonist supernatant on the formation of F. psychrophilum biofilm was tested using the crystal violet staining method observing an inhibition of the growth of F. psychrophilum, but no effect was observed when iron saturation concentrations were used. Furthermore, when the antagonist strain was previously deposited on the support, it completely inhibited the formation of F. psychrophilum biofilms, but when both bacteria were inoculated simultaneously no inhibitory effect was detected. In conclusion, it was demonstrated that FF48 strain is able to inhibit the formation of F. psychrophilum biofilms in vitro probably mediated by the siderophore production, suggesting its potential use as a biocontrol biofilm in freshwater fish rearing systems to prevent the persistence of biofilms of the fish pathogenic species F. psychrophilum.
Highlights
Flavobacterium psychrophilum is a widely distributed Gram negative bacterium, considered one of the most important pathogens affecting salmonid farms worldwide producing a severe negative impact on this industry due to the high fish mortality rate caused by this pathogen and the costs associated with its chemical treatment (Nilsen et al 2011)
To relate the Maximum inhibitory dilution (MID) values to the activity of the supernatant, it was assumed that the greater the inhibitory dilution of the supernatant, the greater would be its inhibitory activity on F. psychrophilum in a determined time
It was observed that the inhibitory activity of FF48 strain was only observed after 30 h of growth, increasing sharply entering stationary growth phase and remaining constant along the late-stationary phase, suggesting that the inhibitor compound is mainly produced during the stationary phase (Figure 1)
Summary
Flavobacterium psychrophilum is a widely distributed Gram negative bacterium, considered one of the most important pathogens affecting salmonid farms worldwide producing a severe negative impact on this industry due to the high fish mortality rate caused by this pathogen and the costs associated with its chemical treatment (Nilsen et al 2011). Antagonistic interactions between species have been studied principally in the planktonic phase (Robertson et al 2000; Kei et al 2006; Ström-Bestor and Wiklund 2011), species of microbes included in biofilms can interact in various ways with other species within the same biofilm (Moons et al 2009). These interactions start to influence a biofilm during the initial stages of its formation, adherence of the bacteria to the surface and colonization, and continue to influence the structure and physiology of the biofilm as it develops. It is believed that these interactions may be even more important in biofilms than in the planktonic state, because cell positions are relatively stable, and local areas of the biofilm which hinder molecular diffusion (James et al 1995; Eberl and Collinson 2009)
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