Virulent and nonvirulent Flavobacterium columnare colony morphologies: characterization of chondroitin AC lyase activity and adhesion to polystyrene.

AIMS: Colony morphology variants of fish pathogenic Flavobacterium columnare were studied to clarify the role of colony morphology change in the virulence of the bacterium. Typical rhizoid colony (Rz) variants are virulent and moderately adherent, nonrhizoid rough (R) colony variants are nonvirulent and highly adherent, and soft colony (S) variants are nonvirulent and poorly adherent. METHODS AND RESULTS: Chondroitin AC lyase activity, adhesion to polystyrene at different temperatures and after modification of bacterial surface, and lipopolysaccharide (LPS) profiles of the variants were studied. The chondroitinase activity was significantly higher in the virulent, rhizoid variants than in the rough variants of the same strain. Temperature significantly increased the adhesion of rhizoid variants up to 20°C. Modification of bacterial surface suggested that adhesion molecules contain both carbohydrates and proteins. LPS did not differ between the variants of the same strain. CONCLUSIONS: The results suggest that in Fl. columnare both rhizoid colony morphology and high chondroitinase activity are needed for virulence and that temperature may promote the adhesion of the virulent variants to surfaces at fish farms. SIGNIFICANCE AND IMPACT OF THE STUDY: New information is produced on the virulence mechanisms of Fl. columnare and the reasons behind the survival of the bacterium at fish farms.

Vacuum Rabi splitting and strong-coupling dynamics for surface-plasmon polaritons and rhodamine 6G molecules.

We report on strong coupling between surface-plasmon polaritons (SPP) and Rhodamine 6G (R6G) molecules, with double vacuum Rabi splitting energies up to 230 and 110 meV. In addition, we demonstrate the emission of all three energy branches of the strongly coupled SPP-exciton hybrid system, revealing features of system dynamics that are not visible in conventional reflectometry. Finally, in analogy to tunable-Q microcavities, we show that the Rabi splitting can be controlled by adjusting the interaction time between waveguided SPPs and R6G deposited on top of the waveguide. The interaction time can be controlled with sub-fs precision by adjusting the length of the R6G area with standard lithography methods.

Molecular diversity and growth features of Flavobacterium columnare strains isolated in Finland.

Columnaris disease caused by Flavobacterium columnare is a problem in fish farming worldwide. During the last 15 yr, outbreaks have started to emerge in Finland. Flavobacterium columnare Type Strain NCIMB 2248T and 30 Finnish F. columnare isolates were studied using analysis of 16S rDNA by restriction-fragment length polymorphism (16S RFLP), length heterogeneity analysis of polymerase chain reaction (LH-PCR) products, automated ribosomal intergenic spacer analysis (ARISA), and 16S rDNA sequence analysis. All isolates fell into RFLP Genomovar I and had the same length in the LH-PCR analysis. Based on ARISA, 8 genetically different strains were selected for further analyses. The growth of these strains under different temperatures, NaCl concentrations, and pH values was tested. The Finnish F. columnare strains did not grow at NaCl concentrations >0.1% or at pH values < or = 6.5, and they were susceptible to several antimicrobial agents, but not to Polymyxin B or neomycin. These findings may aid in development of methods for disease management at fish farms.