New Structure of Aeromonas salmonicida O-Polysaccharide Isolated from Ill Farmed Fish

Abstract

The diversity of O-polysaccharides (O-antigens) among 28 Aeromonas salmonicida strains isolated from ill fish has been determined by using high-resolution magic angle spinning (HR MAS) NMR spectroscopy. The new O-polysaccharide has been identified in two isolates. This new structure was investigated by ¹H and ¹³C NMR spectroscopy and matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The following structure of the linear hexasaccharide repeating unit of A. salmonicida O-antigen has been established: →3)-α-L-Rhap-(1→3)-α-D-ManpNAc-(1→2)-β-D-Glcp-(1→3)-α-L-Rhap2OAc4OAc-(1→3)-β-D-ManpNAc-(1→3)-α-D-Glcp-(1→. This new A. salmonicida O-polysaccharide was detected among two isolates collected from trout and turbot fish in 2010 and 2011, respectively. Further investigations should be conducted to evaluate the distribution of this new O-polysaccharide among a larger collection of isolates, depending on their geographic origin, the species of fish, and the health status of the fish.

Keywords: Aeromonas salmonicida; HR MAS NMR; O-polysaccharide diversity; lipopolysaccharide.

Figure 1

¹H HR MAS NMR spectra of A. salmonicida O-polysaccharides: (A) strain 11/A/658 with the new O-polysaccharide structure, (B) strain 9/A/632 with the structure B, and (C) strain 8/A/626 with the structure A. Chart represents A, B, C structures of A. salmonicida O-polysaccharides which have been identified [6]. * impurities from the microextraction step.

Figure 2

(A–C) Selected regions of ¹J_H,C- and ³J_H,C-connectivities in ¹H-¹³C HSQC-DEPT spectrum of the A. salmonicida 11/A/658 O-polysaccharide. The cross-peaks are marked as uppercase letters indicated in the text.

Figure 3

Selected region of the ¹H-¹H NOESY spectrum of the A. salmonicida 11/A/658 O-polysaccharide (PSI fraction).

Figure 4

MALDI-TOF MS spectrum of the A. salmonicida 11/A/658 O-polysaccharide (PSI fraction).