Abstract
Chemical analyses and mass spectrometry were used to study the structure of the lipopolysaccharide (LPS) isolated from Aeromonas bestiarum strain K296, serotype O18. ESI-MS revealed that the most abundant A. bestiarum LPS glycoforms have a hexa-acylated or tetra-acylated lipid A with conserved architecture of the backbone, consisting of a 1,4′-bisphosphorylated β-(1→6)-linked d-GlcN disaccharide with an AraN residue as a non-stoichiometric substituent and a core oligosaccharide composed of Kdo1Hep6Hex1HexN1P1. 1D and 2D NMR spectroscopy revealed that the O-specific polysaccharide (OPS) of A. bestiarum K296 consists of a branched tetrasaccharide repeating unit containing two 6-deoxy-l-talose (6dTalp), one Manp and one GalpNAc residues; thus, it is similar to that of the OPS of A. hydrophila AH-3 (serotype O34) in both the sugar composition and the glycosylation pattern. Moreover, 3-substituted 6dTalp was 2-O-acetylated and additional O-acetyl groups were identified at O-2 and O-4 (or O-3) positions of the terminal 6dTalp. Western blots with polyclonal rabbit sera showed that serotypes O18 and O34 share some epitopes in the LPS. The very weak reaction of the anti-O34 serum with the O-deacylated LPS of A. bestiarum K296 might have been due to the different O-acetylation pattern of the terminal 6dTalp. The latter suggestion was further confirmed by NMR.
Highlights
Aeromonas spp. bacteria are ubiquitous in various aquatic ecosystems, such as sea water, freshwater, estuarine and coastal waters, and are even found in chlorinated potable water
It was found that the LPS was distributed between the phenol and water phases as hydrophobic and hydrophilic LPS fractions in yields of 1.6% and 2.5% of the dry bacterial cell mass, respectively
The yield of the LPS extracted from the phenol, which was less than half of the yield obtained from the water indicated a lower content of LPS molecules substituted with O-specific polysaccharide (OPS) in the cell envelope of A. bestiarum K296
Summary
Aeromonas spp. bacteria are ubiquitous in various aquatic ecosystems, such as sea water, freshwater, estuarine and coastal waters, and are even found in chlorinated potable water They occur commonly in soil habitats and are frequently isolated from raw and processed food. The species Aeromonas hydrophila, Aeromonas salmonicida, Aeromonas caviae, Aeromonas veronii, Aeromonas sobria and Aeromonas bestiarum have been described as important fish pathogens. They cause chronic disease with skin ulceration or acute systemic infection, referred to as motile aeromonad septicemia (MAS), as well as other pathological lesions [5,6,7]. O18, which was isolated from pathologically altered tissue of carp (Cyprinus carpio L.) [24]
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