Abstract
Comparison between the lipopolysaccharide (LPS) core structures of Aeromonas salmonicida subsp. salmonicida A450 and Aeromonas hydrophila AH-3 shows great similarity in the inner LPS core and part of the outer LPS core but some differences in the distal part of the outer LPS core (residues ld-Hep, d-Gal, and d-GalNAc). The three genomic regions encoding LPS core biosynthetic genes in A. salmonicida A450, of which regions 2 and 3 have genes identical to those of A. hydrophila AH-3, were fully sequenced. A. salmonicida A450 region 1 showed seven genes: three identical to those of A. hydrophila AH-3, three similar but not identical to those of A. hydrophila AH-3, and one without any homology to any well-characterized gene. A. salmonicida A450 mutants with alterations in the genes that were not identical to those of A. hydrophila AH-3 were constructed, and their LPS core structures were fully elucidated. At the same time, all the A. salmonicida A450 genes identical to those of A. hydrophila AH-3 were used to complement the previously obtained A. hydrophila AH-3 mutants for each of these genes. Combining the gene sequence and complementation test data with the structural data and phenotypic characterization of the mutant LPSs enabled a presumptive assignment of all LPS core biosynthesis gene functions in A. salmonicida A450. Furthermore, hybridization studies with internal probes for the A. salmonicida-specific genes using different A. salmonicida strains (strains of different subspecies or atypical strains) showed a unique or prevalent LPS core type, which is the one fully characterized for A. salmonicida A450.