Genotypic and chemotaxonomic description of two subgroups in the species Aeromonas eucrenophila and their affiliation to A-encheleia and Aeromonas DNA hybridization group 11

We describe the results of a polyphasic taxonomic study that aimed to elucidate the genotypic heterogeneity observed previously among the eight original reference strains of the species Aeromonas eucrenophila. In addition, this investigation also included representatives of the neighbouring taxa Aeromonas encheleia and Aeromonas DNA hybridization group (HG) 11, as well as a collection of 14 mainly aquatic Aeromonas sp. isolates which were previously found to be closely related to A. eucrenophila. All 28 strains were subjected to ribotyping, whole-genome analysis by AFLP fingerprinting, electrophoretic profiling of soluble cellular proteins, and gas-liquid chromatographic analysis of cellular fatty acid methyl eaters. Cluster analysis of the data uniformly confirmed our previous findings and delineated two well-separated subgroups in A. eucrenophila. Subgroup I was represented by the type strain of this species (LMG 3774) and four other original reference strains, of which one strain (LMG 13687) displayed a somewhat atypical fatty acid profile. This subgroup could be extended by the inclusion ai lour Aeromonas isolates that were unambiguously classified in A. eucrenophila subgroup I. The three remaining reference strains originally described as A. eucrenophila were allocated to subgroup II, but could not be differentiated from members of A. encheleia and HG11. Consequently, a clear-cut classification of poorly identified or unknown Aeronomas isolates into one of the latter three taxa was not possible on genotypic or chemotaxonomic basis. In conclusion, the current report has provided substantial polyphasic evidence to support an emended description of the species A. eucrenophila. Moreover, the high genotypic and chemotaxonomic resemblance of A. eucrenophila subgroup LI, HG11, and A. encheleia revealed in this study suggests that these three groups may actually belong to the same genomic species.