INCLUSION OF AEROMONAS DNA HYBRIDIZATION GROUP-11 IN AEROMONAS-ENCHELEIA AND EXTENDED DESCRIPTIONS OF THE SPECIES AEROMONAS-EUCRENOPHILA AND A-ENCHELEIA

The recently reported chemotaxonomic and genotypic description of two well-separated subgroups (I and II) in Aeromonas eucrenophila and thei r affiliation to Aeromonas encheleia and the unnamed Aeromonas DNA hyb ridization group (HG) 11 (G. Huys, M. Altwegg, M.-L. Hanninen, M. Vanc anneyt, L. Vauterin, R. Coopman, U. Torck, J. Luthy-Hottenstein, P. Ja nssen, and K. Kersters, Syst. Appl. Microbiol. 19:616-623, 1996) has q uestioned the original species descriptions of A. eucrenophila and A. encheleia. In order to elucidate the unclear taxonomic status of these taxa in the genus Aeromonas, we have further investigated a collectio n of 14 reference strains and 14 related isolates encompassing the tax a A. eucrenophila subgroups I and II, A. encheleia, and HG11 by DNA-DN A hybridization (on 17 of the 28 strains) and phenotypic characterizat ion (on all 28 strains). Genotypically, the investigated strains could be grouped into two DNA hybridization groups that exhibited between-g roup homologies ranging from 42 to 52%. The members of DNA homology gr oup I (DNA binding, 76 to 100%) were strains of A. eucrenophila subgro up I, including the type strain LMG 3774, and two A. eucrenophila-like isolates, leading to the conclusion that these strains should be cons idered true representatives of the species A. eucrenophila. The strain s of A. eucrenophila subgroup II, HG11, and A. encheleia, on the other hand, were closely joined in DNA homology group II (DNA binding, 74 t o 105%) together with two presumptive A. encheleia isolates. The fact that strain LMG 16330(T) of A. encheleia was the only type strain resi ding in DNA homology group II implies that HG11 and A. eucrenophila su bgroup II should be classified in the species A. encheleia. Except for the somewhat aberrant phenotypic positions of HG11 strains LMG 13075 and LMG 13076, the establishment of DNA homology groups I and II was s upported by the delineation of phena 1 and 2 (level of correlation, 90 %), respectively, as revealed by numerical analysis of 136 phenotypic test results. These data indicate that A. eucrenophila and A. enchelei a are phenotypically highly related but can be easily separated by tes ting the production of acid from D-cellobiose and lactose and the assi milation of D-cellobiose. Extended descriptions of both species are gi ven.