Aeromonas strains which phenotypically and genetically belong to the Aeromonas salmonicida species but that according to their phenotypic properties constitute a new subspecies have been isolated from the water of a heavily polluted river, the Matanza river, situated near the central district of Buenos Aires city. These strains were ascribed to the A. salmonicida species by using 65 biochemical tests and by DNA-DNA hybridization. They produce acid from -sorbitol, an unusual biochemical property found in a few members of the A. salmonicida species. They also utilize urocanic acid and do not ferment L-rhamnose or utilize LD-lactate, and are elastase- and gluconate-negative. The DNA relatedness was over 70%, the current limit accepted for the phylogenetic definition of a species, to the described A. salmonicida subspecies and nearly 100% within the new group of Aeromonas strains. Phenotypic differentiation from other A. salmonicida subspecies was readily achieved using the following characteristics: growth at 37 degrees C, melanin production, indole and Voges-Proskauer assays, growth on KCN broth, mannitol and sucrose fermentation and gas from glucose. A remarkable property of the strains of the new group was their ability to degrade polypectate, an unusual feature among Aeromonas species in general. The complete 16S rRNA gene of one strain of the new group was sequenced. Comparison with rDNA sequences of Aeromonas members available in databases revealed a close relationship between this strain and strains belonging to A. salmonicida subsp. salmonicida, masoucida and achromogenes, in agreement with the biochemical data. Since the new A. salmonicida strains constitute a tight genomic group that can be identified by phenotypic properties it was concluded that they represent a new subspecies for which the name Aeromonas salmonicida subsp. pectinolytica is proposed. The type strain of A. salmonicida subsp. pectinolytica is 34melT (= DSM 12609T).


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