Aeromonas salmonicida subsp pectinolytica subsp nov., a new pectinase-positive subspecies isolated from a heavily polluted river

Aeromonas strains which phenotypically and genetically belong to the Aeromo nas salmonicida species but that according to their phenotypic properties c onstitute a new subspecies have been isolated from the water of a heavily p olluted river, the Matanza river, situated near the central district of Bue nos Aires city. These strains were ascribed to the A. salmonicida species b y using 65 biochemical tests and by DNA-DNA hybridization. They produce aci d from D-sorbitol, an unusual biochemicsll property found in a few members of the A. salmonicida species. They also utilize urocanic acid and do not f erment L-rhamnose or utilize LD-lactate, and are elastase- and gluconate-ne gative. The DNA relatedness was over 70%, the current limit accepted for th e phylogenetic definition of a species, to the described A. salmonicida sub species and nearly 100% within the new group of Aeromonas strains. Phenotyp ic differentiation from other A. salmonicida subspecies was readily achieve d using the following characteristics: growth at 37 degrees C, melanin prod uction, indole and Voges-Proskauer assays, growth on KCN broth, mannitol an d sucrose fermentation and gas from glucose. A remarkable property of the s trains of the new group was their ability to degrade polypectate, an unusua l 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 b etween this strain and strains belonging to A. salmonicida subsp. salmonici da, masoucida and achromogenes, in agreement with the biochemical data. Sin ce the new A. salmonicida strains constitute a tight genomic group that can be identified by phenotypic properties it was concluded that they represen t a new subspecies for which the name Aeromonas salmonicida subsp. pectinol ytica is proposed. The type strain of A. salmonicida subsp. pectinolytica i s 34mel(T) (= DSM 12609(T)).