Polyphasic taxonomy of the genus Shewanella and description of Shewanella oneidensis sp. nov.

The genus Shewanella has been studied since 1931 with regard to a variety o f topics of relevance to both applied and environmental microbiology. Recen t years have seen the introduction of a large number of new Shewanella-like isolates, necessitating a coordinated review of the genus. In this work, t he phylogenetic relationships among known shewanellae were examined using a battery of morphological, physiological, molecular and chemotaxonomic char acterizations. This polyphasic taxonomy takes into account all available ph enotypic and genotypic data and integrates them into a consensus classifica tion, Based on information generated from this study and obtained from the literature, a scheme for the identification of Shewanella species has been compiled. Key phenotypic characteristics were sulfur reduction and halophil icity, Fatty acid and quinone profiling were used to impart an additional l ayer of information, Molecular characterizations employing small-subunit 16 S rDNA sequences were at the limits of resolution for the differentiation o f species in some cases. As a result, DNA-DNA hybridization and sequence an alyses of a more rapidly evolving molecule (gyrB gene) were performed. Spec ies-specific PCR probes were designed for the gyrB gene and used for the ra pid screening of closely related strains. With this polyphasic approach, in addition to the ten described Shewanella species, two new species, Shewane lla oneidensis and 'Shewanella pealeana', were recognized; Shewanella oneid ensis sp, nov. is described here for the first time.