The genus Shewanella has been studied since 1931 with regard t o a variety of topics of relevance t o both applied and environmental microbiology. Recent years have seen the introduction of a large number of new Shewanella-like isolates, necessitating a coordinated review of the genus. In this work, the phylogenetic relationships among known shewanellae were examined using a battery of morphological, physiological, molecular and chemotaxonomic characterizations. This polyphasic taxonomy takes into account all available phenotypic and genotypic data and integrates them into a consensus classification. 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 halophilicity. Fatty acid and quinone profiling were used t o impart an additional layer of information. Molecular characterizations employing smallsubunit 16s rDNA sequences were at the limits of resolution for the differentiation of species in some cases. As a result, DNA-DNA hybridization and sequence analyses of a more rapidly evolving molecule (gyrB gene) were performed. Species-specif ic PCR probes were designed for the gyrB gene and used for the rapid screening of closely related strains. With this polyphasic approach, in addition t o the ten described Shewanella species, two new species, Shewanella oneidensis and ' Shewanella pealeana', were recognized; Shewanella oneidensis sp. nov. is described here for the first time.

No abstract

Microbial communities within deep subsurface environments were analyzed by 16S rRNA gene cloning. Clone libraries from 27 borehole fluid, 7 mining-contaminated, and 5 rock samples were compared. Borehole fluids derived from deep fractures were populated by microbial communities with low diversity with an average of 11 and 5 bacterial and archaeal OTUs respectively. Low taxa richness was likely driven by limited biogeochemical reactions available for growth and not extreme parameters such as pH and tempera-

No abstract

A new bacterial species belonging t o the genus Shewanella is described on the basis of phenotypic characterization and sequence analysis of its 165 rRNAencoding and gyrase B (gyrB) genes. This organism, isolated from shallowwater marine sediments derived from the Amazon River delta, is a Gramnegative, motile, polarly flagellated, facultatively anaerobic, rod-shaped eubacterium and has a G+C content of 51.7 mol0/o. Strain SB2BT is exceptionally active in the anaerobic reduction of iron, manganese and sulfur compounds. SB2BT grows optimally at 35 "C, with 1-3% NaCl and over a pH range of 7-8. Analysis of the 165 rDNA sequence revealed a clear affiliation between strain SB2BT and members of the gamma subclass of the class Proteobacteria. High similarity values were found with certain members of the genus Shewanella, especially with Shewanella putrefaciens, and this was supported by cellular fatty acid profiles and phenotypic characterization. DNA-DNA hybridization between strain SB2BT and its phylogenetically closest relatives revealed low similarity values (246-4207 %) which indicated species status for strain SB2BT. That SB2BT represents a distinct bacterial species within the genus Shewanella is also supported by gyrB sequence analysis. Considering the source of the isolate, the name Shewanella amazonensis sp. nov. is proposed and strain SB2BT (= ATCC 7003293 is designated as the type strain.

No abstract

No abstract

Lacustrine ferromanganese oxide nodules have been discovered in Lake Vermilion, northern Minnesota, USA. They occur as two morphotypes: laminated discs growing around or on cobbles ("reef-type"), and ovoid nodules on muddy gravel ("oncoidtype"). Nodules have only been found within a depth-range of »1 to 7 m, and no nodules were found on or in ne mud sediments. Oxide coatings on recent litter allowed estimates of growth rates between 2.3 to 3.5 ¹m/yr. X-ray diffraction, energy dispersive X-ray spectroscopy, and thin section and environmental scanning electron microscopy of the nodules showed microorganisms, chie y bacteria but also including cyanobacteria, diatoms, and other protozoans, mineralized by X-ray amorphous ferromanganese oxyhydroxide compounds and forming porous granular layers. ESEM examination also revealed solid-appearing layers, with no microorganism remains. Bacterial culturing experiments were carried out using lake water, sediment, and nodule swabs and pieces as the inocula. All resulted in the growth of bacteria that reduce and/or oxidize iron and manganese, showing that metal oxidizing and reducing bacteria are ubiquitous within the lake habitats. The culturing experiments also demonstrate that the bacteria can cause the formation of solid metal oxides. The combination of culturing and ESEM