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Cultivated Beggiatoa spp. define the phylogenetic root of morphologically diverse, noncultured, vacuolate sulfur bacteria

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Within the last 10 years, numerous SSU rRNA sequences have been collected from natural populations of conspicuous, vacuolate, colorless sulfur bacteria, which form a phylogenetically cohesive cluster (large-vacuolate sulfur bacteria clade) in the -Proteobacteria. Currently, this clade is composed of four named or de facto genera: all known Thioploca and Thiomargarita strains, all vacuolate Beggiatoa strains, and several strains of vacuolate, attached filaments, which bear a superficial similarity to Thiothrix. Some of these vacuolate bacteria accumulate nitrate for respiratory purposes. This clade encompasses the largest known prokaryotic cells (Thiomargarita namibiensis) and several strains that are important in the global marine sulfur cycle. Here, we report additional sequences from five pure culture strains of Beggiatoa spp., including the only two cultured marine strains (nonvacuolate), which firmly establish the root of this vacuolate clade. Each of several diverse metabolic motifs, including obligate and facultative chemolithoautotrophy, probable mixotrophy, and seemingly strict organoheterotrophy, is represented in at least one of the nonvacuolate strains that root the vacuolate clade. Because the genus designation Beggiatoa is interspersed throughout the vacuolate clade along with other recognized or de facto genera, the need for taxonomic revision is clear.Key words: vacuolate, sulfur bacteria, Beggiatoa, 16S rDNA, phylogeny.

À l'intérieur des 10 dernières années, de nombreuses séquences d'ARNr SSU ont été recueillies de populations naturelles de bactéries sulfureuses apparentes, vacuolées et incolores qui forment un regroupement phylogénétiquement cohésif (clade des grandes bactéries sulfureuses vacuolées) dans la subdivision  des protéobactéries. Ce clade est présentement composé de trois genres nommés ou de facto, c'est-à-dire toutes les souches connues de Thioploca et Thiomargarita, tous les Beggiatoa vacuolées et plusieurs souches des filaments vacuolés attachés qui présentent une similitude superficielle à Thiothrix. Certaines de ces bactéries vacuolées accumulent le nitrate pour des besoins respiratoires. Ce clade englobe les plus grandes cellules procaryotes connues (Thiomargarita namibiensis) et plusieurs souches qui sont importantes dans le cycle du soufre marin global. Nous faisons ici le rapport de séquence additionnelle de cinq souches de cultures pures de Beggiatoa spp., incluant les deux seules souches marine cultivées (non vacuolées), qui établissent fermement les racines de ce clade vacuolé. Chacun des nombreux motifs métaboliques diversifiés, incluant la chemolithoautotrophie obligatoire ou facultative, la mixotrophie probable et une organohétérotrophie apparemment stricte, est représenté dans au moins une des souches non vacuolées qui forment la racine du clade vacuolé. Puisque cette désignation du genre Beggiatoa est dispersée à travers le clade vacuolé en compagnie d'autres genres reconnus ou de facto, il est clair qu'une révision taxonomique est requise.Mots clés : vacuolé, bactéries sulfureuses, Beggiatoa, ADNr 16S, phylogénie.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: June 1, 2006

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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