A new obligately chemolithoautotrophic, nitrite-oxidizing bacterium,Nitrospira moscoviensis sp. nov. and its phylogenetic relationship
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A gram-negative, non-motile, non-marine, nitrite-oxidizing bacterium was isolated from an enrichment culture initiated with a sample from a partially corroded area of an iron pipe of a heating system in Moscow, Russia. The cells were 0.9–2.2 μm×0.2–0.4 μm in size. They were helical- to vibroid-shaped and often formed spirals with up to three turns 0.8–1.0 μm in width. The organism possessed an enlarged periplasmic space and lacked intracytoplasmic membranes and carboxysomes. The cells tended to excrete extracellular polymers, forming aggregates. The bacterium grew optimally at 39°C and pH 7.6–8.0 in a mineral medium with nitrite as sole energy source and carbon dioxide as sole carbon source. The optimal nitrite concentration was 0.35 mM. Nitrite was oxidized to nitrate stoichiometrically. The doubling time was 12 h in a mineral medium with 7.5 mM nitrite. The cell yield was low; only 0.9 mg protein/l was formed during oxidation of 7.5 mM nitrite. Under anoxic conditions, hydrogen was used as electron donor with nitrate as electron acceptor. Organic matter (yeast extract, meat extract, peptone) supported neither mixotrophic nor heterotrophic growth. At concentrations as low as 0.75 g organic matter/l or higher, growth of nitrite-oxidizing cells was inhibited. The cells contained cytochromes of theb- andc-type. The G+C content of DNA was 56.9±0.4 mol%. The chemolithoautotrophic nitrite-oxidizer differed from the terrestrial members of the genusNitrobacter with regard to morphology and substrate range and equaledNitrospira marina in both characteristics. The isolated bacterium is designated as a new species of the genusNitrospira. Comparative analysis of 16S rRNA gene sequences revealed a moderate phylogenetic relationship toNitrospira marina, leptospirilla,Thermodesulfovibrio yellowstonii, “Magnetobacterium bavaricum”, and the isolate OPI-2. Initial evidence is given that these organisms represent a new phylum of the domain bacteria.
Key wordsNitrospira moscoviensis Non-marine bacteria Obligate chemolithoautotroph Nitrite oxidation Nitrate reduction 16S rRNA gene sequences
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