A NEW OBLIGATELY CHEMOLITHOAUTOTROPHIC, NITRITE-OXIDIZING BACTERIUM, NITROSPIRA-MOSCOVIENSIS SP-NOV AND ITS PHYLOGENETIC RELATIONSHIP

A gram-negative, non-motile, non-marine, nitrite-oxidizing bacterium w as 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 mu m x 0.2-0.4 mu m in size. They were helical- to vibroid-shaped and often formed spirals with up to three turns 0.8-1.0 mu m in width. The organism possessed an enlarged peripl asmic space and lacked intracytoplasmic membranes and carboxysomes. Th e cells tended to excrete extracellular polymers, forming aggregates. The bacterium grew optimally at 39 degrees C and pK 7.6-8.0 in a miner al medium with nitrite as sole energy source and carbon dioxide as sol e carbon source. The optimal ni trite concentration was 0.35 mM. Nitri te was oxidized to nitrate stoichiometrically. The doubling time was 1 2 h in a mineral medium with 7.5 mM nitrite. The cell yield was low; o nly 0.9 mg protein/l was formed during oxidation of 7.5 mM nitrite. Un der anoxic conditions, hydrogen was used as electron donor with nitrat e as electron acceptor. Organic matter (yeast extract, meat extract, p eptone) supported neither mixotrophic nor heterotrophic growth. At con centrations as low as 0.75 g organic matter/l or higher, growth of nit rite-oxidizing cells was inhibited. The cells contained cytochromes of the b- and c-type. The G+C content of DNA was 56.9 +/- 0.4 mol%. The chemolithoautotrophic nitrite-oxidizer differed from the terrestrial m embers of the genus Nitrobacter with regard to morphology and substrat e range and equaled Nitrospira marina in both characteristics. The iso lated bacterium is designated as a new species of the genus Nitrospira . Comparative analysis of 16S rRNA gene sequences revealed a moderate phylogenetic relationship to Nitrospira marina, leptospirilla, Thermod esulfovibrio yellowstonii, ''Magneto-bactrium bavaricum,'' and the iso late OPI-2. Initial evidence is given that these organisms represent a new phylum of the domain bacteria.