Here we report on the biodiversity and abundance of aerobic and anaerobic ammonium-oxidizing bacteria in sediment samples from the Xinyi River, Jinagsu Province (China). The biodiversity of aerobic ammonium-oxidizing bacteria in the sediment was assessed using the amoA gene as functional marker. The retrieved amoA clones were affiliated to environmental sequences from freshwater habitats. The closest cultivated relative was Nitrosomonas urea. Anaerobic ammonium-oxidizing (anammox) bacteria were studied using anammox and planctomycete-specific 16S rRNA gene primers. The sediments contained 16S rRNA genes and bacterial cells closely related to the known anammox bacterium Candidatus'Brocadia anammoxidans'. Anaerobic continuous flow reactors were set up to enrich anammox organisms from the sediments. After an adaptation period of about 25 days the reactors started to consume ammonium and nitrite, indicating that the anammox reaction was occurring with a rate of 41-58 nmol cm(-3) h(-1). Community analysis of the enrichments by quantitative fluorescence in situ hybridization showed an increase in the abundance of anammox bacteria from < 1% to 6 +/- 2% of the total population. Analysis of the 16S rRNA genes showed that the enriched anammox organisms were related to the Candidatus'Scalindua' genus.
shape, helical and motile, as determined by phase-contrast light microscopy. Examination by electron microscopy revealed wall-less cells delimited by a single membrane. The strain grew in M1D or R-2 liquid media at 20-40 6C, with optimum growth at 30 6C. Doubling time at the optimal temperature was 24 h. The strain catabolized glucose and hydrolysed arginine but did not hydrolyse urea. The DNA G+C content was 29.7±1 mol%. The genome size was~1.4-1.6 Mbp. Serological analysis, performed using the deformation test, did not reveal any reciprocal titres ¢320, indicating that strain TDA-040725-5 T had minimal cross-reactivity to strains of recognized species of the genus Spiroplasma. Based on this evidence, strain TDA-040725-5represents a novel species of the genus Spiroplasma, for which the name Spiroplasma eriocheiris sp. nov. is proposed, belonging to the novel Spiroplasma serological group XLIII.
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