Characteristics of an ammonia-oxidizing bacterium with a plasmid isolated from alkaline soils and its phylogenetic relationship

An ammonia-oxidizing bacterium, strain TCH716, was isolated from alkaline s oil at Harbin city, China. The cells of strain TCH716 are lobate (0.8-1.5 x 1.0-2.0 mum), gram-negative, obligately aerobic, and nonmotile. Colonies ( 1-2 mm in diameter) on gellan gum plate culture are reddish, circular, and smooth. The G+C content of DNA is 54.78 mol%. Its percentage of 16S rRNA ge ne sequence similarity (%) to Nitrosolobus multiformis ATCC 25196(T) (type strain) is 98.56%. This bacterium has an optimal growth temperature and pII at 30 degreesC and 8.0-8.5, respectively. The concentration of ammonium su lfate in the HEPES medium for optimum growth of this bacterium is 38 mM. St rain TCH716 was found to have a plasmid (approximately 6.5 kbp) that posses sed a plasmid-linked gene for sulfonamide resistance. Phosphoglycerate kina se, RubisCO and PEPC were found to possess high specific activities compare d to the activities of these enzymes in strain ATCC 25978(T) In identificat ion of strain TCH716, both morphological characteristics (compartmentalized cells) and the phylogenetic relationship based on 16S rRNA gene sequence a re important. Based on results obtained, strain TCH716 belongs to the genus Nitrosolobus, and designated as Nitrosolobus sp. TCH716.