A high-concentration-ammonium sulfate-requiring, ammonia-oxidizing bacterium, strain K1, was newly isolated from packed tower biological deodorization plants of chicken farms. The cells of strain K1 are rods (0.1-1.0 x 1.0-2.0 microm), gram negative, obligately aerobic, and nonmotile. Colonies (1-2 mm in diameter) on a plate culture are reddish, circular, and smooth. Intracytoplasmic membranes characteristic of nitrifying bacteria are present. The G+C content of the total DNA is 48.5 mol%. The similarity of 16S rRNA (%) to N. europaea ATCC 25978T (type strain) is 93.77%. This bacterium has a higher optimal growth temperature (35 degrees C) than is usually the case and tolerance up to 40 degrees C. The optimum concentration of ammonium sulfate in the medium is 303 mM, which should make it applicable for use in deodorization plants for enhancing the efficiency of deodorization. Phosphoglycerate kinase (PGK) and triosephosphate isomerase (TIM) were found to possess high specific activities (5700 and 4 x 10(5) U/mg, respectively) compared to the activities of these enzymes in strain ATCC 25978T (300 and 14 U/mg).