Nitrosospira, an important ammonium-oxidizing bacterium in fertilized coniferous forest soil

Abstract

Among ammonium-oxidizing autotrophic nitrifiers only Nitrosospira was found in 2 pine forest soils fertilized with urea or wood ash in southern Finland. A strain isolated from an ash-treated soil was partially characterized. The cells were spirals, mostly of 1-3 turns; they were flagellated or not and pili were found. The strain grew best at 20.degree.-27.degree. C at PO2 of 0.21 (shortest doubling time, 29 h). Km(O2) at 27.degree. C was 0.20 mg/l. Activity per cell during exponential growth ranged from 0.0060-0.0085 pmol NO2-/h and growth yield from 2.53 .times. 10 to 3.60 .times. 106 cells/.mu.mol NO2-. Pure cultures could not be isolated from urea-fertilized soils. Hyphomicrobium- and seliberia-like bacteria were frequent contaminants of enrichment cultures in these soils. Reasons for the persistence of Nitrosospira in forest soil were discussed.