Ureolytic nitrification at low pH by Nitrosospira spec.

An ureolytic ammonium-oxidizing chemolithotroph belonging to the genus Nitrosospira was shown to nitrify at pH 4.5 in a pH-stat with urea as a substrate. With ammonium as the sole substrate nitrification did not occur at pH values below 5.5. Nitrosomonas europaea ATCC 19718 and Nitrosospira briensis ATCC 25971 did not possess urease activity. The results indicate that in acid soils nitrification by ureolytic ammonium-oxidizing chemolithotrophs may not be restricted to microsites of neutral pH.