The lowest limit of pH for nitrification in tea soil and isolation of an acidophilic ammonia oxidizing bacterium

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Abstract
Investigation to determine the lowest limit of soil pH for nitrification were carried out in the laboratory using acid tea soils with pH range of 3.3 to 5.1. A significant linear correlation was observed between the soil pH value and nitrification rate which was measured by the soil incubation method. It was indicated that the lowest limit of the pH for nitrification was around pH 2.9. Two types of morphologically distinct strains of chemoautotrophic ammonia-oxidizing bacteria were isolated from four tested soils. One of them which was acidophilic was found to grow in a pH range from 3.5 to 7.0 in pure culture. The optimum pH for growth and ammonia oxidation of the acidophilic strain was pH 5.0. Acidophilic ammonia-oxidizing bacteria presumably play an important role in nitrification in acid tea soils.