Nitrite-oxidizing activity responds to nitrite accumulation in soil

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The factors influencing how soil nitrite (NO2−)- and ammonia (NH3)-oxidizing activities remain coupled are unknown. A short-term study (<48 h) was conducted to examine the dynamics of NO2−-oxidizing activity and the accumulation of NO2− in three Oregon soils stimulated by the addition of 1 mM NH4+ in soil slurry. Nitrite initially accumulated in all three soils; its subsequent decline or slowing of the accumulation of the NO2− pool by 24 h was accompanied by an increase in the size of the nitrate (NO3−) pool, indicating a change in NO2− oxidation kinetics. Bacterial protein synthesis inhibitors prevented the NO2− pool decline, resulting in a larger accumulation in all three soils. Although no significant increases in NO2−-oxidizing bacteria nxrA (Nitrobacter) and nxrB (Nitrospira) gene abundances were detected over the time course, maximum NO2− consumption rates increased 2-fold in the treatment without antibiotics compared to no change with antibiotics. No changes were observed in the apparent half saturation constant (Km) values for NO2− consumption. This study demonstrates phenotypic flexibility among soil NO2− oxidizers, which can undergo protein synthesis-dependent increases in NO2− consumption rates to match NH3 oxidation rates and recouple nitrification.

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