Nitrite-oxidizing activity responds to nitrite accumulation in soil

Abstract

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 two-fold in the treatment without antibiotics compared to no change with antibiotics. No changes were observed in the apparent half-saturation constant (K_m) 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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