Rapid and Sensitive Nitrosomonas europaea Biosensor Assay for Quantification of Bioavailable Ammonium Sensu Strictu in Soil

Abstract

Knowledge on bioavailable ammonium sensu strictu (i.e., immediately available for cellular uptake) in soil is required to understand nutrient uptake processes in microorganisms and thus of vital importance for plant production. We here present a novel ammonium biosensor approach based on the lithoautotrophic ammonia-oxidizing bacterium Nitrosomonas europaea transformed with a luxAB sensor plasmid. Bioluminescence-based ammonium detection was achieved within 10 min with a quantification limit in liquid samples of ∼20 μM and a linear response range up to 400 μM. Biosensor and conventional chemical quantification of ammonium in soil solutions agreed well across a range of sample and assay conditions. The biosensor was subsequently applied for a solid phase-contact assay allowing for direct interaction of biosensor cells with soil particle-associated (i.e., exchangeable plus fixed) ammonium. The assay successfully quantified bioavailable ammonium even in unfertilized soil and demonstrated markedly higher ratios of bioavailable ammonium to water- or 2 M KCl-exchangeable ammonium in anoxic soil than in corresponding oxic soil. Particle-associated ammonium contributed by at least 74% and 93% of the total bioavailable pool in oxic and anoxic soil, respectively. The N. europaea biosensor should have broad relevance for environmental monitoring of bioavailable ammonium and processes depending on ammonium bioavailability.

Nitrogen supply rate regulates microbial resource allocation for synthesis of nitrogen-acquiring enzymes

“…Organic N in the KCl extract (KCl-ON) was calculated as the difference between KCl-TN and KCl-IN. KCl-IN is readily available for utilization by soil microorganisms [ 15 ].…”

Molecular Biological Methods in Environmental Engineering

“…Dong et al (2011) developed a biosensor assay for the detection of bioavailable ammonium in soil using the bacterium Nitrosmonas europaea transformed with a luxAB sensor plasmid. The assay provided rapid results for both liquid and soil samples, with a quantification limit in liquid samples in the range of 20 μM to 400 μM.…”