Abstract
A flow biosensor for the detection of toxicity in water using the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea as a bioreceptor and a polymeric membrane ammonium-selective electrode as a transducer is described. The system is based on the inhibition effects of toxicants on the activity of AOB, which can be evaluated by measuring the ammonium consumption rates with the ammonium-selective membrane electrode. The AOB cells are immobilized on polyethersulfone membranes packed in a holder, while the membrane electrode is placed downstream in the flow cell. Two specific inhibitors of the ammonia oxidation—allylthiourea and thioacetamide—have been tested. The IC50 values defined as the concentration of an inhibitor causing a 50% reduction in the ammonia oxidation activity have been measured as 0.17 μM and 0.46 μM for allylthiourea and thioacetamide, respectively. The proposed sensor offers advantages of simplicity, speed and high sensitivity for measuring toxicity in water.
Highlights
The detection of toxicity in water caused by pollutants is of great importance for aquatic ecosystems and human health
Monitoring of oxygen consumption by microbial sensors composed of immobilized ammonia-oxidizing bacterium (AOB) cells and an oxygen electrode allows a rapid and accurate estimation of the inhibition effect on the ammonia oxidation [11,12]
When the bacteria were grown to the late logarithmic phase, the cells were collected by vacuum filtering with a polyethersulfone membrane
Summary
The detection of toxicity in water caused by pollutants is of great importance for aquatic ecosystems and human health. Ammonia-oxidizing bacteria (AOB) play an important role in the removal of ammonia for wastewater treatment [8]. They are considered to be extremely susceptible to a wide range of pollutants (i.e., inhibitors) including sulfur, aromatic, and halogenated compounds even at low concentrations [9]. Monitoring of oxygen consumption by microbial sensors composed of immobilized AOB cells and an oxygen electrode allows a rapid and accurate estimation of the inhibition effect on the ammonia oxidation [11,12]. We employ Nitrosomonas europaea (N. europaea) as an AOB model and an ammonium-selective membrane electrode as a transducer for measuring the inhibition effect of a toxicant on the AOB ammonia oxidation activity. The flow biosensing mode simplifies the sensor construction and permits one to execute the individual unit operations under optimum conditions rather than to operate them concurrently under compromised conditions [19]
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