Bacterium-Based NO2− Biosensor for Environmental Applications

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American Society for Microbiology

RESUMO

A sensitive NO2− biosensor that is based on bacterial reduction of NO2− to N2O and subsequent detection of the N2O by a built-in electrochemical N2O sensor was developed. Four different denitrifying organisms lacking NO3− reductase activity were assessed for use in the biosensor. The relevant physiological aspects examined included denitrifying characteristics, growth rate, NO2− tolerance, and temperature and salinity effects on the growth rate. Two organisms were successfully used in the biosensor. The preferred organism was Stenotrophomonas nitritireducens, which is an organism with a denitrifying pathway deficient in both NO3− and N2O reductases. Alternatively Alcaligenes faecalis could be used when acetylene was added to inhibit its N2O reductase. The macroscale biosensors constructed exhibited a linear NO2− response at concentrations up to 1 to 2 mM. The detection limit was around 1 μM NO2−, and the 90% response time was 0.5 to 3 min. The sensor signal was specific for NO2−, and interference was observed only with NH2OH, NO, N2O, and H2S. The sensor signal was affected by changes in temperature and salinity, and calibration had to be performed in a system with a temperature and an ionic strength comparable to those of the medium analyzed. A broad range of water bodies could be analyzed with the biosensor, including freshwater systems, marine systems, and oxic-anoxic wastewaters. The NO2− biosensor was successfully used for long-term online monitoring in wastewater. Microscale versions of the NO2− biosensor were constructed and used to measure NO2− profiles in marine sediment.

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