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Appl. Environ. Microbiol., Apr 1996, 1248-1251, Vol 62, No. 4
Copyright © 1996, American Society for Microbiology

A Microsensor for Nitrate Based on Immobilized Denitrifying Bacteria

LH Larsen, NP Revsbech and SJ Binnerup
Department of Microbial Ecology, Institute of Biological Sciences, University of Aarhus, DK-8000 Aarhus C, and Section for Microbiology, The Royal Veterinary and Agricultural University, DK-1958 Frederiksberg C, Denmark

A biosensor for NO(inf3)(sup-) was constructed by attaching a 30- to 70-(mu)m-wide capillary with immobilized denitrifying bacteria in front of an N(inf2)O microsensor. These bacteria reduced O(inf2) so that only bacteria in the very tip of the sensor were exposed to O(inf2) whereas bacteria at a greater depth could carry out the anaerobic process of denitrification. In the presence of acetylene, which inhibits nitrous oxide reductase, bacteria reduced NO(inf3)(sup-) (or NO(inf2)(sup-)) from the surrounding medium to N(inf2)O and the concentration sensed by the N(inf2)O microsensor was directly proportional to the concentration of NO(inf3)(sup-) in the medium. By applying a 250-(mu)m-long capillary in front of the N(inf2)O microsensor, the 90% response time of the biosensor was 50 s. Biosensors may also be made with nitrous oxide-deficient strains so that acetylene inhibition can be omitted.

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