Possible use of N₂O in MPN tubes for enumeration of denitrifiers

N₂O when used in most probable number tubes as the only electron acceptor was not consumed at dilutions, down to 10⁻³ per gram. Additions of fresh carbon source and NO₃ after growth did not stimulate N₂O reduction. Since pure cultures of denitrifiers grew well under the same conditions this result was unexpected, the explanation has not been found. This approach, if successful, has the advantage that only denitrifiers can reduce N₂O to N₂. Further work in designing a method to use N₂O as an electron acceptor in MPN tubes is suggested.