This invention relates to the isolation of nucleic acid fragments from Methylamons sp. that encode enzymes involved in denitrification. The enzymes arc useful in denitrification reactions and for the identification of other denitrifying bacteria. In addition, this invention also relates to the construction of chimeric genes encoding all or a substantial portion of the present genes in sense or antisense orientation, wherein the expression of the chimeric genes results in production of altered levels of the present gene products in the recombinant host.