The disclosure relates to the production and the use, by genetic engineering, of plasmids and bacterial strains containing, on a short, precisely characterizable DNA segment, the gene tfdA or a gene almost identical to tfdA. The novel plasmids and microorganisms are suitable for the production of 2,4-D (2,4-dichlorophenoxyacetic acid)-monooxygenase, and as starting materials for the transfer, by genetic engineering of the 2,4-D-degrading property of this enzyme to various organisms.