[2] Pseudomonas and Burkholderia species produce pyrrolnitrin from tryptophan as secondary metabolite.

[6][7] In Pseudomonas fluorescens, biosynthesis of pyrrolnitrin requires four genes, named prnABCD, arranged into a single operon.

The products of these genes are similar in size and catalyze four subsequent reactions:[1][5] Except for prnA, these enzymes are unable to act on D-tryptophan.

[1] An alternative pathway was also suggested, where L-tryptophan is first turned into aminophenylpyrrole (APP) and then by subsequent steps to aminopyrrolnitrin and pyrrolnitrin.

While these steps have not been described in more detail, prnB is able to produce APP, presumably from tryptophan as starting material.