Auxin Production Is a Common Feature of Most Pathovars of Pseudomonas syringae

We investigated indole-3-acetic acid (IAA) production by 57 pathovars of Pseudomonas syringae and related species. Most of those analyzed produced IAA, especially in the presence of tryptophan. Eight strains produced high IAA concentrations in the absence of Trp. The iaaM and iaaH genes of P. savastanoi pv. savastanoi were detected in a limited number of strains only, including the eight above-mentioned strains. Thus, IAA synthesis in most assayed strains of P. syringae and related species does not involve genes highly similar to iaaM and iaaH. In contrast, the iaaL gene encoding an IAA-lysine synthase was detected in most pathovars, and was often found on plasmids.