Comparative evaluation of naphthalene 1,2-dioxygenase effect on the productivity of indole-3-acetic acid synthesis and the growth-stimulating activity of Pseudomonas spp.

Rhizobacteria synthesizing indole-3-acetic acid (IAA) are often used to stimulate plant growth. To enhance IAA production by the rhizospheric bacterium Pseudomonas baetica MGMM504 during the growth on a tryptophan medium, a plasmid encoding naphthalene 1,2-dioxygenase synthesis genes (EC 1.14.12.12) was introduced. The expression of naphthalene 1,2-dioxygenase genes increased IAA synthesis in P. baetica MGMM504(pJeM2:nahA) by 40 % compared with the control. At the same time, P. putida PCL1760(pJeM2:nahA) showed no significant increase in IAA synthesis compared with PCL1760(pJeM2), which produced only trace amounts of IAA. The tests on wheat revealed a higher plant growth stimulating activity of P. baetica MGMM504(pJeM2:nahA), increasing the root length and germination of wheat seedlings by 45 % and 15 %, respectively, compared with P. baetica MGMM504(pJeM2). Neither variant of P. putida PCL1760 exhibited a phytostimulatory effect. The findings suggest that naphthalene 1,2-dioxygenase promotes the formation of an intermediate, which in itself is not a phytostimulator, but can be converted into one if a specialized IAA synthesis system is present in the strain.