Identification and combinatorial engineering of indole-3-acetic acid synthetic pathways in Paenibacillus polymyxa

Background Paenibacillus polymyxa is a typical plant growth-promoting rhizobacterium (PGPR), and synthesis of indole-3-acetic acid (IAA) is one of the reasons for its growth-promoting capacity. The synthetic pathways of IAA in P. polymyxa must be identified and modified. Results P. polymyxa SC2 and its spontaneous mutant SC2-M1 could promote plant growth by directly secreting IAA. Through metabonomic and genomic analysis, the genes patA, ilvB3, and fusE in the native IPyA pathway of IAA synthesis in strain SC2-M1 were predicted. A novel strong promoter P-04420 was rationally selected, synthetically analyzed, and then evaluated on its ability to express IAA synthetic genes. Co-expression of three genes, patA, ilvB3, and fusE, increased IAA yield by 60% in strain SC2-M1. Furthermore, the heterogeneous gene iaam of the IAM pathway and two heterogeneous IPyA pathways of IAA synthesis were selected to improve the IAA yield of strain SC2-M1. The genes ELJP6_14505, ipdC, and ELJP6_00725 of the entire IPyA pathway from Enterobacter ludwigii JP6 were expressed well by promoter P-04420 in strain SC2-M1 and increased IAA yield in the engineered strain SC2-M1 from 13 to 31 mu g/mL, which was an increase of 138%. Conclusions The results of our study help reveal and enhance the IAA synthesis pathways of P. polymyxa and its future application.

Automated summary

By identifying key genes involved in IAA synthesis in P. polymyxa SC2 and its mutant strain SC2-M1, and utilizing a novel strong promoter P-04420, the study successfully increased the IAA yield by 138% in the engineered strain SC2-M1. These results contribute to a better understanding and potential improvement of IAA synthesis pathways in P. polymyxa.