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 μg/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.