Fig. 1
Biosynthesis of IAA inE. coliNissle 1917 strain. (A) Schematic representation of the heterologous IPyA pathway for IAA production from tryptophan (Trp) in the EcN strain. The IPyA pathway consists of three genes: aspC, ipdC, and iad1. The aspC gene encodes tryptophan aminotransferase, the ipdC gene encodes IPyA decarboxylase, and the iad1 gene encodes indoleacetaldehyde (IAAId) dehydrogenase. (B) Engineering of the IAA biosynthesis plasmids for enhanced production of IAA. The composition of the IPTG-inducible IAA biosynthesis plasmids (pTSN-IAA1, pTSN-IAA2, and pTSN-IAA3) is depicted. The EcN strains were transformed with plasmids pTSN-IAA1, pTSN-IAA2, and pTSN-IAA3 to create the EcN-IAA1, EcN-IAA2, and EcN-IAA3 strains, respectively. (C) Cell growth (OD600) of the engineered EcN strains (EcN-EV, EcN-IAA1, EcN-IAA2, and EcN-IAA3). EV represents the pTrc99A empty vector. (D) IAA titers (mg/L) of the engineered EcN strains. The engineered EcN strains were cultivated in IAA production medium with 2 g/L tryptophan and induced with different concentrations of IPTG at an OD600 of 0.6–0.8 for 24 h at 37 °C. After that, cell growth and IAA concentrations were measured using a UV-VIS spectrophotometer and HPLC analysis, respectively. Data represent the mean and standard deviation (SD) from three biological replicates