Indole-3-acetic acid biosynthetic pathway and aromatic amino acid aminotransferase activities in Pantoea dispersa strain GPK

Abstract

This investigation deals with the production of IAA by a bacterial isolate Pantoea dispersa strain GPK (PDG) identified by 16S rRNA gene sequence analysis. HPLC and Mass spectral analysis of metabolites from bacterial spent medium revealed that, IAA production by PDG is Trp-dependent and follows indole-3-pyruvic acid (IPyA) pathway. Substrate specificity study of aromatic amino acid aminotransferase (AAT) showed high activities, only when tryptophan (Trp) and ?-ketoglutarate (?-kg) were used as substrates. AAT is highly specific for Trp and ?-kg as amino group donor and acceptor, respectively. The effect of exogenous IAA on bacterial growth was established. Low concentration of exogenous IAA induced the growth, whereas high concentration decreased the growth of bacterium. PDG treatment significantly increased the root length, shoot length and dry mass of the chickpea and pigeon pea plants. Significance and Impact of the Study: This study demonstrates the Indole-3-acetic acid (IAA) producing and plant growth-promoting abilities of Pantoea dispersa. This study confirms the IAA biosynthetic pathway used by this bacterium. The work also signifies the role of exogenous IAA on bacterial growth, which may act as signalling molecule in rhizosphere. © 2013 The Society for Applied Microbiology.