Indole-3-acetic acid production from indole-3-acetonitrile in Bradyrhizobium

Abstract

Bradyrhizobium japonicum USDA 110, Bradyrhizobium elkanii USDA 76 and two Bradyrhizobium sp. strains, BTA-1 and BGA-1, produced indole-3-acetamide (IAM). IAM is a characteristic intermediate in indole-3-acetic acid production from tryptophan by the tryptophan-2-monooxygenase (TMO) pathway, by other bacteria, such as Agrobacterium tumefaciens and Pseudomonas savastanoi. However, none of these strains showed any TMO activity. Moreover, the TMO gene could not be detected when oligonucleotides from an Agrobacterium tumefaciens tms-1 gene conserved region were used to amplify a putative TMO gene in these strains, nor when a 600 bp heterologous probe from tms-1 was used for DNA/DNA hybridisation in a Bradyrhizobium genomic DNA library. Nitrile hydratase (Nhase) activity, producing IAM from indole-3-acetonitrile, was detected in all the four strains and we propose that Nhase activity is responsible for the presence of IAM in the Bradyrhizobium culture supernatants. This is the first time that a Nhase activity has been detected in Bradyrhizobium.