Biosynthesis of indole-3-acetic acid in Azospirillum brasilense - Insightsfrom quantum chemistry

Quantum chemical methods AM1 and PM3 and chromatographic methods were used to qualitatively characterize pathways of bacterial production of indole-3- acetic acid (IAA). The standard free energy changes (Delta G degrees'(sum)) for the synthesis of tryptophan (Trp) from chorismic acid via anthranilic acid and indole were calculated, as were those for several possible pathway s for the synthesis of IAA from Trp, namely via indole-3-acetamide (IAN), i ndole-3-pyruvic acid (IPyA), and indole-3-acetonitrile (IAN). The Delta G d egrees'(sum) for Trp synthesis from chorismic acid was - 402 (- 434) kJ . m ol(-1) (values in parentheses were calculated by PM3). The Delta G degrees' (sum) for IAA synthesis from Trp were - 565 (- 54&) kJ . mol(-1) for the IA N pathway, -481 (- 506) kJ . mol(-1) for the IAM pathway, and - 289 (- 306) kJ . mol(-1) for the IPyA pathway. By HPLC analysis, the possibility was a ssessed that indole, anthranilic acid, and Trp might be utilized as precurs ors for IAA synthesis by Azospirillum brasilense strain SF 245. The results indicate that there is a high motive force for Trp synthesis from chorismi c acid and for IAA synthesis from Trp, and make it unlikely that anthranili c acid and indole act as the precursors to IAA in a Trp-independent pathway .