Bacterial catabolism of indole-3-acetic acid

Indole-3-acetic acid (IAA) is a molecule with the chemical formula C10H9NO2, with a demonstrated presence in various environments and organisms, and with a biological function in several of these organisms, most notably in plants where it acts as a growth hormone. The existence of microorganisms with the ability to catabolize or assimilate IAA has long been recognized. To date, two sets of gene clusters underlying this property in bacteria have been identified and characterized: one (iac) is responsible for the aerobic degradation of IAA into catechol, and another (iaa) for the anaerobic conversion of IAA to 2-aminobenzoyl-CoA. Here, we summarize the literature on the products, reactions, and pathways that these gene clusters encode. We explore two hypotheses about the benefit thatiac/iaagene clusters confer upon their bacterial hosts: (1) exploitation of IAA as a source of carbon, nitrogen, and energy; and (2) interference with IAA-dependent processes and functions in other organisms, including plants. The evidence for both hypotheses will be reviewed foriac/iaa-carrying model strains ofPseudomonas putida,Enterobacter soli,Acinetobacter baumannii,Paraburkholderia phytofirmans,Caballeronia glathei,Aromatoleum evansii, andAromatoleum aromaticum, more specifically in the context of access to IAA in the environments from which these bacteria were originally isolated, which include not only plants, but also soils and sediment, as well as patients in hospital environments. We end the mini-review with an outlook foriac/iaa-inspired research that addresses current gaps in knowledge, biotechnological applications ofiac/iaa-encoded enzymology, and the use of IAA-destroying bacteria to treat pathologies related to IAA excess in plants and humans.