Identification of indole-3-acetic acid producing freshwater wetland rhizosphere bacteria associated with Juncus effusus L.

Production of indole-3-acetic acid (IAA), a key physiological feature of culturable, O2-tolerant bacteria associated with the freshwater macrophyte Juncus effusus L., was examined over a period of 2 years. Up to 74% of rhizobacteria identified and tested produced IAA. The number of indoleacetic acid producers decreased in winter. IAA was produced even when L-tryptophan, a precursor of IAA, was not added to the medium. Most of the IAA-producing strains were dominated by strains that were not identifiable to species level on the basis of API testing. Based on 16S rRNA gene sequencing and fatty acid analysis, it was found that IAA-producing rhizosphere bacteria associated with the freshwater wetland plant Juncus effusus L. are representatives of several families, including the Enterobacteriaceae, Pseudomonadaceae, Aeromonadaceae, Burkholderiaceae, and Bacillaceae. This study identifies numerous potentially important bacterial physiological groups of freshwater wetlands. Additionally, the study provides a baseline for monitoring and assessing the mutualistic relationships of wetland plants with rhizosphere bacteria in freshwater wetlands.