Our goal was to investigate how root exudate flavonoids influence the soil bacterial community structure and to identify members of the community that change their relative abundance in response to flavonoid exudation. Using a model system that approximates flavonoid exudation of Medicago sativa roots, we treated a soil with 7,4′-dihydroxyflavone and naringenin in two separate experiments using three different rates: medium (equivalent to the exudation rate of 7,4′-dihydroxyflavone from M. sativa seedlings), high (10× the medium rate), and low (0.1× the medium rate). Controls received no flavonoid. Soil samples were subjected to ATP assays and 16S rRNA gene amplicon sequencing. The flavonoid treatments caused no significant change in the soil ATP content. With the high 7,4′-dihydroxyflavone treatment rate, operational taxonomic units (OTUs) classified as Acidobacteria subdivision 4 increased in relative abundance compared with the control samples, whereas OTUs classified as Gaiellales, Nocardioidaceae, and Thermomonosporaceae were more prevalent in the control. The naringenin treatments did not cause significant changes in the soil bacterial community structure. Our results suggest that the root exudate flavonoid 7,4′-dihydroxyflavone can interact with a diverse range of soil bacteria and may have other functions in the rhizosphere in addition to nod gene induction in legume—rhizobia symbiosis.

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Notes/Citation Information

Published in PLOS ONE, v. 11, no. 1, e0146555, p. 1-16.

© 2016 Szoboszlay et al.

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Funding Information

This work was supported by grant 2011-67020-30195 from the National Institute of Food and Agriculture of the United States Department of Agriculture to LAM.

Related Content

16S rRNA gene amplicon sequencing data are available at the National Center for Biotechnology Information Sequence Read Archive (www.ncbi.nlm.nih.gov/sra) under the accession number PRJNA295777.

journal.pone.0146555.s001.TIFF (23 kB)
S1 Fig. Standard curves of the ATP assays.

journal.pone.0146555.s002.XLSX (218 kB)
S1 Table. DESeq2 results comparing the control and high treatments from the 7,4′-dihydroxyflavone experiment.

journal.pone.0146555.s003.XLSX (214 kB)
S2 Table. DESeq2 results comparing the control and medium treatments from the 7,4′-dihydroxyflavone experiment.

journal.pone.0146555.s004.XLSX (213 kB)
S3 Table. DESeq2 results comparing the control and low treatments from the naringenin experiment.

journal.pone.0146555.s005.XLSX (214 kB)
S4 Table. DESeq2 results comparing the low and high treatments from the naringenin experiment.