Plant microbiome-dependent immune enhancing action of Echinacea purpurea is enhanced by soil organic matter content

Mona H Haron,David S Pasco,Colin R Jackson,Heather L Tyler,Nirmal D Pugh,Suman Chandra,Rita M Moraes

doi:10.1038/s41598-018-36907-x

Mona H Haron, David S Pasco + Show 5 more

Open Access

https://doi.org/10.1038/s41598-018-36907-x

Copy DOI

Abstract

We previously demonstrated that extracts from Echinacea purpurea material varied substantially in their ability to activate macrophages in vitro and that this variation was due to differences in their content of bacterial components. The purpose of the current study was to identify soil conditions (organic matter, nitrogen, and moisture content) that alter the macrophage activation potential of E. purpurea and determine whether these changes in activity correspond to shifts in the plant-associated microbiome. Increased levels of soil organic matter significantly enhanced macrophage activation exhibited by the root extracts of E. purpurea (p < 0.0001). A change in soil organic matter content from 5.6% to 67.4% led to a 4.2-fold increase in the macrophage activation potential of extracts from E. purpurea. Bacterial communities also differed significantly between root materials cultivated in soils with different levels of organic matter (p < 0.001). These results indicate that the level of soil organic matter is an agricultural factor that can alter the bacterial microbiome, and thereby the activity, of E. purpurea roots. Since ingestion of bacterial preparation (e.g., probiotics) is reported to impact human health, it is likely that the medicinal value of Echinacea is influenced by cultivation conditions that alter its associated bacterial community.

Highlights

Evidence from our lab[1,2,3,4] and others[5,6] supports the theory that the efficacy of E. purpurea against respiratory infections is dependent, at least in part, on its bacterial community
Root tissue from plants cultivated in soil containing a higher organic content (10.4–67.4%) had a higher bacterial load than roots grown in lower organic matter soil (2.5% and 5.6%), with higher organic matter treatments yielding bacterial loads of 2.4–4.1 × 107 cells per gram of root compared to 1.5–1.7 × 107 bacterial cells per gram in roots grown under low organic matter (Fig. 1B)
Comparison of roots grown in lower organic matter soil (2.5% and 5.6% treatments) to those cultivated in higher organic matter treatments (10.4%, 23.2%, and 67.4%), showed that the higher organic matter soils resulted in significantly higher bacterial loads (p = 0.005)

Summary

Introduction

Evidence from our lab[1,2,3,4] and others[5,6] supports the theory that the efficacy of E. purpurea against respiratory infections is dependent, at least in part, on its bacterial community (microbiome) Bacterial components of this microbiome can directly impact immune function[1,2,3,4,5] and plant-endophyte interactions can alter secondary metabolite production of the anti-inflammatory alkylamides[6]. An opposite effect has been observed with nitrogen fertilization - high rates of application reduce colonization of plants by bacterial endophytes[11,12] In light of these findings, the objective of the present study was to determine the contribution of soil organic matter, nitrogen fertilization, and moisture content on the immune enhancing activity of E. purpurea and evaluate shifts in the plant-associated bacterial community that could be responsible for the activity changes

Objectives

Methods

Results

Conclusion