Inter- and intracellular colonization of Arabidopsis roots by endophytic actinobacteria and the impact of plant hormones on their antimicrobial activity

Anne Van Der Meij,Martinus A Schneijderberg,Joost Willemse,Jos M Raaijmakers,René Geurts,Gilles P Van Wezel

doi:10.1007/s10482-018-1014-z

Abstract

Many actinobacteria live in close association with eukaryotes such as fungi, insects, animals and plants. Plant-associated actinobacteria display (endo)symbiotic, saprophytic or pathogenic life styles, and can make up a substantial part of the endophytic community. Here, we characterised endophytic actinobacteria isolated from root tissue of Arabidopsis thaliana (Arabidopsis) plants grown in soil from a natural ecosystem. Many of these actinobacteria belong to the family of Streptomycetaceae with Streptomyces olivochromogenes and Streptomyces clavifer as well represented species. When seeds of Arabidopsis were inoculated with spores of Streptomyces strain coa1, which shows high similarity to S. olivochromogenes, roots were colonised intercellularly and, unexpectedly, also intracellularly. Subsequent exposure of endophytic isolates to plant hormones typically found in root and shoot tissues of Arabidopsis led to altered antibiotic production against Escherichia coli and Bacillus subtilis. Taken together, our work reveals remarkable colonization patterns of endophytic streptomycetes with specific traits that may allow a competitive advantage inside root tissue.

Highlights

Actinobacteria represent a diverse phylum composed of both rod-shaped and filamentous bacteria that can be found in soil, marine and fresh water ecosystems (Goodfellow 2012)
A similar isolation approach was adopted for A. thaliana ecotype mossel (Msl) obtained from a natural ecosystem (Mossel, Veluwe, the Netherlands)
We show the recruitment of Streptomyces endophytes by A. thaliana Col-0 and A. thaliana Msl

Summary

Introduction

Actinobacteria represent a diverse phylum composed of both rod-shaped and filamentous bacteria that can be found in soil, marine and fresh water ecosystems (Goodfellow 2012). The concept of actinobacteria as free-living bacteria has more recently been challenged by studies pointing to their intimate relationships with diverse eukaryotes (Seipke et al 2012; van der Meij et al 2017). They have been found in association with vertebrates, invertebrates, fungi and plants. Actinobacteria are often welcome guests to their hosts due to their ability to produce chemically diverse natural products. Much of the chemical diversity of secondary metabolites produced by actinobacteria has likely evolved because of their interactions with other (micro)organisms in highly diverse environments (Seipke et al 2012; van der Meij et al 2017). Actinobacteria produce siderophores for iron acquisition as well as antibacterials and antifungals to protect their host against pathogens (Viaene et al 2016)

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Results

Conclusion