Diversity and functions of volatile organic compounds produced by Streptomyces from a disease-suppressive soil

Viviane Cordovez,Hua Zhu,Jos M Raaijmakers,Victor J Carrion,Desalegn W Etalo,Roland Mumm,Gilles P Van Wezel

doi:10.3389/fmicb.2015.01081

Abstract

In disease-suppressive soils, plants are protected from infections by specific root pathogens due to the antagonistic activities of soil and rhizosphere microorganisms. For most disease-suppressive soils, however, the microorganisms and mechanisms involved in pathogen control are largely unknown. Our recent studies identified Actinobacteria as the most dynamic phylum in a soil suppressive to the fungal root pathogen Rhizoctonia solani. Here we isolated and characterized 300 isolates of rhizospheric Actinobacteria from the Rhizoctonia-suppressive soil. Streptomyces species were the most abundant, representing approximately 70% of the isolates. Streptomyces are renowned for the production of an exceptionally large number of secondary metabolites, including volatile organic compounds (VOCs). VOC profiling of 12 representative Streptomyces isolates by SPME-GC-MS allowed a more refined phylogenetic delineation of the Streptomyces isolates than the sequencing of 16S rRNA and the house-keeping genes atpD and recA only. VOCs of several Streptomyces isolates inhibited hyphal growth of R. solani and significantly enhanced plant shoot and root biomass. Coupling of Streptomyces VOC profiles with their effects on fungal growth, pointed to VOCs potentially involved in antifungal activity. Subsequent assays with five synthetic analogs of the identified VOCs showed that methyl 2-methylpentanoate, 1,3,5-trichloro-2-methoxy benzene and the VOCs mixture have antifungal activity. In conclusion, our results point to a potential role of VOC-producing Streptomyces in disease suppressive soils and show that VOC profiling of rhizospheric Streptomyces can be used as a complementary identification tool to construct strain-specific metabolic signatures.

Highlights

Disease-suppressive soils are soils in which plants are effectively protected from infections by specific root pathogens due to antagonistic activities of soil and rhizosphereorganisms (Hornby, 1983; Weller et al, 2002)
Diversity of Actinobacteria Isolated from Suppressive Soil Using PhyloChip-based metagenomic analyses, we previously described the diversity of the bacterial community associated with the rhizosphere of sugarbeet plants grown in a Rhizoctoniasuppressive soil (Mendes et al, 2011)
Most of the 381 volatile organic compounds (VOCs) detected for the different streptomycetes from the Rhizoctonia-suppressive soil were found to be specific for some isolates whereas fewer VOCs were found to be commonly produced by all isolates

Summary

Introduction

Disease-suppressive soils are soils in which plants are effectively protected from infections by specific root pathogens due to antagonistic activities of soil and rhizosphere (micro)organisms (Hornby, 1983; Weller et al, 2002). This phenomenon has been described worldwide, but the responsible (micro)organisms and underlying mechanisms are largely unknown for most. Streptomyces volatiles: diversity and functions suppressive-soils (Weller et al, 2002; Mendes et al, 2011; Chapelle et al, 2015). The natural functions of microbial VOCs and their modes of action remain largely unknown (Kai et al, 2009; Kim et al, 2012; Schmidt et al, 2015)

Methods

Results

Conclusion