A fragrant neighborhood: volatile mediated bacterial interactions in soil.

Kristin Schulz-Bohm,Paolina Garbeva,Wietse De Boer,Hans Zweers

doi:10.3389/fmicb.2015.01212

Abstract

There is increasing evidence that volatile organic compounds (VOCs) play essential roles in communication and competition between soil microorganisms. Here we assessed volatile-mediated interactions of a synthetic microbial community in a model system that mimics the natural conditions in the heterogeneous soil environment along the rhizosphere. Phylogenetic different soil bacterial isolates (Burkholderia sp., Dyella sp., Janthinobacterium sp., Pseudomonas sp., and Paenibacillus sp.) were inoculated as mixtures or monoculture in organic-poor, sandy soil containing artificial root exudates (ARE) and the volatile profile and growth were analyzed. Additionally, a two-compartment system was used to test if volatiles produced by inter-specific interactions in the rhizosphere can stimulate the activity of starving bacteria in the surrounding, nutrient-depleted soil. The obtained results revealed that both microbial interactions and shifts in microbial community composition had a strong effect on the volatile emission. Interestingly, the presence of a slow-growing, low abundant Paenibacillus strain significantly affected the volatile production by the other abundant members of the bacterial community as well as the growth of the interacting strains. Furthermore, volatiles released by mixtures of root-exudates consuming bacteria stimulated the activity and growth of starved bacteria. Besides growth stimulation, also an inhibition in growth was observed for starving bacteria exposed to microbial volatiles. The current work suggests that volatiles produced during microbial interactions in the rhizosphere have a significant long distance effect on microorganisms in the surrounding, nutrient-depleted soil.

Highlights

Microorganisms produce a great variety of secondary metabolites including antibiotics, toxins, pigments, and others
Our results demonstrated that both microbial interactions and shifts in microbial community composition had a significant effect on the volatile emission and that the presence of slow growing, non-abundant bacterial species influenced the volatile production of the bacterial community
For bacteria incubated in rhizospheric soil microcosms, it was observed that the volatiles produced by the mixture differed from those produced by each strain

Summary

Introduction

Microorganisms produce a great variety of secondary metabolites including antibiotics, toxins, pigments, and others. Research of the last decades demonstrated that bacteria produce a large set of VOCs (Kai et al, 2009; Insam and Seewald, 2010; Effmert et al, 2012; Bitas et al, 2013; Peñuelas et al, 2014). Similar to well-studied plant VOCs, it can be assumed that VOCs released by bacteria perform diverse and crucial functions (Bitas et al, 2013). Culture conditions including nutrient availability (Kai et al, 2009; Insam and Seewald, 2010) and the type of incubation medium substantially affect the spectrum of released VOCs (Weise et al, 2012). Bacteria produce a different set of volatiles when incubated in soil as compared to incubations on agar plates (Garbeva et al, 2014b)

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Conclusion