Mycelium-mediated transfer of water and nutrients stimulates bacterial activity in dry and oligotrophic environments

Anja Worrich,Hans-Hermann Richnow,Hryhoriy Stryhanyuk,Sara König,Thomas Banitz,Florian Centler,Lukas Y Wick,Matthias Kästner,Anja Miltner,Martin Thullner,Niculina Musat,Hauke Harms,Karin Frank

doi:10.1038/ncomms15472

Abstract

Fungal–bacterial interactions are highly diverse and contribute to many ecosystem processes. Their emergence under common environmental stress scenarios however, remains elusive. Here we use a synthetic microbial ecosystem based on the germination of Bacillus subtilis spores to examine whether fungal and fungal-like (oomycete) mycelia reduce bacterial water and nutrient stress in an otherwise dry and nutrient-poor microhabitat. We find that the presence of mycelia enables the germination and subsequent growth of bacterial spores near the hyphae. Using a combination of time of flight- and nanoscale secondary ion mass spectrometry (ToF- and nanoSIMS) coupled with stable isotope labelling, we link spore germination to hyphal transfer of water, carbon and nitrogen. Our study provides direct experimental evidence for the stimulation of bacterial activity by mycelial supply of scarce resources in dry and nutrient-free environments. We propose that mycelia may stimulate bacterial activity and thus contribute to sustaining ecosystem functioning in stressed habitats.

Highlights

Fungal–bacterial interactions are highly diverse and contribute to many ecosystem processes
We developed a synthetic microbial ecosystem to assess whether fungal–bacterial interactions emerge in presence of drought and nutrient limitation stress conditions
The mycelium-forming oomycete Pythium ultimum were inoculated to a water and nutrient-rich agar patch physically separated from the sporebearing silicon wafer (Fig. 1a)

Summary

Introduction

Fungal–bacterial interactions are highly diverse and contribute to many ecosystem processes. Fungi and bacteria co-inhabit a wide variety of environments[1,2] and their interactions are significant drivers of important ecosystem functions and services[3] In nature, they live in habitats exposed to fluctuating environmental conditions and frequently underlie strong selection pressure by limiting resources or drought[4]. We use a synthetic microbial ecosystem to examine whether mycelia of fungi and oomycetes reduce water and nutrient stress for bacteria and enable bacterial activity in otherwise dry and oligotrophic environments. Our results demonstrate that mycelium-forming fungi and oomycetes facilitate bacterial activity in dry and oligotrophic environments by providing nitrogen, carbon and water to bacteria and improving their habitat conditions

Methods

Results

Conclusion