Applied and Environmental Science

Fungi Keep Bacteria Alive When Soils Dry Out

Fungi spread through the soil using a fine network of thin filaments known as hyphae.  When food and water are abundant at one location, the hyphae transport that abundance to other sections of the fungal network where they are needed, nourishing not only the fungus in question, but any soil bacteria that are present as well.

“We’ve suspected for a long time that fungi play an important role in the soil moisture budget,” said Prof. Matthias Kastner, part of the team at the Helmholtz Centre for Environmental Research (UFZ) in Leipzig, Germany, that explored the ability of fungi to regulate drought stress in soil and sustain ecosystems in the face of climate change.

The team grew the fungi in a culture medium of water, glucose, and nitrogen-containing nutrients, but they had to pass through a dry, nutrient-free zone to get to it.  The inhospitable transition zone contained spores of the common soil bacterium Bacillus subtilis.  Spores form when there are not enough water or nutrients available in soil for bacterial growth.  They keep the bacteria alive in a dormant stage from which they awaken when favorable living conditions return.

“As the fungal hyphae grew through the dry zone, the bacterial spores germinated and we noticed clear microbial activity,” said Dr. Lukas Y. Wick, another member of the UFZ team.  “The fungi obviously improved the environmental conditions for the bacteria and woke them from their slumber.”

To determine how the fungi performed this service, the team labeled the water, glucose, and nutrients in the medium with stable isotopes, then used ion mass spectrometry techniques (NanoSIMS and ToF-SIMS) from the ProVIS research platform at UFZ to find out if the fungi had transferred them to the bacteria.  They had.

The team had already seen that fungal hyphae served as a highway for soil bacteria, allowing them to move around and get together to transfer genes.  The benefits were not all one way, however.  If there are pollutants in the soil, bacteria can break them down.

“We want to carry out soil experiments under different environmental conditions,” said Wick.  “Only when we know how soil works can we respond to changes, for example those caused by climate change, with informed decisions.”

For more information, go to the June 7 issue of Nature Communications.