Fungi awake bacteria from their slumber

June 7, 2017, Helmholtz Association of German Research Centres
The NanoSIMS is a secondary ion mass spectrometry system with a spatial resolution of down to 50 nanometres. This high resolution combined with its mass sensitivity make it possible to detect elements and isotopes on cell surfaces and chemical changes inside cells. This instrument is part of the newly established research platform, ProVIS. Dr. Niculina Musat and Dr. Hryhoriy Stryhanyuk (co-authors of the paper) during sample analysis. Credit: UFZ

When a soil dries out, this has a negative impact on the activity of soil bacteria. Using an innovative combination of state-of-the-art analysis and imaging techniques, researchers at UFZ have now discovered that fungi increase the activity of bacteria in dry and nutrient-poor habitats by supplying them with water and nutrients. The ability of fungi to regulate drought stress in soil and thus sustain ecosystem functions is an important insight in the context of climate change.

Many spread through the soil with a fine network of thin filaments known as hyphae. In their search for and nutrients the hyphae grow in different directions, constantly enlarging the network. Once found, water and nutrients are absorbed and transported through the hyphae, allowing them to be supplied to parts of the fungal network in dry or -poor areas of the soil. But it isn't only the fungus itself which benefits from the transport of material through the hyphal pipelines: bacteria, too, are kept supplied with the water and nutrients they need to thrive. This has now been demonstrated by a team of UFZ researchers in a study recently published in the journal Nature Communications. "We've suspected for a long time that fungi play an important role in the soil moisture budget," says UFZ environmental biotechnologist Prof. Matthias Kästner. "Now, using secondary ion mass spectrometry techniques (NanoSIMS and ToF-SIMS) from the ProVIS research platform at UFZ, we've finally obtained experimental evidence."

As part of their investigations, the researchers closely examined the transport of water, substrates and nutrients through the microscopically small hyphae of fungi. They grew the fungi on a of water, glucose and nitrogen-containing nutrients. The fungal hyphae had to pass through a dry, nutrient-free zone in order to grow through into a new area containing the culture medium. The inhospitable transition zone contained spores of the common soil bacterium Bacillus subtilis. Spores are inactive stages of Bacillus that form when there is insufficient water, food and nutrients available for bacterial growth. The bacteria go into a kind of dormant stage, from which they only awake once the are more favourable for living again.

These are fungal hypha and germinated cells of the bacterium Bacillus subtilis reveal the uptake of the stable isotope 15N (orange/red), with which the nitrogen-containing nutrients were labelled. The non-germinated spores (white rings) show no enrichment. This image was taken with the NanoSIMS, a secondary ion mass spectrometry system. Credit: UFZ

In the experiment, these conditions were indeed improved by the growth of the fungi: "As the fungal hyphae grew through the dry zone, the bacterial spores germinated and we noticed clear microbial activity," says UFZ environmental microbiologist Dr. Lukas Y. Wick. "The fungi obviously improved the environmental conditions for the bacteria and woke them from their slumber, like Sleeping Beauty." But what exactly happens at a chemical level when fungal hyphae grow in direct proximity to bacterial spores? To answer this question, the researchers 'labelled' the water, glucose and nitrogen-containing nutrients in the culture medium in advance with stable isotopes. If these substances were transferred from the fungus to the bacteria, they could be detected using the isotopic marker and the NanoSIMS method, with nano-scale spatial resolution. "The NanoSIMS method reveals the distribution of elements and isotops and therefore allows us to observe metabolic processes," Kästner explains. "As it turns out, we did find the stable isotopes of the labelled water, glucose and nitrogen-containing nutrients in the cell mass of the bacteria - which could only have come from the fungi."

This study has given the UFZ researchers another important insight into fungi and their important function in soils. Fungi serve as pumping stations and pipelines for water, substrates and nutrients and can colonise inhospitable locations, making them habitable for bacteria - and thus stimulate microbial activity in the soil. In previous work the researchers have already shown that fungal hyphae act as a kind of fungal highway for bacteria, allowing them to move around, and provide a hotspot for bacterial gene transfer. Wick continues: "The results of this latest study demonstrate once again that, through their interaction with bacteria, fungi play a significant, previously underestimated role in the soil ecosystem."

If a soil is contaminated with pollutants, for example, can break them down. But if the soil is too dry, the degradation processes will come to a standstill. "If the drought period lasts for a limited time, fungi have a stabilising effect and can keep soil processes going. This could be important specifically with regard to the impacts of climate change, if the ratio of dry to moist areas of soil dramatically increases," says Kästner. In future investigations, the researchers therefore intend to look even more closely at soil as a true ecosystem. "We want to carry out soil experiments under different environmental conditions and find out what influence fungal growth has on the breakdown of pollutants," says Wick. He adds: "It's important to have a better understanding of the role of fungi in the soil ecosystem. Only when we know how works can we respond to changes, for example those caused by , with informed decisions."

Bacteria on the 'Fungal Highway': Pseudomonas putida moving along hyphae of Cunninghamella elegans

Explore further: How fungi can improve the genetic makeup of bacteria

More information: Nature Communications (2017). DOI: 10.1038/NCOMMS15472

Related Stories

How fungi can improve the genetic makeup of bacteria

December 14, 2016

Soil bacteria use the extensively branched, thread-like structures of fungi to move around and access new food sources. In a new study published in the journal Scientific Reports, UFZ researchers have been able to demonstrate ...

Improving the biodiversity of green roofs

March 1, 2017

Using living organisms such as bacteria or fungi, as an alternative to chemical fertilisers, can improve the soil biodiversity of green roofs, according to new research from the University of Portsmouth.

Microbes rule in 'knee-high tropical rainforests'

January 12, 2017

Rainforests on infertile wet soils support more than half of all plant species. Shrublands on infertile dry soils in southwestern Australia, jokingly called "knee-high tropical rainforests", support another 20 percent of ...

Future climate models greatly affected by fungi and bacteria

August 28, 2015

Researchers from Lund University, Sweden, and USA have shown that our understanding of how organic material is decomposed by fungi and bacteria is fundamentally wrong. This means that climate models that include microorganisms ...

What you need to know about soil to keep your garden healthy

September 28, 2016

As the weather warms and days lengthen, your attention may be turning to that forgotten patch of your backyard. This week we've asked our experts to share the science behind gardening. So grab a trowel and your green thumbs, ...

Recommended for you

Computing the origin of life

December 14, 2018

As a principal investigator in the NASA Ames Exobiology Branch, Andrew Pohorille is searching for the origin of life on Earth, yet you won't find him out in the field collecting samples or in a laboratory conducting experiments ...

Black widow spiders dial up posture for survival and sex

December 14, 2018

A new study led by Western University's Natasha Mhatre shows that body dynamics and posture are crucial to how black widow spiders decode the important vibrations that travel through their webs and up their legs. Black widows ...

To repair DNA damage, plants need good contractors

December 13, 2018

When a building is damaged, a general contractor often oversees various subcontractors—framers, electricians, plumbers and drywall hangers—to ensure repairs are done in the correct order and on time.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.