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The soil beneath our feet, home to fungi, bacteria, beetles and worms, may not seem like the most jazzy environment. But if you stuck a powerful enough microphone in the soil, you’d be surprised at how hopping it is, acoustically speaking. That has led some microbiologists to wonder: Are there sounds that actually encourage microorganisms to grow? And could serenading a fungus make it twist and shout?
The answer, published in a study on Wednesday in the journal Biology Letters, is yes. Playing sound to Trichoderma harzianum, a green microscopic fungus that defends tree roots from pathogens, led to growth rates seven times as fast as those of fungus grown in the sound of silence. If the laboratory findings can be replicated in nature, then sound could be an unexpected new tool for improving the health of forests, encouraging beneficial microbes to take root and thrive.
In recent years, scientists have put microphones in environments of all kinds, including tropical trees and coral reefs. In the process, they have discovered that an environment’s sound can be linked to its biodiversity — often, the more complex the soundscape, the more diverse and healthy the inhabitants.
Research also shows that playing the sounds of intact ecosystems can help damaged ones recover. Off the coast of Adelaide, Australia, for instance, scientists found that the recorded sounds of healthy oyster reefs could lure new oyster larvae to areas destroyed by overfishing.
Sound also seems to help some bacteria grow, said Jake Robinson, a microbial ecologist at Flinders University in Australia who studies the soil microbiome. It was this work with bacteria that inspired Dr. Robinson and his colleagues to see if the same were true of a beneficial fungus.
First, the scientists lined big plastic tubs with soundproofing foam to make quiet places for their fungi to live in. Then they put petri dishes with a dab of T. harzianum in the tubs. Once a day, they played some of the dishes 30 minutes of white noise drawn from a YouTube video intended to help people with tinnitus.
Not exactly Mozart — but the team chose the video because it featured sounds that were similar to those used by others studying the effects of sound on bacteria. At the same time, they assessed how many spores the fungi were making and how much of the dish the cells covered.
“To begin with, it looked like not much was happening,” Dr. Robinson said. Dishes that were not exposed to white noise and those that were looked about the same.
Then, around Day 3 of the experiment, the fungi treated with sound went into overdrive. T. harzianum spores became bright green in color, and the white noise dishes were soon a mossy viridian. By Day 5, the researchers were able to calculate that exposing the fungi to sound had made them grow seven times as fast and produce more than four times as many spores.
It’s not clear why the sound had these effects. Dr. Robinson speculates that the sound waves may be striking receptors in the fungal cells that are sensitive to pressure. These receptors could then lead to a cascade of signals that switch on growth genes. The researchers plan to look closer at what genes are switched on and off in the presence of sound to help understand the effects.
Why would microbes evolve to grow better in the presence of sound? Perhaps silence indicates a hostile environment, one where no other organism has been able to grow. It might also be that certain kinds of sound fend some microbes off but give off a come-hither vibe to others. The researchers will be experimenting with other sounds and with communities of several microorganisms in future work, so they can better understand the connection between sounds and microbes’ response.
Looking ahead, Dr. Robinson wonders if sounds might someday be routinely used in woodland restoration projects, in which using the right makeup of soil microbes may be important to success.
“It might be you can create a certain soundscape that has an invigorating, growth-promoting effect,” he said — music to a forest’s ears.
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