Bacteria also make noises: a study shows that they can apparently produce a kind of percussion music. For this purpose, researchers have developed tiny drums with graphene membranes that can record the vibrations of individual bacteria and thus make them audible. According to them, the concept could benefit the testing of antimicrobial agents. Because drumming can be used to read precisely how a substance affects the microbes: the tests show, for example, that the lethal effect of an antibiotic can be recognized by the cessation of the beating of the head and flagella.
No matter how quietly we sneak, our movements generate vibrations and thus noise. Even very fine movements of living beings can still be recorded with modern instruments. For example, researchers have already recorded the crackling, crunching and cracking that worms and the like cause in the ground. However, there are still significantly smaller organisms that move and thus, at least theoretically, cause vibrations and thus noise. However, one might think that the tiny movements of microbes can no longer be recorded. But this is exactly what the researchers led by Farbod Alijani from the Technical University of Delft have now succeeded in doing.
The scientists originally studied the basic mechanics of graphene. “It is a form of carbon made up of a single layer of atoms and is also known as a miracle material. Because it is very strong, has good electrical and mechanical properties and is also extremely sensitive to external forces,” explains Alijani. At one point, as part of their research, Alijani and his colleagues wondered what would happen if this extremely delicate material came into contact with a single biological object – and a very tiny one at that. This is how the researchers finally developed their graphene-bacteria drums.
Percussion music of a special kind
The membranes of the “instruments” consist of ultra-thin graphene double layers. They cover circular cavities etched in silicon dioxide with a diameter of eight micrometers and a depth of 285 nanometers. Many of these drums are arranged next to each other on a silicon chip in order to be able to provide extensive test results. In order to record the movements of individual bacteria, one was attached to each of the graphene membranes. The whole system is in a nutrient solution. The researchers used the well-known intestinal bacterium Escherichia coli as a test microbe.
As the scientists report, they were actually able to detect a deflection of the graphene membranes due to the bacterial movements. These vibrations were detected using laser interferometry. A single Escherichia coli cell generates vibrations with amplitudes of up to 60 nanometers and exerts forces of up to six nanonewtons on the environment. These effects could also be represented as sounds, which enabled the researchers to make the microbes audible. “What we saw was amazing! When a single bacterium sticks to the surface of a graphene drum, it creates vibrations that we have been able to detect. It also enabled us to hear the sound of a single bacterium!” says co-author Cees Dekker from TU Delft.
As the scientists explain, the tiny vibrations are the result of the biological processes of the bacteria, to which the movements of their flagella contribute in particular. This was illustrated by experiments with E. coli strains that were genetically engineered to have different levels of locomotor activity depending on the number or activity of their flagella. “To understand how tiny these scourge strikes on graphene are, imagine that they are at least 10 billion times weaker than a boxer’s punch hitting a punching bag. Still, these nanoscale beats can be converted into audio tracks and listened to,” says Alijani.
Potential for antibiotics research
Further experiments by the researchers then illustrated the potential of the process for research. They administered antibiotic substances to “drummers” made from different strains of bacteria. It turned out that if the respective bacterium was resistant to the antibiotic, the oscillations simply continued at the same level as before. On the other hand, if it was susceptible to the drug, the vibrations would subside within an hour or two—until the beating eventually died out altogether with the death of the microbe. Thanks to the high sensitivity of the graphene drums, the effects of antibiotics can be precisely understood at the level of a single cell, the researchers emphasize.
“In the future, we want to further optimize our single-cell graphene antibiotic susceptibility platform and test it with different pathogens. Ultimately, the system could be used as an effective diagnostic tool for the rapid detection of antibiotic resistance in clinical practice,” hopes Alijani. His colleague Peter Steeneken concludes: “This would be an important tool in the fight against antimicrobial resistance, which is an increasing threat to human health around the world.”
Video © Irek Roslon – TU Delft
Source: Delft University of Technology, professional article: Nature Nanotechnology, doi: 10.1038/s41565-022-01111-6