The ‘Cyborg Soil’ Project Discovers a Complex Web of Hidden Microbial Cities
If you dig a teaspoon into the nearest clump of soil, you will find that it contains more microbes than there are people on the planet.
This is known via laboratory research that test samples of earth retrieved from the microbial wild to ascertain the types of tiny life that exist in the world beneath our feet.
The issue is that such research cannot tell us how this subterranean world of fungi, flagellates, and amoebae functions beneath the earth’s surface.
Due to the fact that these investigations involve the removal of soil from its natural environment, they obliterate the delicate structures of mud, water, and air in which soil bacteria live.
This motivated my lab to devise a method for spying on these underground workers, who are critical in their role as organic matter recyclers, without disturbing their microhabitats.
Our research uncovered the bacteria’ gloomy, damp cities. We discovered labyrinths of microscopic motorways, buildings, bridges, and rivers that bacteria traverse to obtain food or avoid being someone is next meal.
This unique window into what occurs beneath the Earth’s surface may help us better appreciate and maintain the planet’s increasingly degraded soils.
dirt made of cyborgs
In our research, we created a new type of “cyborg soil” that is half natural and half synthetic. It comprises of microengineered chips that we either buried in the wild or surrounding with soil in the laboratory for an extended period of time to allow for the emergence of microbial cities within the mud.
The chips serve as literal portals to the subterranean. The chip is carved to resemble the pore patterns of genuine soil, which are frequently bizarre and counter-intuitive at the scale at which bacteria experience them.
At the microscale, physical rules that are unfamiliar to us in the macro cosm become prevalent.
Water clings to surfaces, and the flow of water molecules pushes resting bacteria around. Due to the surface tension of the water surrounding them, air bubbles create insurmountable barriers for many bacteria.
After implanting our chips into the soil, we could observe bacteria passing through on their decomposition journeys, exposing their relationships, food webs, and the ways in which various microbes construct their surrounding, ever-changing microhabitats.
Highways of fungi
When we began excavating our first chips, we encountered a diverse array of single-celled organisms, nematodes, tiny arthropods, and bacteria species that live in our soils. Fungal hyphae, which burrow underground like plant roots, had soon colonized the depths of our cyborg soil pores, establishing a direct live link between the real soil and our chips.
This enabled us to investigate a phenomenon hitherto unknown outside of laboratory studies: the “fungal highways” along which bacteria “hitchhike” in order to disseminate through soil.
Bacteria often spread via water, so we could observe how bacteria smuggle themselves into new pores by following the grasping arms of fungal hyphae.
Surprisingly, we also discovered a high concentration of protists – mysterious single-celled organisms that are neither animal, plant, nor fungus – in the crevices between hyphae. Clearly, they, too, take a ride on the fungal highway — a phenomenon that has been fully unknown to yet.
We could also quantify how frequently this occurred because we studied several hundred different routes within our cyborg soil chips, containing many thousand individual pore spaces.
This demonstrates that hyphae must play a critical role in the spread of a diverse array of swimming microorganisms, providing them with a significant advantage while scavenging for food in subterranean microcities.
Engineering of the underground
Additionally, we intended to investigate how and by what ways microbial cities are constructed in our work.
One method we could do this was to observe how soil minerals migrated into our chips, forming pockets of natural soil space within the artificial buildings we would erected in the ground.
As our chips dried, we saw how water is pulled through soil pores: a tsunami of water movement that soil microorganisms are constantly exposed to as rain and shine tame their small homes.
The resulting patterns in the soil minerals resembled those found in our macro world’s riverbed system.
And it is not only physical forces that shape the soil bacteria’ environment. Fungi frequently operate as “ecosystem engineers” with their powerful hyphal tips, opening up passageways and blocking others with their cells. They are responsible for the majority of the microbial metropolis’s streets, avenues, and bridges.
Surprisingly, we discovered that other, less “strong” creatures had an effect on the microscopic structure of soils as well.
For example, a ciliate, which uses small hair-like extensions for mobility, may also bulldoze dirt through its voracious hunt for food.
Soil, science, and society are inextricably linked.
Our cyborg soil study contributes to the integration of field ecology and controlled laboratory studies. It combines the benefits of studying realistic, complex communities of soil organisms with the precision of carefully regulating and altering variables such as fertilizer delivery or temperature to observe how soils and their bacteria respond to changes above ground.
However, there is another advantage. We believe that by witnessing the hidden world of soils and their fascinating species, people can develop an emotional connection to this crucial ecosystem.
Other ecosystems have long featured charismatic animals that serve as ambassadors for conservation efforts.
On the other hand, soils continue to be associated with dirt and filthiness.
Nonetheless, soils underpin 95% of our food production. They store about twice as much carbon as the biosphere and atmosphere combined.
We want to demonstrate that as you dig your teaspoon into the dirt, you are actually excavating the upper reaches of an amazing secret metropolis that is home to a quarter of the Earth’s species. The adorable critters in your spoon are not filthy; they silently provide critical ecological functions that sustain all life above ground. These soil-city denizens require immediate protection.
Edith Hammer is an associate lecturer at Lund University’s Department of Biology.
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