Edith Hammer, lecturer (Biology) at Lund University (Sweden) has written a July 22, 2021 essay for The Conversation (h/t July 23, 2021 news item on phys.org) that has everything.: mystery, cyborgs, unexpected denizens, and a phenomenon explored for the first time (Note: Links have been removed),
Dig a teaspoon into your nearest clump of soil, and what you’ll emerge with will contain more microorganisms than there are people on Earth. We know this from lab studies that analyse samples of earth scooped from the microbial wild to determine which forms of microscopic life exist in the world beneath our feet.
The problem is, such studies can’t actually tell us how this subterranean kingdom of fungi, flagellates and amoebae operates in the ground. Because they entail the removal of soil from its environment, these studies destroy the delicate structures of mud, water and air in which the soil microbes reside.
This prompted my lab to develop a way to spy on these underground workers, who are indispensable in their role as organic matter recycling agents, without disturbing their micro-habitats.
Our study revealed the dark, dank cities in which soil microbes reside [emphasis mine]. We found labyrinths of tiny highways, skyscrapers, bridges and rivers which are navigated by microorganisms to find food, or to avoid becoming someone’s next meal. This new window into what’s happening underground could help us better appreciate and preserve Earth’s increasingly damaged soils.
Here’s how the soil scientists probed the secrets buried in soil (Note: A link has been removed),
In our study, we developed a new kind of “cyborg soil”, which is half natural and half artificial. It consists of microengineered chips that we either buried in the wild, or surrounded with soil in the lab for enough time for the microbial cities to emerge within the mud.
The chips literally act like windows to the underground. A transparent patch in the otherwise opaque soil, the chip is cut to mimic the pore structures of actual soil, which are often strange and counter-intuitive at the scale that microbes experience them.
Different physical laws become dominant at the micro scale compared to what we’re acquainted to in our macro world. Water clings to surfaces, and resting bacteria get pushed around by the movement of water molecules. Air bubbles form insurmountable barriers for many microorganisms, due to the surface tension of the water around them.
Here’s some of the what they found,
When we excavated our first chips, we were met with the full variety of single-celled organisms, nematodes, tiny arthropods and species of bacteria that exist in our soils. Fungal hyphae, which burrow like plant roots underground, had quickly grown into the depths of our cyborg soil pores, creating a direct living connection between the real soil and our chips.
This meant we could study a phenomenon known only from lab studies: the “fungal highways” along which bacteria “hitchhike” to disperse through soil. Bacteria usually disperse through water, so by making some of our chips air-filled we could watch how bacteria smuggle themselves into new pores by following the groping arms of fungal hyphae.
Unexpectedly, we also found a high number of protists – enigmatic single-celled organisms which are neither animal, plant or fungus – in the spaces around hyphae. Clearly they too hitch a ride on the fungal highway – a so-far completely unexplored phenomenon.
The essay has a number of embedded videos and images illustrating a fascinating world in a ‘teaspoon of soil’.
Here’s a link to and a citation for the study by the researchers at Lund University,
Microfluidic chips provide visual access to in situ soil ecology by Paola Micaela Mafla-Endara, Carlos Arellano-Caicedo, Kristin Aleklett, Milda Pucetaite, Pelle Ohlsson & Edith C. Hammer. Communications Biology volume 4, Article number: 889 (2021) DOI: https://doi.org/10.1038/s42003-021-02379-5 Published: 20 July 2021
This paper is open access.