Hidden climatic risk posed by hydrocarbon bacteria

In a chip experiment conducted by Princeton researchers, soil mimics the interaction of soil, carbon compounds, and soil bacteria, creating new evidence that large molecules of carbon can potentially escape from the soil much faster than previously thought. In this microscope image, soil bacteria (red) grow around glucose (green) aggregates, which remain pores in the transparent synthetic clay. Loan: yudi Q. Young:

Much of the earth’s carbon is trapped in the ground, and scientists believe that potential climate warming compounds will remain safe there for centuries. But new research Princeton University shows that carbon molecules can potentially escape from the earth much faster than previously thought. The findings suggest a key role for some species of terrestrial bacteria that can produce enzymes that break down large carbon-based molecules and allow carbon dioxide to escape into the air.

Soil stores more carbon than all the plants on the planet, taken together in the atmosphere, and the soil absorbs about 20% of man-made carbon emissions. However, the factors influencing the accumulation of carbon և from soil emissions have been difficult to study, limiting the usefulness of soil carbon models in predicting climate change. New findings help explain growing evidence that large carbon molecules can be released from the soil faster than conventional models.

“We’ve come up with something out of the ordinary for biology, and its connection to the carbon footprint in the soil,” said Howard Stone, co-author of Donald R. Dixon ’69 և Elizabeth W. Dixon Professor of Mechanical Aerospace Engineering.

In a newspaper published today (January 27, 2021) Nature communications, researchers: former graduate fellow udi K. Led by Young, they developed experiments on “soil on a chip” to mimic the interactions of soils, carbon compounds, and soil bacteria. They used synthetic, transparent clay to care for the clay components of the soil, which play a major role in absorbing carbon-containing molecules.

Microfluidic device Look through the clay

The researchers coated the microfluidic device with clear clay, then added sugar molecules labeled as daylight, and under a microscope depicted the absorption and release of carbon from the clay. Loan: yudi Q. Young:

The “chip” was a modified slide of a microscope or microfluidic device containing waves half a centimeter long with silicone walls several times the width of a human hair (about 400 micrometers). Inlet and outlet pipes at each end of the channels allowed the researchers to inject a synthetic clay solution, followed by suspensions containing carbon molecules, bacteria, or enzymes.

After covering the holes with transparent clay, the researchers added sugar molecules labeled with daylight shocks to mimic the carbon-containing nutrients that leak from plant roots, especially during rain. The experiments allowed researchers to directly observe the locations of carbon compounds in clay and their movements in response to the flow of liquid in real time.

Both small and large sugar-based molecules adhered to the synthetic clay as they flowed through the device. In line with current models, small molecules were easily displaced, while larger ones remained in the clay.

When the researchers added Pseudomonas aeruginosa, a common soil bacterium, to the soil chip device, the bacteria could not reach the nutrients in the small holes in the clay. However, the enzyme dextranase, which is an enzyme released by certain soil bacteria, can break down nutrients contained in synthetic clay, making smaller sugar molecules available to nourish bacterial metabolism. In the environment, this can lead to the release of large amounts of CO2 from the soil into the atmosphere.

Researchers have often assumed that larger carbon compounds are protected from emissions when they adhere to clay surfaces, resulting in longer carbon storage. Some recent field studies have shown that these compounds can be separated from clay, but the reason for this has been mysterious, says lead author Ian, who conducted the study as a postdoctoral fellow at Princeton University and now an associate professor at the University of Minnesota.

“This is a very important phenomenon, because it suggests that carbon released into the soil can be emitted. [and play a role in] “Future climate change,” Ian said. “We are just bringing evidence of how this carbon can be emitted. We have found that enzymes produced by bacteria play a role, but this has often been overlooked in climate modeling studies, which suggest that clay has protected carbon in the soil for millennia.

The study is based on a talk by Stone ուր co-author Ian Burg, Assistant Professor of Civil and Environmental Engineering at the High Lawn Environmental Institute. Stone’s lab used microfluidic devices to study the properties of synthetic fibers and bacterial biofilms, while Pyramid has experience in surface geochemistry of minerals, which are thought to be the most effective in preserving carbonaceous matter from their soil carbon structure.

Stone, Burg և and their colleagues realized the need to experiment with some assumptions in widely used models of carbon storage. Yang joined Stone’s team to lead the research, and he partnered with Xinning Zhang, an assistant professor at the High Meadow Environmental Institute for Geological Sciences, to study bacterial metabolism and its interaction with the soil environment.

Inyun Tang, a researcher in the Department of Climate Science at Lawrence Berkeley National Laboratory, said that in recent years he and others have observed the breakdown of large carbon molecules in the soil, suggesting that it is mediated by biologically produced enzymes.

The Princeton team’s observations “strongly support our hypothesis,” said Tang, who did not participate in the study. He added that the study technique can also be used to study issues such as: “Will the reversible interaction of small carbon molecules, clay particles, lead to carbon starvation of bacteria, will it stabilize carbon?” And how do such interactions help maintain soil diversity? It’s a very interesting start. “

Future studies will test whether bacteria in the model system can release their own enzymes by breaking down large carbon molecules and using them for energy, releasing CO2 in the process.

Although it is possible to describe the stabilization of Tang carbon, the newly discovered phenomenon may also have the opposite effect, contributing to a positive response node that may deepen the rate of climate change, say the study authors. Other experiments have shown a “pre-emption” effect in which the addition of small molecules of sugar into the soil results in the release of carbon into the soil, which in turn can lead to faster bacterial growth. addition:

Reference. January 27, 2021 Nature communications,
DOI: 10.1038 / s41467-020-20798-6:

The study was supported by the Great Challenges program and the carbon offspring initiative of the Princeton High Meadows Environmental Institute.

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