What are the Greenhouse Gases?

Have you ever been inside a car on a sunny day with the windows rolled up? At first, the car feels comfortably warm, but as time goes on, it becomes hotter and hotter. Sunlight enters through the windows and warms the inside of the car, but the heat gets trapped and cannot easily escape.

Something very similar happens on Earth. Our planet is surrounded by gases that act like the car windows, letting sunlight in while keeping some of the heat inside. These are the greenhouse gases, and they keep our planet warm by holding some of the Sun’s heat. Without them, our planet would be freezing, and it would be too cold for people, animals, and plants to survive. However, while greenhouse gases are fine in moderation, they are harmful in excess. When there are too many of them, they trap in too much heat and make Earth warmer than it should be. This process is known as the greenhouse effect, and it can have serious consequences for our planet. Even a couple of degrees increase from normal temperature can cause problems such as droughts, melting ice in the Arctic, rising sea levels, and longer heat waves. In other words, when the Earth gets warmer, climate change problems become worse [1].

The main greenhouse gases are carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). CO₂ is the most famous because it comes from burning things like coal, oil, and gas to make electricity, run cars, and power factories. If we can decrease the amount of CO₂ in the atmosphere, we could help restore a healthier temperature for the planet and create a safer and more comfortable environment for most living organisms. Earth has a natural solution: plants transform CO₂ into oxygen via photosynthesis. However, plants cannot remove enough CO₂ from the air because humans have reduced the amount of vegetation. Fortunately, scientists have found tiny organisms besides plants that can help reduce CO₂ levels and lighten the greenhouse effect [1, 2].

Unexpected Greenhouse Gas Fans: Homoacetogenic Bacteria

Bacteria are one of Earth’s oldest and most widespread forms of life, found nearly everywhere: in water, in soil, and even on our skin and inside our bodies. While some bacteria can cause illnesses, many are helpful. For example, certain bacteria in our intestines help digest food, while others can break down waste or even produce important medicines. On top of that, bacteria reproduce quickly, and some can survive in extreme environments, from icy glaciers to hot volcanoes.

Some bacteria are so unique that they can survive without oxygen! So, they do not breathe like humans or animals. Instead, to get energy, they replace oxygen with other environmental chemicals. Among the many types of bacteria that can live without oxygen, there is a special group called homoacetogenic bacteria. These tiny organisms turn out to be unexpected fans of greenhouse gases because they can use CO₂ and hydrogen (H₂) to grow and produce other chemicals. These invisible friends can even help scientists remove some of the greenhouse gases from the atmosphere (Figure 1).

Scientists are running experiments to learn more about how homoacetogenic bacteria work and find ways to make the process better. But first, they must answer an important question: Where do homoacetogenic bacteria live (Figure 2). Scientists must consider places where there is naturally very little or no oxygen, such as soil, lake bottoms, and wetlands, where these bacteria help break down dead plants and animals. Homoacetogenic bacteria are also found inside the stomachs of cows, goats, and other animals, where they help digestion. In wastewater treatment plants, they produce substances that help clean dirty water and even make energy. Some homoacetogenic bacteria can live in deep-sea hydrothermal vents, surviving in these super-hot and dark places by using gases from inside the Earth [3].

When scientists locate a possible source of homoacetogenic bacteria, they go on a bacteria treasure hunt. Usually, instead of searching lake bottoms or other places that are difficult to access, they look in simple locations like livestock poop and wastewater treatment plants. It might sound kind of gross, but it is super important! Once scientists collect their samples, they take them to the lab to test if the bacteria can survive on CO₂ alone. One of the most famous bacteria they have found is called Clostridium ljungdahlii, which was first discovered in a chicken yard and turned out to be the number one fan of CO₂.

Tiny Gas Removers, Mighty Fuel Creators

So, now you know that homoacetogenic bacteria are like tiny fighters that can eat CO₂ and help our planet. It sounds amazing, but it is not that easy. Just like we need multiple things to survive, these bacteria need more than CO₂. They also need a special energy source to power up, making H₂ a perfect match. Think of it like this: CO₂ is their meal, but H₂ is the fuel that helps them turn CO₂ into something useful.

An easy way to get a mix of CO₂ and H₂ gases is by using a waste gas called syngas. Syngas is made by heating plant residues without burning them, in a controlled industrial process. Syngas is produced separately, stored, and later used as a food source for our bacteria. When homoacetogenic bacteria are supplied with syngas, they transform CO₂ and H₂ into useful substances such as acetate and ethanol in a process called syngas fermentation (Figure 2). Acetate gives vinegar its sour taste, but it is also used to make fuel and other cool stuff in factories. Ethanol is a type of alcohol that helps power cars and other machines [2]. Fuels made from living things like plants or bacteria are called biofuels—so, these tiny gas fans are like nature’s little biofuel makers!

Turning Greenhouse Gases into a Better Future

Right now, homoacetogenic bacteria are still being studied and improved to achieve better results in syngas fermentation, while some companies have already created big industrial systems. For example, a large ethanol-producing industry feeds homoacetogenic bacteria with waste gases released by steel factories to produce fuel in the form of ethanol. The company also reuses industrial greenhouse gases, which avoids the release of CO₂ into the atmosphere [4].

In summary, homoacetogenic bacteria are tiny, powerful organisms that help reduce greenhouse gases like CO₂ by turning them into useful chemicals like acetate and ethanol. By doing so, they not only help the environment by removing CO₂, but also reduce dependence on fossil fuels by producing cleaner biofuels from acetate and ethanol. By learning more about homoacetogenic bacteria and their abilities, scientists hope to find ways to use them to fight climate change and create sustainable energy sources that are more environmentally friendly and will not run out.

Glossary

Greenhouse Gases: ↑ Gases in the atmosphere, like carbon dioxide (CO₂) and methane (CH₄). They keep our planet warm by holding some of the Sun’s heat, but excess, they cause climate change.

Atmosphere: ↑ The layer of gases that surround the Earth, keeping our planet warm and protected. Its composition is 78% nitrogen, 21% oxygen, and 1% of other gases, including CO₂.

Photosynthesis: ↑ A process in which plants make their food using CO₂ from the air, water from the ground, and energy from the sun.

Homoacetogenic Bacteria: ↑ Tiny organisms that live without oxygen. They use carbon dioxide and hydrogen to live and produce useful chemicals.

Syngas: ↑ A mixture of gases, mainly CO₂ and H₂. It is produced from plants or industrial waste and used to make fuels and chemicals.

Fermentation: ↑ A process in which tiny living things like bacteria or yeast break down food or gases to make energy and new substances.

Biofuels: ↑ Fuels made from living things like plants or bacteria. They can power cars, airplanes, or power plants. They are called “bio” because they come from things that can grow again.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

PN-V is thankful for the PhD fellowship provided by SECIHTI. JOO-S is thankful for the postgraduate fellowship provided by COPOCYT. This work was financially supported by “Fideicomiso 23871, administrado por el Consejo Potosino de Ciencia y Tecnología, en el marco de la Convocatoria 2023-01”.

AI Tool Statement

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