Methane, Methanotrophs, and The Microbial Roots of Climate Change

Methane (CH₄) may not be as talked-about as other greenhouse gases like carbon dioxide, but the “super pollutant” is a major contributor to climate change.

Heat-trapping methane is emitted from human industries like agriculture, oil and gas, and waste management. But it also occurs naturally in the environment. As certain microscopic organisms break down organic (living) matter into simpler parts, they release methane as a byproduct. At the same time, other microbes consume methane as an energy source.

As anthropogenic (human-caused) methane emissions rise, researchers are now treating methane-eating bacteria as potential climate solutions. Let’s investigate how methane functions, where it comes from, and how microscopic organisms might be the key to tackling it. 

Methane Emissions 101

Methane concentrations in the atmosphere have more than doubled in the last 200 years, leading the IPCC to declare that tackling methane emissions will be critical for limiting the worst impacts of climate change.^1,2 Pound for pound, the gas’ global warming potential is 86 times greater than CO₂ over a 20-year period and 34 times greater over 100 years.³

While methane is extremely powerful from a heat-trapping perspective, it’s short-lived. It persists in the environment for 10-12 years compared to carbon dioxide’s thousands.^4,5 Therein lies an opportunity: If we’re able to reduce methane emissions, positive climate impacts could follow relatively quickly.

Roughly 60% of these emissions are the result of human activity—primarily in the agriculture, waste, and fossil fuel sectors. (The other 40% comes from natural sources like wetlands, seabeds, and volcanoes.)^6,7 

On the farm, ruminant animals like cattle, pigs, sheep, and goats emit methane during digestion. As the bacteria in their gut breaks down food, methane is created, which the animals then release via burps and farts. While other animals (like termites) also create methane as a byproduct of digestion, livestock have an outsized impact on overall methane emissions.⁸ A single cow can emit 150–500 grams of the gas per day, similar to driving a gas-powered car up to 35 miles.⁹

Methane can also form when animal manure is left to decompose in lagoons or holding tanks, and when crops are intentionally flooded to control weeds and pests (common in rice production). 

Off the farm, methane is released as trash breaks down in landfills, during wastewater treatment, and at various points of the oil and gas production process.

Methanogens vs. Methanotrophs: A Bacterial Back-And-Forth

Microbes are the unseen orchestrators of the methane cycle. They can both create CH₄ under certain conditions and consume it under others. Let’s zoom in on the two groups of microorganisms that form the biological push and pull of methane in our environment: methanogens and methanotrophs. 

• Methanogens are microbes from the domain Archaea that produce methane as a byproduct of breaking down carbon-based compounds in anaerobic environments.¹⁰ (Think: The stomach of a cow or the depths of a landfill.) They are the only known organisms capable of producing methane, but they require a totally oxygen-free environment to do it.
• Methanotrophs, on the other hand, are microorganisms (mostly bacteria) that consume methane as an energy source.¹¹ They essentially “eat” methane before it escapes into the atmosphere, breaking it down into water and less potent carbon dioxide. (It’s worth noting that this process still releases greenhouse gas into the environment, demonstrating how important it is to reduce methane emissions in the first place.) Unlike methanogens, methanotrophs can survive in oxygenated environments. These methane-hungry bacteria may prove helpful for converting methane into useful products like biofuels (more on this below).

The interplay between methanogens and methanotrophs helps dictate whether a given environment is a methane source (releasing methane into the atmosphere) or sink (absorbing methane from the atmosphere). 

Fighting Methane Emissions With Microbes

Microbial balance clearly plays a powerful—and underappreciated—role in regulating the methane levels around us. Here are a few ways that researchers are starting to leverage microscopic bacteria to mitigate the super pollutant:

• Recently, there’s been a lot of rumbling (no pun intended) about how adjusting ruminants’ diets might change their stomach conditions and reduce the amount of methane-packed gas they send into the atmosphere. Just as certain foods and probiotics can help reduce gas in humans, they may do the same for livestock.¹² However, cattle nutrition is just one part of the equation. In order to significantly cut emissions from agriculture, we’ll need to switch to more soil bacteria-friendly farming practices, reduce global meat consumption, and waste less food.¹³ 
• Rice paddies tend to be a significant source of methane emissions. Since they’re often flooded to control pests and weeds, they can become anaerobic environments that are conducive to methanogenic (methane-emitting) archaea. Other methods for growing rice, like alternating periods of wetting and drying, may help reduce methane emissions and water use at the same time.¹⁴
• Adjusting landfill design may help breed more methane-eating bacteria. Early research suggests that adding substances like sulfate and iron to landfill mounds can promote methane removal (even in oxygen-free conditions).¹⁵ This isn’t a get-out-of-climate-jail free card: To cut emissions, we’ll also need to dramatically reduce the amount of waste we send to landfills in the first place.
• Certain “extreme” landscapes—such as geothermal springs and volcanic soils—are teeming with methane-gobbling methanotrophs. Some researchers are now studying how the microbes in these areas have naturally evolved to capture methane, in case any of their adaptations provide opportunities for innovation.
• Methanotrophs have also caught the attention of the biomanufacturing industry. Researchers are now testing how certain strains can convert captured methane into products like bioplastics, reducing the demand for fossil fuels.¹⁶ 

The Key Insight

Microbes are central to the methane cycle, capable of both producing and consuming the potent greenhouse gas. These methanogens and methanotrophs remind us that some of nature’s tiniest residents could be capable of tackling its largest problems.