Bacteria that eat methane and convert this greenhouse gas into fuel

A bacterium that eats methane and that could help capture this polluting gas from the atmosphere.

Bacteria that can convert methane from the air into usable products could be an essential tool for reducing greenhouse gas emissions, if we can understand how they do it.

New discovery could jump-start design efforts methane harvesting bacteriafight against greenhouse gas emissions and “exploit” the air in search of useful compounds.

Methane is a very potent greenhouse gas, 25 times more effective at trapping heat from the sun in the Earth’s atmosphere.

It is emitted by sources such as livestock, coal mines, oil pipelines or landfills, it accounts for 20% of all the greenhouse gases we emit, key to global warming.

In addition to reducing its emissions, one possible solution is to capture the methane we produce and convert it into other substances that can be reused. But it’s hard to control.

So-called “methanotrophic” bacteria consume about 30 million tonnes of atmospheric methane and transform it into less harmful compounds. And now it’s about trying to harness it for the good of all humanity.


How to convert atmospheric methane to methanol.

Atmospheric methane could provide us with a cheap and abundant source of fuel.

But economically today it is not profitable. To do this, researchers must optimize the chemical reactions that take place in bacteria to maximize the amount of methane that is converted.

It is necessary to know in detail the enzymes used by methanotrophs (pMMO). These large, complex proteins are known to bind methane to specific sites and are essential for catalyzing chemical reactions that convert methane.

The problem is that these enzymes are embedded in the delicate outer membranes of bacteria.

To study their structures at the atomic scale, researchers have until now had to resort to disruptive techniques to extract the enzymes from their hosts. When ripped from its natural environment in this way, pMMO’s activity stops completely, making it virtually impossible for researchers to understand how it interacts with methane.

New solution.

A team led by Amy Rosenzweig (Northwestern University) has taken an important step to overcome these issues.

His solution goes through a more careful procedure, in which the extracted enzymes are embedded into tiny nanodisks of lipids, the same fatty molecules that make up cell membranes. The idea is that the nanodisks resemble the native environment of the enzymes enough to continue reacting with methane.

Researchers could design artificial enzymes best suited to convert atmospheric methane into useful products.

Using a 3D imaging technique called ‘cryo-electron tomography’, they were able to study the behavior of enzymes up close, with a level of detail that allowed them to visualize the movements of individual atoms. The researchers found that when embedded in the nanodisks, the pMMO enzymes behaved completely differently from their counterparts that had been completely removed from cell membranes.

More importantly, by interacting with surrounding lipids, these enzymes retained their ability to interact with methane molecules. For the first time, this allowed the team to identify a previously undetected “binding site” on the enzymewhere the methane molecules probably undergo the reaction that converts them to methanol.

Precision bioengineering.

This discovery could have far-reaching implications for our ability to capture methane directly from the atmosphere. With a better understanding of the natural binding behavior of pMMO, researchers in future studies could design new artificial enzymes based on pMMO. When incorporated into the cell membranes of methanotrophs, these enzymes may be much better suited to converting atmospheric methane into useful products.

Researchers could dramatically increase the efficiency and yield of existing biofabrication processes, making them economically competitive. In turn, this could be a strong incentive for many industries to harness the methane they produce at its source, rather than letting it go to waste, warming the atmosphere.

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