Dr. Lisa Stein, professor at the University of Alberta and Canada Research Chair for Climate Change Microbiology
Dr. Lisa Stein, professor at the University of Alberta and Canada Research Chair for Climate Change Microbiology

A Tale of Two Gases: Mitigation and removal of methane and nitrous oxide emissions

06/19/24   |   Written by Homeworld Collective

An interview with Lisa Stein, PhD

Professor Lisa Stein is a world leader in methane and nitrogen microbiology. She’s currently a professor at the University of Alberta, where she is also a Canada Research Chair for Climate Change Microbiology. Before that, she was an assistant professor at UC Riverside, a postdoc at Caltech and a PhD student at Oregon State University.

Professor Stein studies the physiology of nitrifiers — interesting, important, and difficult-to-work-with microbes that can make nitrous oxide. Throughout her work, she’s demonstrated how interlinked nitrous and methane microbiology are.

Recently, Professor Stein and methylotroph expert Professor Mary Lidstrom published a perspective article in Science with critical insight on this topic. As more groups work on methane (including Spark Climate Solutions and Global Methane Hub) it’s imperative that strategies to mitigate greenhouse gas (GHG) emissions consider methane and nitrous oxide together, not as separate entities. 

Professor Stein is also a longtime friend of Homeworld and one of the very first guests on The Climate Biotech Podcast! Our Executive Director Dan Goodwin and Science Director Paul Reginato sat down with her to talk about microbes, methane, GHG mitigation, and so much more.

Listen to the full conversation on Spotify or Apple Podcasts, or read on for snippets from the episode (lightly edited for clarity).

Lisa Stein, a woman with short blonde hair, holds a glass bottle in a scientific laboratory.
Dr. Lisa Stein, professor at the University of Alberta and Canada Research Chair for Climate Change Microbiology

Why did you decide to work on the climate change microbiology?

“I am from Colorado and grew up in Gunnison, which is in the middle of the Rocky Mountains. I have a large appreciation for wilderness, lakes, water, clean air, and I think that’s largely why I’m still looking at environmental science for my career.

My degree is in traditional molecular biology. Because I had this really strong desire to do environmental science, I tried to find something that would be molecular biology related, but applied to the environment. When I applied for graduate school, I met a researcher involved in bioremediation. That was how I started with microbes.

It was 1981 when the first major paper came out that showed nitrifiers can be major sources of nitrous oxide to the atmosphere. This was way before ‘climate change’ was a word in the regular language of the world. I was really interested in that, and I’m still studying the physiology of how these microbes can make nitrous oxide.

And then with the methane cycle — that came later because [nitrifiers and methane oxidizers] are really closely related evolutionarily. They have a lot of metabolism in common. But that’s why I started studying methane … It came out of my love for studying nitrifiers.”

Why does methane matter for short-term climate mitigation?

“Nitrous oxide and carbon dioxide can stay in the atmosphere for a century or more, so our opportunity to slow temperature increase really hinges on our ability to control methane emissions.

Because [methane] has a higher heating capacity and a shorter residence time, removing it now can actually make a difference to the rate of temperature increase. Whereas if we remove all the CO2 we want right now in our lifetimes, we will not see a difference in temperature increase because of the amount of time that those gasses remain [in the atmosphere].”

We followed up with Professor Stein to clarify why the short residence time of methane means removing it now is important: There is a positive feedback between methane concentration in the atmosphere and its residence time. Since methane decays by reacting with and depleting atmospheric oxidants, avoiding or removing methane emissions can additionally lower the residence time of existing methane by lowering the burden on atmospheric oxidants. Thus, avoiding methane emissions can lower the impact of previous methane emissions by shortening its lifetime.

“We’re over 420 parts per million of CO2 now, but methane is two parts per million. Imagine a million molecules — two of them are going to be methane. So how do you remove that dilute of a gas stream? That’s a super big challenge, not just for microorganisms, but it’s a major challenge for any technology. There isn’t a single technology that can do it, so we have to be creative in how to think about really dilute methane streams.

How can microbes play a role in methane removal solutions?

“The benefit of using microorganisms is that they are present across vast landscapes. And we know that atmospheric methane removal and growth on atmospheric methane happens [in microbes]. 

But because these are dilute energy sources, the rate of [microbe] growth and the rate of gas drawdown is quite slow. In other words, it’s not fast enough for us to see a change in the atmospheric concentration over the time interval we need to slow climate change.

So the question is, how do we harness that activity to speed it up? How can we bolster it? There’s some really good ideas around how to do that, and I think we’re getting some great technology started up.”

What else do we need to consider when thinking about climate change microbiology and greenhouse gas removal?

“In Alberta, and in the other countries as well, we’re putting billions of dollars into making hydrogen a new green energy source. The big issue with hydrogen in the methane sphere — and this touches on how these gasses interact — hydrogen, when it goes into the atmosphere, reacts with hydroxyl. 

The problem is that hydroxyl reacts with methane in the atmosphere as the major global sink. The reason that methane is short-lived is because of the hydroxyl concentration in the atmosphere. If hydrogen removes that sink, then the methane has nothing to react with and now methane becomes a long-lived greenhouse gas.

We have to really consider, with new energy sources, these things are all dynamically interacting with each other and they all have the same types of chemistry or similar types of chemistry sinks … So how do we manage that? We’re not going to just switch energy sources and voila, we’re finished. There’s consequences.

Redox [oxidation-reduction reactions] is absolutely vital to understand when we’re talking about any type of greenhouse gas dynamics. And that goes for all of the greenhouse gasses in a metabolic context, and even in a chemical context.”

How does the linkage between nitrous oxide and methane work?

“In my graduate work, I was looking at the enzymes leading to nitrous oxide. I didn’t actually know that there was a link [to methanotrophs] until I’m like, huh they have all of these enzymes in common. I wonder if methanotrophs also make nitrous oxide similar to the way that the ammonia oxidizers do.

Methanotrophs are especially found in lakes that have an anoxic part of the water column. And this is where methanotrophs are thriving, but there’s no oxygen. 

And so the question in biogeochemistry was: Are they oxidizing methane? They’re not breathing, they don’t have oxygen. And it turns out, they’re breathing nitrate. This is in lakes that have enough nitrate that it becomes [the methanotrophs’] electron acceptor instead of oxygen, and their product is nitrous oxide. That paper was published in 2015, but there are papers that report this activity all over the world.”

How can we control some of the negative effects of greenhouse gasses like nitrous oxide and methane? 

“It’s a great interconnected web out there. We can’t just look at one process or one group of microbes and think that’s it and that’s going to be how we solve the problem … In reality, in ecosystems, they are all cross feeding each other, interacting in ways that we don’t completely understand.

What I would challenge this community to think about is [this]: When we are modifying nutrient additions to an ecosystem or augmentations to an ecosystem to promote a particular activity, we need to understand how that’s changing and altering activities downstream.”

Learn more about Dr. Stein’s work 

Read Professor Stein and Professor Lidstrom’s new Science piece on why we should look at methane and nitrous oxide simultaneously.

Professor Stein’s 2019 lecture “Methane! It’s more than a gas” and 2016 Primer on the Nitrogen Cycle is probably the best materials you can read and reference if you’re going to work on nitrogen challenges.

Stay up-to-date on Professor Stein’s research in climate change microbiology.

Researchers and work mentioned in the podcast

Lisa Stein

Professor, University of Alberta and Canada Research Chair for Climate Change Microbiology

  • Researcher of microbial interactions in methane and nitrogen cycles, atmospheric methane removal, and benthic methane emissions from lakes and wetlands.
  • Co-authored a publication in Science with Mary Lidstrom on methane and nitrous oxide.

Ralph Conrad

Professor Emeritus, Max Planck Institute for Terrestrial Microbiology

  • A notable researcher in the field of microbial methane and nitrous oxide interactions.
  • Provided feedback on early PCR work related to methanotrophs and denitrification.

Mary Lidstrom

Professor Emeritus of Chemical Engineering and Microbiology, University of Washington 

  • Researcher working on methanotrophs that grow on very low methane concentrations.
  • Co-authored a publication in Science with Lisa Stein on methane and nitrous oxide.

Alexander Tveit

Associate Professor, UiT, The Arctic University of Norway

  • Works with methanotrophs and their natural ability to grow on low methane concentrations.

Rob Jackson

Professor and Senior Fellow, Stanford University

  • Uses satellite observations to study methane sources, particularly around the Arctic.

Whendee Silver

Professor of Ecosystem Ecology and Biogeochemistry, UC Berkeley

  • Measuring small fluxes of greenhouse gasses like methane, CO2, and nitrous oxide from soils and trees.

Karen Lloyd

Professor of Earth Sciences, University of Southern California

  • Studied methanogenesis deep underground, including in environments like South African gold mines.

Other Mentioned Concepts:

  • Benthic Methane: Contribution of methane from hydroelectric dams and lakes, estimated at gigatons per year in CO2 equivalents.
  • Nitrogen Cycle: Complex interactions involving nitric oxide and nitrous oxide, including their toxic effects and their use in medical treatments like Viagra.
  • Methanotrophic Bioreactors: Potential for large-scale use in atmospheric methane removal, involving augmentation and creating more surface area for microbial activity.
  • Enzyme Activities: Mentioned work on synthetic catalysts and nitrogenase, with a call to industrial chemists to explore microbial enzyme activities for industrial applications.
By Homeworld Collective