A single-celled microbe that lives in our guts has been linked to a number of health conditions that can be tough to treat: type 2 diabetes, weight gain, obesity, and irritable bowel syndrome (IBS), as well as constipation and bloating.

Its name is Methanobrevibacter smithii. M. smithii for short.

Or, as Dr. Ruchi Mathur sometimes calls it, "that little guy."

It's all right for them to be on a nickname-basis. She's been studying this single-celled troublemaker and its role in the microbiome for over 5 years. And yet she and her colleagues are quick to defend the little bug.

"It's not as simple as 'M. smithii is just bad,'" says Chandrima Chatterjee, a research coordinator in the Medically Associated Science and Technology (MAST) Program.

"Like most of the microbiome, it's not a clear-cut distinction of good guy versus bad guy. It's about the balance, and every individual is different."

We all have trillions of microorganisms living in our bodies, Chandrima explains.

They're from thousands of different species and they make up our microbiome, the internal ecosystem of our bodies. Studying the role that all these microbes play—bacteria, fungi, viruses, and others—in our health has become a big field in medical research.

M. smithii is an archaea, a type of single-celled organism that doesn't have a distinct nucleus. It's one of the most common microbes living in our guts.

On the most basic level, it produces methane.

When we eat starchy foods like bread or potatoes, our gut microbiomes get to work digesting.

That creates hydrogen and carbon dioxide gas. Part of that hydrogen is gobbled up by M. smithii, which then produces methane.

The methane can be exhaled on your breath, eliminated in your stool, or absorbed into your blood.

Some people have higher concentrations of this methane-producer in their guts than others and they tend to be at higher risk of obesity and constipation-predominant IBS.

There's also a growing number of studies that suggest M. smithii and other archaea affect metabolism and can cause weight gain.

And it can affect how well your body absorbs sugars—also known as glucose tolerance. Impaired glucose tolerance is a sign that someone could develop diabetes.

This is just one microbe in the microbiome the MAST program is looking at to better understand how these tiny organisms we live with play a role in our health.

We frequently talk about precision medicine, and we think understanding the makeup of the microbiome will play an important role in treating some health conditions.

In 2016, MAST published a study with people who are obese and have prediabetes; reducing the participants' M. smithii levels with an antibiotic made a difference. They lowered their overall cholesterol levels, and their glucose and insulin levels improved.

It was the first time anyone showed that lowering methane levels through antibiotic therapy led to those improvements.

Our group continues to study M. smithii and the overall gut microbiome and the role of microbes in diagnosing and treating conditions like obesity, diabetes, and IBS.

It's just the beginning. We're hopeful that understanding M. smithii's role will lead to better treatments for some difficult health problems.