ASBMB Annual Meeting

Kountz tracks methyls in microbe metabolism

Meet a JBC Herbert Tabor Early Career Investigator Award winner
Courtney Chandler
March 12, 2021

Duncan Kountz became interested in microbial biochemistry through a seemingly standard source: a textbook. But this wasn't a textbook assigned for class or research — he chose it himself because it seemed interesting, a habit he started in high school.

Duncan Kountz

"Textbooks help me expand what I'm exposed to," Kountz said, "and I find them perfectly tolerable as long as they're on a subject I'm interested in."

The habit helped him prepare for a career in science, which he knew he wanted to pursue from the time he was in high school. Following a family legacy, he attended Ohio State University and sought research opportunities. He started out in a developmental biology lab, but that textbook, "The Physiology and Biochemistry of Prokaryotes," inspired a move to microbial metabolism. He contacted Joseph Krzycki, an OSU researcher in the field, and joined Krzycki's lab as a sophomore.

"Complexity and diversity really interest me, and I found that in microbial physiology, those are both on display," Kountz said. "Microbes may seem like they're a simple system, but they're also amenable to detailed work."

The Krzycki lab was finishing a project on an enzyme belonging to a superfamily of methyltransferases, and Kountz wanted to investigate similar enzymes in the context of the gut microbiome. He observed that a particular gut bacterium, Eubacterium limosum, encoded many of these enzymes and could utilize several unusual molecules for its growth. He focused on one in particular, carnitine, and tracked down the enzymes responsible for its metabolism.

His research shows how microbial metabolism can affect both microbial prosperity and the health of the human host, as carnitine metabolism can produce toxic byproducts. Kountz was excited about the findings, in part for this potential real-world applicability.

"I think we are really at the dawn of using microbes to solve problems," he said. "I'm excited about the idea of engineering or finding new microbes with interesting properties that we can exploit to make human life better."

Now a fourth-year Ph.D. student in Emily Balskus' lab at Harvard, Kountz said his textbook count currently exceeds 100.

Methyl-removing enzyme diverts toxin precursor

Gut bacteria can produce harmful compounds as a byproduct of their normal metabolism. Carnitine, a quaternary amine found abundantly in red meat, can lead to production of a toxin precursor called trimethylamine, or TMA, during digestion. TMA is converted in the liver to TMA oxide, a marker of cardiovascular disease.

Duncan Kountz and colleagues at Ohio State showed that the gut bacteria Eubacterium limosum can use carnitine as fuel, thereby potentially curbing TMA production. They also identified a new metabolite, called norcarnitine, produced by demethylation of carnitine.

Seeking to identify the enzymes involved in this metabolic transformation, Kountz noticed that E. limosum encoded many enzymes in the MttB superfamily. MttB proteins are involved in methyl transfer reactions.

Kountz characterized the enzymes involved in this pathway and identified a methyltransferase, MtcB, that demethylates carnitine and shuttles the product into pathways responsible for energy utilization and biogenesis.

The study highlights how metabolic activities in gut microbia may promote health by preventing production of toxin precursors.

Enjoy reading ASBMB Today?

Become a member to receive the print edition monthly and the digital edition weekly.

Learn more
Courtney Chandler

Courtney Chandler is a biochemist and microbiologist in Baltimore, Md., and a careers columnist for ASBMB Today.

Get the latest from ASBMB Today

Enter your email address, and we’ll send you a weekly email with recent articles, interviews and more.

Latest in People

People highlights or most popular articles

'Give yourself grace'

'Give yourself grace'

July 1, 2022

Our careers columnist interviewed Robyn Sellers about teaching and doing outreach through a science center.

A youthful goal blocked by power failures
BMB in Africa

A youthful goal blocked by power failures

June 30, 2022

ASBMB member Isa Joseph Danladi faced challenges in his final research project at Kaduna State University in Nigeria.

A medical student with a community mindset
BMB in Africa

A medical student with a community mindset

June 29, 2022

Mustapha Aminu, an ASBMB member in Ghana, serves his community through creative problem-solving.

Seeing what I become: An academic journey
BMB in Africa

Seeing what I become: An academic journey

June 28, 2022

“As the oldest child, I made up my mind to go to school and make it in life so I could take care of my parents and siblings.”

2022 honor society inductees
Student Chapters

2022 honor society inductees

June 27, 2022

Chi Omega Lambda recognizes exceptional undergraduate juniors and seniors who are Student Chapter members.

Nights and days in the lab
BMB in Africa

Nights and days in the lab

June 23, 2022

With help from colleagues, mentors and others, Oluwaseyefunmi Adeniran pursues her dream of making scientific discoveries that improve human health.