Microbiologist Thomas Brock, whose bacterial discovery led to the creation of a transformative technique for molecular biology, died on April 4 at the age of 94. Brock’s wife Katherine tells The New York Times that the cause of death was complications after a fall.

Born in 1926, Brock grew up in Ohio near Lake Erie and developed a love of the natural world early on. His parents supported his scientific curiosity, and after spending a year in the US Navy during World War II, he attended the Ohio State University for a bachelor’s in botany, then earned a master’s and PhD in mycology, also at Ohio State.

After working for a few years in industry, Brock accepted a teaching position at Indiana University in 1960. In 1964, his field studies took him to Yellowstone National Park, where he was immediately drawn to the microbes living...

“I got out of the car and, by chance, a ranger was giving a talk near a thermal pool,” Brock later recalled in an interview with the National Park Service. “I saw all this color, and he said it was blue-green algae. I got interested right away.”

Brock returned to Yellowstone over the next few years to better understand its microbial life, and in 1966 identified a bacterial species he named Thermus aquaticus, which lived at temperatures of around 70 °C. The following year, Brock published his observations about life in hot springs in Science, challenging the assumption of the day that life couldn’t exist at temperatures that high.

“It is thus impossible to conclude that there is any ‘upper temperature of life,’” Brock wrote in the paper.

In 1976, cell biologist Alice Chien discovered Taq, an enzyme that T. aquaticus uses to replicate its DNA in high temperatures. A decade later, biochemist Kary Mullis used Taq to create polymerase chain reaction, or PCR. PCR relies on thermal cycling to copy DNA and amplify certain genes if they are present in a sample. It is one of the most widely used techniques in molecular biology and biomedical research and is the basis for gold-standard tests for COVID-19. In 1993, Mullis shared the Nobel Prize in Chemistry with Michael Smith for developing PCR.

In 1971, Brock left IU for the University of Wisconsin–Madison, where he would remain until his retirement in 1990. For three years in the 1980s, he served as the chairman of the department of bacteriology. He wrote many books on microbiology.

In his retirement, he and his wife created the Pleasant Valley Conservancy State Natural Area on 140 acres in Wisconsin. In addition to preserving the area’s wilderness, Brock also wanted to use the site to better understand the decline of oak barrens throughout the Midwest.

“He had an encyclopedic knowledge of microbiology and science in general,” Stephen Zinder, a microbiologist who trained under Brock during the 1970s, tells the Times. “I think his real ability was to see things simply and to figure out simple techniques to find out what the organisms were doing in their environment.”

Brock is survived by his wife Katherine, daughter Emily, and son Brian.

Thomas Brock recalls his discovery of Thermus aquaticus and its later impact on the development of PCR.
University of wisconsin–madison

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Dr. Brock standing in nature, holding a walking stick and wearing binoculars around his neck.

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