Planet Earth

A Better Way to Grow Cells

A 120-year-old mystery that's stumped microbiologists has been solved. 

By Lacy SchleyAug 27, 2015 12:00 AM
The vast majority of cells die off in agar growth media (left) that has been prepared traditionally by sterilizing the ingredients together. Using the new method, agar prepared with individually sterilized ingredients (right) proves much more hospitable to the cells growing within. | Y. Kamagata et al./Applied Environmental Microbiology/2014 Dec; 80(24): 7659–7666/ American Society for Microbiology

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For years, a mystery known as “the great plate count anomaly” has plagued microbiologists: Counts of living cells grown on plates in the lab aren’t as high as counts from the original sample, and no one knows why.

To grow these microorganism cultures in the lab, researchers house samples in petri dishes lined with a nourishing gel mixture derived from algae called agar growth media. But despite the nourishment, just 0.1 to 10 percent of cells make it.

The vast majority of cells die off in agar growth media (left) that has been prepared traditionally by sterilizing the ingredients together. Using the new method, agar prepared with individually sterilized ingredients (right) proves much more hospitable to the cells growing within. | Y. Kamagata et al./Applied Environmental Microbiology/2014 Dec; 80(24): 7659–7666/ American Society for Microbiology

It turns out the agar is the problem, says microbiologist Yoichi Kamagata at Hokkaido University in Japan. The standard recipes require mixing agar and phosphate solution before sterilizing them via intense heat. But Kamagata and his team realized this sequence creates hydrogen peroxide, which destroys most of the cells. Sterilize the ingredients separately, and voila, a roughly tenfold increase in cell survival rates.

“I was thinking someone else would have done this kind of experiment, as we have 120 years of agar media history,” Kamagata says. “Nonetheless, nobody cared about the media recipe.”

[This article originally appeared in print as "Recipe for Success."]

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