Originally created 08/29/98

Study finds prokaryotes populate Earth



ATHENS, GA. -- It's probably best not to interrupt William Whitman when he works.

In his latest project, the University of Georgia microbiologist led a team that counted the number of bacteria on Earth.

After a year of counting, he estimates the number to be five million trillion trillion. Or thereabouts.

That's a five followed by 30 zeros.

"I was actually surprised that the number was so high," Whitman said.

High indeed.

If each bacterium were a penny, the stack would reach a trillion light years, which is the distance a ray of light travels in a year, moving at about 186,000 miles a second. The number dwarfs the size of the human population, or even the insect population. The count might even scare the microbe-wary of this planet, but Whitman said it shouldn't.

"Most bacteria are actually very good," he said.

For the first-ever study, published recently in the "Proceedings of the National Academy of Sciences," Whitman and co-authors David Coleman of the UGA Institute of Ecology and William Wiebe of the UGA Department of Marine Sciences compiled a list of habitats where bacteria -- or prokaryotes -- abound in the Earth's subsurface, soil, oceans, air and animal insides.

Then they researched previous counts in habitats in their quest to estimate a total number.

Why bother to count to a nearly incomprehensible number?

"There simply hadn't been any estimates of the number of bacteria on Earth," Whitman said. "Because they are so diverse and so important, we thought it made sense to get a picture of their magnitude."

"We estimated that about 92 to 94 percent of the Earth's prokaryotes are in the soil subsurface," he said. "It had been estimated that before that one-half of the living protoplasm on Earth is microbial, but our new figures indicate that this estimate is probably much too conservative."

The study could open new areas of inquiry, especially about the rate of mutations and how bacteria operate in nature.

Scientific novices need not fear the high number of bacteria, Whitman said. The microbes not only cause disease, but also increase nitrogen in the soil and promote a healthy, beautiful planet, among myriad purposes.

As a result of the study, the team of researchers now find their hands full seeking another staggering figure: the number of bacterial species.