ATHENS, Ga. -- They're everywhere. Bacteria are the huddled masses of the microbial world, performing tasks that include everything from causing disease to fixing nitrogen in the soil. Now, for the first time, a team of researchers from the University of Georgia has made a direct estimate of the total number of bacteria on Earth -- and the number makes the globe's human population look downright puny.
The group, led by microbiologist William. B. Whitman, estimates the number to be five million trillion trillion -- that's a five with 30 zeroes after it. Look at it this way. If each bacterium were a penny, the stack would reach a trillion light years. These almost incomprehensible numbers give only a sketch of the vast pervasiveness of bacteria in the natural world.
"There simply hadn't been any estimates of the number of bacteria on Earth," said Whitman. "Because they are so diverse and important, we thought it made sense to get a picture of their magnitude."
The study was published in June in the Proceedings of the National Academy of Sciences and was funded in part by grants from the National Science Foundation and the U. S. Department of Energy. Co-authors of the paper from the University of Georgia were Dr. David Coleman of the Institute of Ecology and Dr. William Wiebe from the department of marine sciences.
When people think of bacteria, they likely first consider the nasty ones that cause disease, but the bacteria inside all animals combined -- including humans -- makes up less than one percent of the total amount. By far the greatest numbers are in the subsurface, soil and oceans.
Scientists prefer to call bacteria "prokaryotes," a term that describes a single-cell organism without a nucleus. Prokaryotes are extraordinarily diverse and range from plant-like cells that produce molecular oxygen in the oceans to soil-borne bacteria responsible for fertility.