Researchers Break New Ground in Their Study of Bacteria

Melissa Lage and Jennifer Hughes found that bacteria follow what ecologists call the "species-area relationship."

by Wendy Y. Lawton

Bacteria are the most common organisms on earth. They can be found in Arctic ice and hot springs, inside rocks and animal guts, in pristine meadows and polluted ponds. There are too many kinds of bacteria to count, although one estimate puts the figure as high as 100 billion.

Bacteria are so varied and ubiquitous, they've spawned this scientific saying: "Everything is everywhere." But the world of these single-celled creatures isn't as chaotic as previously thought, according to a groundbreaking experiment conducted by a pair of Brown evolutionary ecologists.

Melissa Lage (standing) and Jennifer Hughes (foreground), along with colleagues at Stanford University and the University of Washington, found that bacteria follow what ecologists call the "species-area relationship." This is the logical notion that the number of species in an area increases as the size of the area increases. Put another way, the number of species in a 100-acre swath of forest is greater than the number found among a single stand of trees.

Their work, published in the December 9 issue of Nature, is the first to show that this basic law of nature holds true for bacteria. Another article in the same issue showed that fungi also follow this rule.

Lage, a graduate student pursuing a doctorate in ecology and evolutionary biology, and Hughes, Manning Assistant Professor in the department, said the findings give scientists a new understanding of these microscopic organisms.

"Bacteria respond to their environment," Lage said. "If there are changes in the environment, there may be changes in the kinds of bacteria we see."

Given the critical role bacteria play in the global ecosystem, this is an important notion. Bacteria purify water, pump oxygen into the air, and decompose dead plants and animals. Now scientists know that different bacteria may perform these functions differently, depending on the place.

"For example, a salt marsh in Rhode Island may behave differently in terms of how it buffers Narragansett Bay from nitrogen pollution than a similar-looking marsh in San Francisco," Hughes said.

But the work has other implications.

If the environment changes due to pollution or global warming, bacteria change, too. This makes the effects of environmental change less predictable, Hughes said. For example, how does global warming change the rate of decomposition? It's not an idle question. Decomposition pumps carbon dioxide into the atmosphere, a task critical for photosynthesis. No photosynthesis, no plants. No plants, no food.

Lage and Hughes conducted their experiment in a half-acre of salt marsh on Prudence Island, just a quick ferry ride from Bristol. Using a carefully measured grid, they took twenty-six one-gram samples of soil. "Very muddy process," Lage said.

The mud, however, was a small hurdle. How do you count organisms so small that some can't even be seen by microscope? You can't. Instead, you do a lot of heavy lifting in the lab. Lage used a kit to extract DNA from each sample. A machine then amplified only bacteria from DNA, which was cloned and cultured in E. coli. Then Lage randomly tested each of the twenty-six plates and counted the different types, using their unique gene sequences.

The findings: Bacterial communities were very similar a couple of centimeters apart, but more different hundreds of meters apart. Bottom line: Bacteria aren't randomly distributed, but follow the same ordered pattern of distribution as plants and animals.

The importance, and mystery, of bacteria astounds both scientists. Hughes will continue to study these ancient organisms. Last year, she won a prestigious grant from the National Science Foundation to conduct a global study of bacteria in coastal marshes, one of the most threatened ecosystems in America.

"Because we know so little about the ecology of bacteria," she said, "we're set for research for the next couple decades."