Bacterial growth could reveal Earth’s origins

For years, geologists have analyzed microbes to decipher how cells functioned 3 billion years back.

Last Updated: May 18, 2010, 14:17 PM IST

Washington: For years, geologists have analyzed modern microbial mats to decipher how cells functioned as far back as 3 billion years.
Now, researchers have found a way to garner new information from cells by linking the even spacing between the thousands of tiny cones that dot the surfaces of stromatolite-forming microbial mats.

Nutrient-exchanging bacteria grow mostly on moist surfaces and collect dirt and minerals that crystallize over time.

Stromatolites are the bacteria that turn to stone just beneath the crystallized material, thereby recording their history within the crystalline skeletons.

They are considered to be the oldest fossils on Earth with patterns that also appear in cross-sectional slices of stromatolites that are 2.8 billion years old — to photosynthesis.

Scientists at MIT``s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and the Russian Academy of Sciences suggest that the characteristic centimeter-scale spacing between neighboring cones that appears on modern microbial mats and the conical stromatolites they form occurs as a result of the daily competition for nutrients between neighboring mats.

By analyzing the length of the triangular patterns seen in an ancient stromatolite, for example, geologists can now infer more details about the environment in which the microbial mat lived, such as whether it lived in still or turbulent water.

The scientists proposed that the pattern was not coincidental and could pertain to a biophysical process, such as how the bacteria compete for nutrients.

By studying photosynthesis, they formed a better understanding of how a mat consumes nutrients from its surroundings over the course of a day, and then metabolizes, or breaks down, those nutrients for energy.

It takes in nutrients like inorganic carbon from its immediate surroundings and uses energy from sunlight to build sugars and new bacteria.

As these nutrients become locally depleted, the mat starts to consume nutrients from larger distances.

At nighttime when it is dark and photosynthesis is not possible, nutrients return to the water immediately surrounding the mat.

The researchers reasoned that in order to avoid direct competition for nutrients, the spacing between mats must be influenced by diffusion, or how molecules spread out over time.

In this case, diffusion is itself influenced by the amount of time a mat is metabolically active, which varies over the course of a day due to changes in sunlight. Therefore, the spacing between cones records the maximum distance that mats can compete with one another to metabolize nutrients that are spread by diffusion and later replenished at night.

After testing this theory on cultures in the lab, the researchers confirmed their hypothesis through fieldwork in Yellowstone, where the centimeter spacing between mats corresponds to their metabolic period of about 20 hours.

That the spacing pattern corresponds to the mats`` metabolic period — and is also seen in ancient rocks — shows that the same basic physical processes of diffusion and competition seen today were happening billions of years ago, long before complex life appeared.

The study has been published in the Proceedings of the National Academy of Science. (