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Slime mold farmers.

When we think about agriculture, we think about farmers--usually human farmers. We think about tilling the soil, planting seeds, watering seedlings and harvesting crops: things done by human farmers, on farms.


Humans, however, aren't the only living things that farm. Some types of ants, termites, snails and beetles have been observed to practice agriculture. A new study adds an even more surprising kind of farmer to that list: amoebas. An amoeba is a (usually) single-celled organism that looks like a blob, with one or more nuclei inside.

According to researchers from Rice University in Houston, some types of an amoeba called Dictyostelium discoideum practice a simple type of farming--carrying "seeds" and then planting them--with their favorite food, bacteria.

These tiny farmers, sometimes called Dicty for short, live in the soil. They're also called slime molds. When there are plenty of edible bacteria around, the amoebas ooze around and dine by themselves. But when food is scarce, the amoebas become social. "They start talking to each other," Debra A. Brock told Science News. Brock, a molecular biologist at Rice, worked on the study on amoeba farmers.

The amoebas find each other and merge, becoming a single slug made of tens of thousands of individual amoebas. "It's very entertaining to watch," Brock said.

This slug can grow a slender stalk that resembles an odd mushroom. The stalk supports a round structure called a sorus, and the sorus contains spores. Spores are like seeds that can grow into new amoebas. When the spores leave the slug, they can move away to grow new organisms.

The stalk and sorus also play important roles in the amoeba farms. When the amoeba farmers are eating bacteria, they stop before they've finished. Then, like farmers collecting seeds at the end of the season, the amoebas collect the remaining bacteria. These leftover bacterial bits are packaged with the spores, in the sorus. Then, when the spores are released, so are the bacteria.

Brock and her colleagues collected 35 wild types of the creatures from soils taken from sites in Virginia and Minnesota. Back at the lab, the scientists put the amoeba samples into dishes where bacteria could easily grow.

In those dishes, amoebas that practiced farming were able to stay alive because they had brought their own food supply--in the form of bacterial bits, hidden in the spores. They were able to grow a new crop of bacteria and stay alive. The non-farmers starved in the laboratory--they had not brought their own bacteria. The scientists observed that 13 of the 35 types practice this rudimentary type of farming.

The scientists have not, however, found any evidence of an Amoeba Farmer's Almanac.


amoeba Any of various one-celled organisms that don't have a definite form. They look like tiny blobs that contain one or more center structures, surrounded by a flexible outer lining.

spore A small, usually single-celled piece of an organism that can't be ruined by getting dried out or too hot. It can grow into a new organism and is produced especially by certain bacteria, fungi, algae, and plants that don't flower.

sorus A reproductive structure in certain amoebas, fungi and lichens.

molecular biology Molecules are groups of cells, and molecular biology is the branch of biology for studying the molecules essential to life. Molecular biologists are particularly interested in how these molecules help cells reproduce and pass information on to their offspring.

* Going Deeper:

Milius, Susan. 2011. "Old Amoebas Spawn Their Farms," Science News, January 19.

Watch videos of amoeba slugs.

Sohn, Emily. 2003. "Farming on a snail's scale," Science News for Kids, December 10.
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Author:Ornes, Stephen
Publication:Science News for Kids
Date:Feb 2, 2011
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