Economists do it with spreadsheets and charts. Architects favor balsa wood. But when a biologist needs a model, it’s gotta be alive. Here’s to the tiny critters that have inched our world forward, one microscopic step at a time.

1. Big Name: Shewanella oneidensis

(Image credit: Flicker user Justin Burns)

Why It Deserves a TV Special: Shewanella can go without air longer than David Blaine. If there’s no oxygen available, this crafty bacterium can switch gears and consume metal instead. Thanks to this remarkable skill, shewanella can live almost anywhere—from the surface of the Earth to the bottom of the ocean. Not surprisingly, scientists see the bacterium as the perfect model for studying how life evolved during the early days of the Earth, when oxygen was scarce.

How It’s Saving the Planet: No one knows exactly how shewanella’s alternative breathing method works. What scientists do know is that the process transfers extra electrons to metals. When shewanella breathe in uranium and chromium (metals that can be toxic to humans), the extra electrons change the metals so that they can’t move through ground water. In other words, shewanella can actually stop toxins in their tracks. And that’s good news, because dangerous metals sometimes leak from factories and dumps, poisoning our water supplies. Because shewanella can stop these pollutants, scientists are working on ways to protect lakes and streams by surrounding toxic waste sites with the bacteria.

2. Big Name: Escherichia coli
You Know It As: E. coli

(Image credit: Flickr user Carlos Rosas)

Don’t Believe What You Read: E. coli has a reputation as the scourge of the salad bar, but the vast majority of E. coli strains won’t make people sick. In fact, E. coli is one of the most important bacteria inside your intestinal tract. Scientists love working with it, because it’s a simple organism that reproduces quickly and because it contains the component parts of more complicated life forms, such as RNA and DNA.

How It Backs Up Darwin: Believe it or not, this infamous bacterium has done a lot to further our understanding of evolution. Because of its stunning ability to reproduce quickly, E. coli is an excellent model for tracing genetic mutations. In June 2008, New Scientist reported on a research project at the University of Michigan that investigated 44,000 generations of E. coli. Twenty years ago, the researchers started with a single bacterium; then they separated its descendants into isolated populations and watched them grow. Around generation No. 31,500, one population developed the ability to metabolize citrate, a nutrient in the culture of the petri dishes. It was the equivalent of one group of people—say, Europeans—suddenly being able to digest dirt. The researchers figured this ability was based on several mutations that just happened to eventually combine into a useful trait. Try as they might, the other populations never hit on this exact combination. According to New Scientist, the experiment suggests there’s a lot of chance involved in evolution. One group can randomly develop a useful ability that the other groups never acquire, even given enough time and resources.

3. Big Name: Chlamydomonas reinhardtii
Adorable Nickname: Chlamy

(Image credit: Flickr user Orange Coast College Biology Department)

Its Place on the Family Tree: Prominent. One of the oldest forms of life, these single-cell algae live at the evolutionary branch that separates animals and plants, meaning they share characteristics with both. For instance, chlamy can transform light into energy like a plant, but it can also swim like an animal by propelling itself through water with flagella (the same wiggly tails that are attached to sperm cells). While chlamy can offer us insight into various aspects of evolution, it’s also helping us tackle human disaease. Because the algae’s flagella resemble cilia, the tiny hair-like structures that line your organs, scientists also use chlamy to model and understand the cilia’s role in illnesses such as kidney and heart disease.

How It Will Solve the Energy Crisis: One of the byproducts of chlamy’s photosynthetic process is hydrogen, an element people will need en masse to drive hydrogen-powered cars. Right now, hydrogen fuel is derived from natural gas, a non-renewable resource. Scientists are hoping that in time, however, chlamy will provide a cheaper, safer, and greener way to produce large amounts of fuel.

4. Big Name: Caenorhabditis elegans

(Image credit: Flickr user moneydick)

Why Scientists Love It: This microscopic roundworm is see-through. No, really. Thanks to its transparent flesh, biologists can easily watch what’s going on inside. And there’s a lot to see. Despite being less than 1 millimeter long, this multi-cell worm has all the physiological systems of much larger animals. Better still, 35 percent of its genes are related to ours. Another Big Advantage: C. elegans are easy to care for, needing only a petri dish for a home and E. coli to eat.

How It Will Help Us Live Forever: Scientists have used C. elegans to study what happens to individual cells and entire organisms as they age. There are two dominant theories of aging: One theory posits that aging is a cumulative process of wear and tear on cells, while the other maintains that genes control aging. A recent study of C. elegans at Stanford University provided evidence for the latter. The study found that as the worms aged, levels of three transcription factors (molecular switches that turn genes on and off) become unbalanced. These changes triggered the genetic pathways that turn spry young worms into decrepit old ones. And because it’s a lot easier to control transcription factors than it is to prevent all the things that can damage cells (injury, disease, radiation), scientists are optimistic about finding a way to keep us young forever. As Rutgers researcher Monica Driscoll told Scientific American, “Once you’ve figured out what a key molecule is doing in the worm, you can look for it in humans and expect the same things to happen.”

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The article above, written by Maggie Koerth-Baker, is reprinted with permission from the Jan/Feb 2009 issue of mental_floss magazine. Get a subscription to mental_floss and never miss an issue!

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