The world inside a bacterium
Posted: Thursday, June 05, 2008 6:25 PM by Alan Boyle
Pantheon Books |
"Microcosm" focuses on
E. coli and the new
science of life.
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Can a whole book actually be written about one single-celled organism? "Microcosm" pulls off the feat by using the E. coli bacterium as a guidepost to life's secrets.
E. coli? Isn't that one of the biggest villains of the bacterial world? The one responsible for the spinach scare and last year's tainted-beef recall? Yes, those problems were caused by bad breeds of E. coli - but for every bad strain, there are hundreds of good strains you can't live without.
"You have several billion E. coli inside of you right now, and they're going to be with you until you die," science writer (and blogger) Carl Zimmer told an audience at Town Hall Seattle this week, capping a West Coast book tour for "Microcosm."
Over the years, Zimmer has written about subjects ranging from zombie cockroaches to species-hopping to the seat of the soul - and when he started formulating the plan for his latest book, he wanted to address one of the world's greatest mysteries: What is life, and how does it work?
That subject is just a teensy bit too broad for one book, however. So Zimmer looked for a way to scale his scope back, and address the what-is-life question in a microcosm - literally, a cosmos on a microscopic scale. And E. coli was the obvious choice. Zimmer took his lead from Nobel-winning biologist Jacques Monod, who once said, "What is true for E. coli is true for the elephant."
E. coli is the Joe Six-Pack of the microbial world: German-Austrian pediatrician Theodor Escherich found it in 1885 as he rooted through baby diapers, looking for the causes of infectious disease. (The "E" in E. coli stands for Escherichia, a genus name that honors the discoverer.)
Escherich and the researchers who followed in his footsteps found that E. coli could live on all sorts of things - milk, potatoes, blood - and could survive under a wider range of conditions than most microbes. Starting in the 1930s, it became the microbial model of choice for experiments aimed at figuring out how genes worked.
Genetic 'gold standard'
Today, E. coli is "the gold standard of genetic familiarity," Zimmer writes. Scientists know more about how E. coli works than about virtually any other living thing.
Ben Stechshulte |
Carl Zimmer uses E. coli as a microcosm of all biology.
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Even though it's just a one-celled organism, the darn thing has a molecular sense of smell that passes along a signal that food is nearby - and it has a system for getting to that food, by whipping its tails around in particular patterns that semi-randomly get it where it needs to go.
Those tails - also known as flagella - have even contributed to a cultural controversy over evolutionary theory vs. intelligent design. How could undirected evolution ever produce those tricky whips, which seem to work like tiny outboard motors? The flagellum became a hot topic during 2005's Dover evolution trial - and was cited in the judge's ruling against intelligent design.
Zimmer addresses the courtroom case in "Microcosm," as well as the way E. coli supports the case for evolution in the laboratory. The bacterium has proven so adaptable to changing conditions that scientists are able "to put natural selection under a microscope, teasing apart the individual mutations that benefit E. coli," Zimmer writes.
One of the longest-running experiments is being conducted by Richard Lenski and his colleagues at Michigan State University. For 20 years, Lenski has let E. coli run its course over 44,000 bacterial generations in the lab. He freezes samples every 500 generations, and keeps careful track of how the bacteria cope with a low-glucose diet.
CDC |
E. coli bacteria quickly form
colonies when they are smeared
across the goo in a petri dish.
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Just this week, Lenski published findings about a bizarre twist that is described in Zimmer's blog: Even under the carefully controlled lab conditions, one bacterial strain gained the ability to digest citrate - something that E. coli isn't supposed to be able to do.
The researchers were able to run the tape backwards, checking exactly when the citrate-munching bugs learned the trick. At the 31,500-generation mark, they found that about 0.5 percent of the bacteria could consume citrate. That population grew for a while, then was almost rendered extinct, and then came back with a vengeance to dominate the entire flask.
The assumption is that one genetic mutation provided a relatively poor method for digesting citrate, and that a later mutation provided the full recipe for success. Zimmer said E. coli's chances of evolving into a citrate-eater were on the order of 1 in a trillion - and yet, it happened.
"It may not be the origin of new species, but it's a major transition," Zimmer said.
Pushing forward
E. coli could serve not only as a tool for looking backward at evolution's course, but also as a tool for pushing forward on medical and technological challenges.
Genetically modified E. coli is already being used to manufacture human insulin, and Zimmer describes efforts to turn the bacteria into photographic film, anti-cancer "torpedoes" and biofuel factories. They can also be transformed into microscopic computers for solving sticky math problems.
Scientists have even tweaked E. coli in the lab to use amino acids that are not used by any other type of living organism. "In a sense, we've actually created alien life on Earth," Zimmer said.
E. coli and its ilk could eventually help scientists answer more of those cosmic questions:
Zimmer doesn't downplay the possibilities.
"Jacques Monod said, 'What is true for E. coli is true for elephants.' I wonder if it's true for aliens," he said.
"E. coli is already up in space, it's in the space station. So if you look up and look at the space station at night, you'll be looking at E. coli. I don't think that when and if we get to Mars, we will discover E. coli on the Red Planet. But I do wonder if there will be some striking similarities between the Martians and this really remarkable microbe."
For more about "Microcosm," check in with Carl Zimmer's Web site and the ScienceBlogs Book Club. Real Science has the complete podcast of Zimmer's talk in Seattle.
