Catherine Drennan - Enlisting microbes to solve global problems
Researchers harness bacteria to produce energy, clean up environment
Anne Trafton, News Office
February 17, 2009
In the search for answers to the planet's biggest challenges, some MIT
researchers are turning to its tiniest organisms: bacteria.
The idea of exploiting microbial products is not new: Humans have long
enlisted bacteria and yeast to make bread, wine and cheese, and more
recently discovered antibiotics that help fight disease. Now, researchers in
the growing field of metabolic engineering are trying to manipulate
bacteria's unique abilities to help generate energy and clean up Earth's
MIT chemical engineer Kristala Jones Prather sees bacteria as diverse and
complex "chemical factories" that can potentially build better biofuels as
well as biodegradable plastics and textiles.
"We're trying to ask what kinds of things should we be trying to make, and
looking for potential routes in nature to make them," says Prather, the
Joseph R. Mares (1924) Assistant Professor of Chemical Engineering.
She and Gregory Stephanopoulos, the W.H. Dow Professor of Chemical
Engineering at MIT, are trying to create bacteria that make biofuels and
other compounds more efficiently, while chemistry professor Catherine
Drennan hopes bacteria can one day help soak up pollutants such as
carbon monoxide and carbon dioxide from the Earth's atmosphere.
Found in nearly every habitat on Earth, bacteria are chemical
powerhouses. Some synthesize compounds useful to humans, such as
biofuels, plastics and drugs, while others break down atmospheric pollutants. Most rely on carbon compounds as an energy source, but
species differ widely in their exact metabolic processes.
Metabolic engineers are learning to take advantage of those processes,
and one area of intense focus is biofuel production. At MIT, Prather is
developing bacteria that can manufacture fuels such as butanol and
pentanol from agricultural byproducts, and Stephanopoulos is trying to
make better microbial producers of biofuels by improving their tolerance to
the toxicity of the feedstocks they ferment and products they make.
The recent spike in oil prices and growing greenhouse-gas emissions have
catalyzed the push to find better pathways to produce biofuels and other
chemicals such as bioplastics. "You see a visible boost when you have a
crisis linked to energy problems," says Stephanopoulos.
Manufacturing plastics and textiles using bacteria can be far less energyintensive
than traditional industrial processes, because most industrial
chemical reactions require high temperatures and pressures (which require
a great deal of energy to create). Bacteria, on the other hand, normally
thrive around 30 degrees Celsius and at atmospheric pressure.
Metabolic engineering involves not only creating new products but also
developing more efficient ways of making existing compounds. Recently,
Prather's laboratory reported a new way to synthesize glucaric acid, a
compound with multiple uses ranging from the synthesis of nylons to water
treatment, by combining genes from plants, yeast and bacteria.
Prather is also working on bacteria that transform glucose and other simple
starting materials into compounds that can be used to make biodegradable
plastics such as PHA (polyhydroxyalkanoate). In Stephanopoulos'
laboratory, researchers are developing new ways to produce biodiesel,
plus other compounds including the amino acid tyrosine, a building block
for drugs and food additives; biopolymers and hyaluronic acid, a natural
joint lubricant that can be used to treat arthritis.
Both labs collaborate in a project to engineer the isoprenoid pathway in
yeast and bacteria, which is responsible for the biosynthesis of many
important pharmaceutical compounds. The two labs are investigating
methods to make different compounds with higher activity as well as
Microbes express a huge range of metabolic pathways, offering great
opportunities but also challenges. "Biology has a lot of diversity that's
untapped and undiscovered, but the flip side is that it's hard to engineer in
precise ways," says Prather. "Nature has evolved to do what it does, and to
get it to do something different is a nontrivial task."
Bacterial cleanup crew
Drennan is also looking to bacteria, but with a different goal in mind.
Instead of using bacteria to build things, she's studying how they break
things down -- specifically, carbon dioxide, carbon monoxide and other
Her microbes, found in a range of habitats including freshwater hot springs,
absorb carbon dioxide and/or carbon monoxide and use them to produce
energy. Such microbes remove an estimated one billion tons of carbon
monoxide from Earth and its lower atmosphere every year.
"These bacteria are responsible for removing a lot of CO and CO2 from the
environment," says Drennan, who is a Howard Hughes Medical Institute
investigator. "Can we use this chemistry to do the same thing?"
To answer that question, Drennan and her students are using X-ray
crystallography to decipher the structures of the metal-protein enzymes
involved in the reactions, which they believe will allow them to figure out
how the enzymes work. That understanding could lead to development of
catalysts to lower carbon monoxide levels in heavily polluted areas.
"If you're going to borrow ideas from nature, the first step is to understand
how nature works," she says.
A version of this article appeared in MIT Tech Talk on February 25, 2009. MIT News article.