Human World

Justin Gallivan engineers bacteria to destroy a harmful pollutant

Justin Gallivan: I’m interested in programming bacteria much as you would program a computer.

Justin Gallivan is a chemist at Emory University, and a recipient of many awards including being named a Sloan Fellow and most recently a 2010 Pop Tech Science Fellow. Dr. Gallivan is working on engineering bacteria to seek out and destroy harmful chemicals in our environment.

Justin Gallivan: All living things execute chemical programs that are encoded in their DNA. If you change the DNA, you can change the behavior.

Gallivan introduces new DNA into bacteria. He said his technique is similar to cutting and pasting on a computer and it lets him select the tasks for the bacteria to perform. In this case, the bacteria’s target is Atrazine, a widely-used agricultural chemical that can contaminate public water supplies.

Justin Gallivan: What we did was we developed a chemical switch, known as a riboswitch, that turns genes on in the presence of Atrazine.

Gallivan said the introduced genes direct the bacteria to move towards the Atrazine molecule and then break it down, effectively destroying it. He said the goal is to release the bacteria into a polluted environment, have them seek out and destroy the Atrazine, and then die, with no additional impact on the environment. He said they’ve tested the reprogrammed bacteria only in the lab so far. Meanwhile, the U.S. government commissioned a report from a panel of experts to assess the risks of releasing engineered bacteria into the environment – and make recommendations on how to regulate this new type of bacteria and new way of battling contaminated public water supplies.

Justin Gallivan: We’re trying to demonstrate the larger point that yes, we can program bacteria to perform complex tasks, and these complex tasks can be quite useful, in hopefully, one day addressing an important environmental challenge.

Gallivan said bacteria don’t require a lot of new information in order to perform new tasks.

Justin Gallivan: There are two steps. To introduce new DNA into bacterium actually involves essentially a cutting and pasting mechanism. We can cut out small pieces of DNA using molecules known as restriction enzymes. We cut them at specific sites. Then using other enzymes we can paste them into the bacterium – so we’ve inserted new DNA into the organism.

The bacterium can then replicate the new DNA on its own.

Justin Gallivan: Now we need to find other ways to turn those genes that the DNA encodes, on and off when we want to. The way my lab has been pursuing involves a chemical cousin of DNA, which is RNA. RNA is a molecule found in you and me. One of the amazing things that it can do is bind to other molecules, essentially giving them a bear hug. We add the particular molecule we are interested in, it can bind to that RNA molecule, that RNA undergoes a change in its shape, and that leads to a change in whether the gene is on or off.

Gallivan published a paper in May 2010 demonstrating this principle, applied to the chemical Atrazine. But he said that the bacteria are still too weak to effectively combat Atrazine in the environment.

Justin Gallivan: Currently we have to add relatively high concentrations of Atrazine to get the system to work. We would like to make it better so that the cells don’t need as much Atrazine to respond to it. We’d like to make the cells work more quickly than they currently do. And we’d like to make the cells more robust as well.

Speaking of the release of the engineered bacteria into the environment, Gallivan said those bacteria made in a lab are generally not able to compete with bacteria that have evolved to survive in a natural environment.

Justin Gallivan: The big challenge going forward would be to find bacteria that actually can compete so they can complete their task before they die out.

Justin Gallivan is a 2010 Poptech Science and Public Leadership Fellow, addressing a need for socially engaged scientists as public communicators.

December 20, 2010
Human World

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