Illuminating dangerous pollutants

by Darryl Gebien

The same type of enzyme that enables fireflies to magically light up a dark country night could point the way to a valuable new technique for detecting dangerous pollutants in the environment. Professor Michael DuBow and his team of student researchers are engineering bacteria that glow when exposed to specific toxic agents.

These bacteria, dubbed biosensors, have the potential to be invaluable tools for probing pollution levels in water. Using the biosensors, scientists will be able to rapidly determine if a lake or river contains threatening levels of toxic substances.

"The biosensor is a sexy example of how current knowledge in genetics can be applied to the real world," says DuBow, the chair of the Department of Microbiology and Immunology.

DuBow has long been interested in how the genes of organisms are programmed to respond to changes in their environment--such as increasing levels of toxic compounds. The biosensors are a result of his research in this area, as well as an example of a new scientific approach called "ecogenetics" because it combines ecology and genetics.

The biosensors were something of an accidental discovery. DuBow and his team originally set out to determine which specific genes in simple organisms were responsible for coping with genetic toxicity. This search led to the construction of specific pollution-sensitive organisms and the realization that these creatures would make for dandy pollution-sniffers.

Bacteria were selected to serve as the model organisms for the initial response-to-toxicity study. As basic a life form as is out there, bacteria offer small, easy-to-study genetic structures.

"Because bacteria have less complex genetic systems compared to most other organisms, it's easier to study their genetic responses when they're challenged with toxic agents," says David Alexander, a PhD student working on the biosensor project.

DuBow decided to concentrate on Escherichia coli (or E. coli) bacteria since their genome had already been well characterized by other researchers and because they're relatively cheap to work with, easy to manipulate and respond quickly to changes around them.

To uncover E. coli's genetically programmed responses to elevated levels of different toxic agents, DuBow's team used gene fusion techniques. Genes called luxAB (provided to the team by biochemistry professor Ted Meighen) were randomly fused into the single chromosome of E. coli bacteria.

The luxAB gene was used because its protein product, luciferase, is responsible for the ability of fireflies and certain forms of aquatic bacteria to glow. By linking the glowing response to the expression of different genes within E. coli and then exposing the bacteria to toxic substances, DuBow would be able to determine which E. coli genes were toxicity-sensitive--they would be programmed to turn on and thus "light up" when confronted by toxic agents.

A library of 3,000 E. coli clones was created, each one containing a unique luxAB/E. coli gene fusion. It turned out that a number of the bacterial clones were sensitive to increased levels of specific toxic pollutants--one clone might glow in the presence of aluminum, while another would light up when it sensed the presence of arsenic.

Since the biosensors are sensitive to specific classes of toxins, they can give scientists a better notion of what is actually polluting a lake than can the standard toxicity tests which are currently used. And because the biosensors are living organisms, they are accurate indicators of what is toxic to living creatures. Other toxicity tests, such as analytical chemical assays, do a good job of measuring levels of toxic agents in water samples, but they can't really tell scientists when there is enough of a toxin in the water to start damaging living cells.

The numerous dead fish lining the polluted shores of Lake Ontario indicate why this might be a particularly valuable characteristic of the biosensors. If government officials had had conclusive evidence earlier on that the industrial wastes spewed into the lake harmed aquatic life forms, the damage might have been contained.

Thanks to his success in obtaining grant money from various sources, DuBow supports a fairly large research team of 15--a lab technician, graduate students and undergraduate research interns.

"That's been the size of my team for a while now--I like to keep it at that level. I've been blessed with terrific students and I try as much as I can to be a role model. Their enthusiasm is infectious. That's a major reason why I work at a university and not a private research institute."

Theadmiration is mutual, although students in his lab confess to occasional grumbling over DuBow's other commitments--being a departmental chair takes its toll on his availability for research. But they acknowledge that the same skills which earned him a Leo Yaffe Award for outstanding teaching make him a terrific tutor when he is in the lab.

"When you can find him, within a mere five minutes, he can be extremely helpful," says one student on the research team. Adds another, "You can't avoid sharing his dedication."

DuBow isn't advocating that biosensors replace other methods for tracking pollution levels, but he does think that by adding biosensors to the existing arsenal, scientists might get a better sense of the types of toxins they're combating.

"Hopefully, (the biosensors) will be used in conjunction with other toxicity tests to quickly prioritize hazardous sites." The biosensors' commercial possibilities are currently being appraised by McGill's Office of Technology Transfer.

In a recent journal article, DuBow mused that the science surrounding the biosensors might be applied more broadly to humans one day.

"Ultimately, the information deciphered from this (project) may be used to assess which individuals are at greater or lesser risk when exposed to toxic agents because they lack (or contain) specific cellular defence mechanisms." Genetic tests might be used to alert individuals of their particular sensitivity to certain toxins.

DuBow's team has already done some research in this area. "We've been working on a small scale so far. This type of work is tougher to do since human genetics are far more complex."

What if genetic tests could successfully detect an individual's vulnerability to a certain form of pollutant--to motorcycle exhaust fumes, for instance? What would DuBow--a motorcycle enthusiast for over 20 years and the proud owner of a bright red Harley-Davidson--do if he was told that the exhaust fumes could make him seriously ill?

"My initial response would be, 'What part of the fumes cause the problems and can I eliminate it from the fumes?' Could I take some form of medication to eliminate the toxic effects on my system? If I get sick, is there a cure? I would do whatever I had to do to keep riding Harleys."

Darryl Gebien, a master's student in the Department of Pathology, is a science writing intern for the Reporter.