TED日本語 - 二人の若き科学者、バクテリアでプラスチックを分解

Miranda Wang: We're here to talk about accidents. How do you feel about accidents? When we think about accidents, we usually consider them to be harmful, unfortunate or even dangerous, and they certainly can be. But are they always that bad? The discovery that had led to penicillin, for example, is one of the most fortunate accidents of all time. Without biologist Alexander Fleming's moldy accident, caused by a neglected workstation, we wouldn't be able to fight off so many bacterial infections.

Jeanny Yao: Miranda and I are here today because we'd like to share how our accidents have led to discoveries. In 2011, we visited the Vancouver Waste Transfer Station and saw an enormous pit of plastic waste. We realized that when plastics get to the dump, it's difficult to sort them because they have similar densities, and when they're mixed with organic matter and construction debris, it's truly impossible to pick them out and environmentally eliminate them.

MW: However, plastics are useful because they're durable, flexible, and can be easily molded into so many useful shapes. The downside of this convenience is that there's a high cost to this. Plastics cause serious problems, such as the destruction of ecosystems, the pollution of natural resources, and the reduction of available land space. This picture you see here is the Great Pacific Gyre. When you think about plastic pollution and the marine environment, we think about the Great Pacific Gyre, which is supposed to be a floating island of plastic waste. But that's no longer an accurate depiction of plastic pollution in the marine environment. Right now, the ocean is actually a soup of plastic debris, and there's nowhere you can go in the ocean where you wouldn't be able to find plastic particles.

JY: In a plastic-dependent society, cutting down production is a good goal, but it's not enough. And what about the waste that's already been produced? Plastics take hundreds to thousands of years to biodegrade. So we thought, you know what? Instead of waiting for that garbage to sit there and pile up, let's find a way to break them down with bacteria. Sounds cool, right?

Audience: Yeah. JY: Thank you. But we had a problem. You see, plastics have very complex structures and are difficult to biodegrade. Anyhow, we were curious and hopeful and still wanted to give it a go.

MW: With this idea in mind, Jeanny and I read through some hundreds of scientific articles on the Internet, and we drafted a research proposal in the beginning of our grade 12 year. We aimed to find bacteria from our local Fraser River that can degrade a harmful plasticizer called phthalates. Phthalates are additives used in everyday plastic products to increase their flexibility, durability and transparency. Although they're part of the plastic, they're not covalently bonded to the plastic backbone. As a result, they easily escape into our environment. Not only do phthalates pollute our environment, but they also pollute our bodies. To make the matter worse, phthalates are found in products to which we have a high exposure, such as babies' toys, beverage containers, cosmetics, and even food wraps. Phthalates are horrible because they're so easily taken into our bodies. They can be absorbed by skin contact, ingested, and inhaled.

JY: Every year, at least 470 million pounds of phthalates contaminate our air, water and soil. The Environmental Protection Agency even classified this group as a top-priority pollutant because it's been shown to cause cancer and birth defects by acting as a hormone disruptor. We read that each year, the Vancouver municipal government monitors phthalate concentration levels in rivers to assess their safety. So we figured, if there are places along our Fraser River that are contaminated with phthalates, and if there are bacteria that are able to live in these areas, then perhaps, perhaps these bacteria could have evolved to break down phthalates.

MW: So we presented this good idea to Dr. Lindsay Eltis at the University of British Columbia, and surprisingly, he actually took us into his lab and asked his graduate students Adam and James to help us. Little did we know at that time that a trip to the dump and some research on the Internet and plucking up the courage to act upon inspiration would take us on a life-changing journey of accidents and discoveries.

JY: The first step in our project was to collect soil samples from three different sites along the Fraser River. Out of thousands of bacteria, we wanted to find ones that could break down phthalates, so we enriched our cultures with phthalates as the only carbon source. This implied that, if anything grew in our cultures, then they must be able to live off of phthalates. Everything went well from there, and we became amazing scientists. (Laughter)

MW: Um ... uh, Jeanny. JY: I'm just joking.

MW: Okay. Well, it was partially my fault. You see, I accidentally cracked the flask that had contained our third enrichment culture, and as a result, we had to wipe down the incubator room with bleach and ethanol twice. And this is only one of the examples of the many accidents that happened during our experimentation. But this mistake turned out to be rather serendipitous. We noticed that the unharmed cultures came from places of opposite contamination levels, so this mistake actually led us to think that perhaps we can compare the different degradative potentials of bacteria from sites of opposite contamination levels.

JY: Now that we grew the bacteria, we wanted to isolate strains by streaking onto mediate plates, because we thought that would be less accident-prone, but we were wrong again. We poked holes in our agar while streaking and contaminated some samples and funghi. As a result, we had to streak and restreak several times. Then we monitored phthalate utilization and bacterial growth, and found that they shared an inverse correlation, so as bacterial populations increased, phthalate concentrations decreased. This means that our bacteria were actually living off of phthalates.

MW: So now that we found bacteria that could break down phthalates, we wondered what these bacteria were. So Jeanny and I took three of our most efficient strains and then performed gene amplification sequencing on them and matched our data with an online comprehensive database. We were happy to see that, although our three strains had been previously identified bacteria,two of them were not previously associated with phthalate degradation, so this was actually a novel discovery.

JY: To better understand how this biodegradation works, we wanted to verify the catabolic pathways of our three strains. To do this, we extracted enzymes from our bacteria and reacted with an intermediate of phthalic acid.

MW: We monitored this experiment with spectrophotometry and obtained this beautiful graph. This graph shows that our bacteria really do have a genetic pathway to biodegrade phthalates. Our bacteria can transform phthalates, which is a harmful toxin, into end products such as carbon dioxide, water and alcohol.

I know some of you in the crowd are thinking, well, carbon dioxide is horrible, it's a greenhouse gas. But if our bacteria did not evolve to break down phthalates, they would have used some other kind of carbon source, and aerobic respiration would have led it to have end products such as carbon dioxide anyway.

We were also interested to see that, although we've obtained greater diversity of bacteria biodegraders from the bird habitat site, we obtained the most efficient degraders from the landfill site. So this fully shows that nature evolves through natural selection.

JY: So Miranda and I shared this research at the Sanofi BioGENEius Challenge competition and were recognized with the greatest commercialization potential. Although we're not the first ones to find bacteria that can break down phthalates, we were the first ones to look into our local river and find a possible solution to a local problem. We have not only shown that bacteria can be the solution to plastic pollution, but also that being open to uncertain outcomes and taking risks create opportunities for unexpected discoveries.

Throughout this journey, we have also discovered our passion for science, and are currently continuing research on other fossil fuel chemicals in university. We hope that in the near future, we'll be able to create model organisms that can break down not only phthalates but a wide variety of different contaminants. We can apply this to wastewater treatment plants to clean up our rivers and other natural resources. And perhaps one day we'll be able to tackle the problem of solid plastic waste.

MW: I think our journey has truly transformed our view of microorganisms, and Jeanny and I have shown that even mistakes can lead to discoveries. Einstein once said, "You can't solve problems by using the same kind of thinking you used when you created them." If we're making plastic synthetically, then we think the solution would be to break them down biochemically.

Thank you. JY: Thank you.

(Applause)