Science - October 30, 2014

Battling it out with bananas in Boston

Text:
Rob Ramaker

A group of Wageningen students has devised a weapon against the
disease that is threatening banana plants worldwide. In Boston they will be competing against biotechnology students from across the world.

Every evening, just before 11 p.m., a siren wails through the chemistry building. Closing time. It is a sound that Wen Wu, a fifth-year Biotechnology student, has heard regularly in recent weeks. Here, with a team of fellow students, she has been tinkering relentlessly on a bacterium. The biotechnologists want to transform the organism into a weapon against Panama disease, a worldwide threat to banana plants.

They plan to submit their project to iGem, a student competition in the field of ‘synthetic’ biology. Starting 30 October, the Wageningen students will be competing in Boston against some 250 student teams from across the world. Synthetic biology is a discipline in which hereditary material is radically changed so that organisms do what we want them to do. In addition, the organization running iGem wants to improve the way this process is structured: entries must be constructed of ‘bricks’, Lego-like modules that can be combined in countless ways.



Panama disease

Wageningen team’s entry is called BananaGuard. It is designed to act as a bacterial weapon against the dreaded Panama disease, which is caused by the fungus Fusarium oxysporum. Worldwide, Panama disease forms one of the greatest threats to the cultivation of this fruit. In the 1950s the then dominant banana variety Gros Michel succumbed to Panama disease. Growers responded by switching to the resistant Cavendish variety. But since the 1990s this variety too has been under attack, from a new strain of Fusarium. The disease is jeopardizing not only the availability of one of the most popular fruits, but also the economic foundations of a number of impoverished developing countries. The weapon the Wageningen students are employing in BananaGuard is an adapted soil bacterium. This behaves normally until it notices Fusarium. Then the new system becomes active and the bacterium attacks the fungus. This is a complex project involving many parts. For instance, the bacterium must first succeed in finding the fungus. To enable this, the participants drew inspiration from soil bacteria with immunity to Fusarium. Evidently, these have a sensor that reacts to fusaric acid, a unique substance that the fungus secretes to help it penetrate plant roots.

Once the fungus has been noticed, the sensor switches on a couple of genes. These produce four types of fungus poison. Wu has shown that this approach does indeed halt Fusarium, in an experiment in which she cultivated fungi in a Petri dish, with and without the addition of BananaGuard. She is still awaiting the results of greenhouse tests in which the bacteria have been placed directly onto the roots of banana plants. 



I wanted to take part in iGem as soon as I heard about it. It is fun science to set up something yourself.


Genetic modification

In the greenhouse where Wu is carrying out her tests, it is clear why BananaGuard is more than an academic exercise. Visitors are allowed into these areas only if they are wearing a white coat and tall, disposable boots. Ranged here are banana plants, different species and varieties, large and small, all laid out in neat rows. It seems like a tranquil scene, but Fernando Garcia Bastida, a doctoral candidate with Biointeractions and Plant Health, disabuses visitors of that notion. A closer look reveals sallow leaves and silver stalks, some of which have burst open; signs that all these plants are contaminated with Fusarium and typically will soon die.

In the greenhouse Bastida, whose PhD supervisor is banana researcher Gert Kema, is testing related wild varieties for resistance. But even once he finds the genes responsible for the resistance, it will be difficult to get them into the species in need of protection. This is because banana trees reproduce by cloning rather than pollination. This rules out the use of conventional ‘cross breeding’ to acquire the desired characteristic. Alternatively, any change made in the lab falls within the scope of genetic modification, so it is debatable whether society would accept this kind of solution.

An advantage of BananaGuard, say the students, is that it doesn’t create any genetic changes in food crops. However, it is still going to be difficult to convince society that it is okay to release genetically modified bacteria into nature. To allay fear as much as possible, BananaGuard is being given two types of security. The first is a kill switch, which causes the bacterium to commit suicide after it has been active. Secondly, the further distribution of the bacterium’s anti-fungus genes is prevented by an emergency brake. As soon as BananaGuard tries to share its genes with another bacterium, it poisons both itself and the recipient.


Deadline

For students, participating in iGem is not like doing a regular internship or thesis, says supervisor Nico Claassens. They create their own idea rather than join an ongoing project. And they do their own preliminary research. In addition, the participants seek sponsors, organize public events and cooperate with researchers in other groups. It is precisely this broad responsibility, thinks Claassens, that attracts dedicated, ambitious students. Since June, seven students have been working full time in a practicals lab on the Dreijen campus. Many other students are providing supporting services. Most of the participants took no summer holiday this year and, with the deadline approaching, they are increasingly having to sacrifice their free evenings and weekends. ‘My social life has come to a complete standstill,’ says team captain Wu. But she doesn’t doubt for a moment that it is all worthwhile: ‘I wanted to take part in iGem as soon as I heard about it. It is fun science to set up something yourself.’

As the deadline of 18 October looms ever closer, the stress is palpable. They knew from the outset that their idea was too ambitious to be completed in full; completing the individual parts would be a great achievement in itself. They work through the last night until six o’clock in the morning in a student kitchen on the Haarweg. Then the Edit button disappears and their web page is locked down. In the end, they did manage to largely complete and describe their sensor, fungus poisons and kill switch. ‘It isn’t 100 percent,’ says Wu. ‘But we are pretty satisfied.’ In the weekend after the deadline she leafs quietly through the summary pages produced by the other teams. It makes her feel optimistic: ‘In our track, nutrition, we are among the top teams, but you can’t read all 250 pages.’ She is enthusiastic about finally going to Boston, but she’s also nervous. Now, at last, they will find out how they have done. ‘And I’d really like to win.’

More about Banana Guard: http://2014.igem.org/Team:Wageningen_URhave



Photo; Sven Menschel



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