Bulletin

Issue: August 2005

Research in Action

A tale of two polysaccharides

If there's a case to be made for science imitating nature, it's scientists in labs who have to make it happen - watching, waiting, and tweaking to find out just how nature does it.

From left, front Dr Stanisich, Professor
Matthysse, PhD scholar Sanja Aracic,
and Professor Stone.

In the case of experiments under-way in La Trobe's microbiology department, it also involves a measure of nano-scale skullduggery - cloning synthetic genetic material and switching the synthetic bits with natural material excised from a string of bacterial DNA, to test their role.

It's all in a day's work for visiting US geneticist and IAS Distinguished Fellow Professor Ann Matthysse from the University of North Carolina, and her collaborators at La Trobe, Emeritus Professor in Biochemistry, Bruce Stone, and molecular biologist, Dr Vilma Stanisich, from the Department of Microbiology.

What is likely to happen, they know, is that the cells of the plant-colonising Agrobacterium will get very confused. Instead of directing the production of cellulose, a polysaccharide which helps the Agrobacterium bind to the roots of plants, they will probably send out a different set of instructions, resulting in the production of a different polysaccharide, called curdlan.

Studies at La Trobe have shown that both polysaccharides help the bacterium to survive in the soil, but why the Agrobacterium produces two so closely related substances is a biological mystery.

If the DNA switching trick works, the team will then reverse it, to see what happens when the cells are tricked into thinking they should produce cellulose; and if they do, science will be well en route to explaining how and why the organism synthesises both polysaccharides, when one might do.

Apart from a theoretical interest, why do we want to know? Because the results could help to improve agricultural disease control.

The likelihood is that plants all over the world cheerfully co-exist with these soil-dwelling bacteria, because they protect their hosts from disease.

Like 'good' bacteria in the human gut, they probably colonise the roots of plants to guard against pathogens invading the plant's 'digestive tract' where it is most vulnerable - using polysaccharides to bind and form a protective barrier over surfaces of the root system.

The hypotheses guiding these experiments might arguably never have happened independently of the collaboration between La Trobe and the University of North Carolina; they are the direct result of the scientific synchronicity that brought these scientists together.

Professor Matthysse and her colleagues at the University of North Carolina were investigating the synthesis of one polysaccharide, and Professor Stone and Dr Stanisich at La Trobe, the other. When the three researchers discovered two years ago they had been simultaneously investigating two separate if inextricably linked processes of the same organism, they quickly recognised the value in collaboration.

'The more we talked it over the more evident it was there were experiments we needed to do that none of us could tackle on our own, but all three of us could do together,' says Professor Matthysse.

'Almost nothing is known about why a particular protein synthesises one type of polysaccharide and a related protein synthesises another type.

'We've been looking at the synthesis of one polysaccharide, cellulose, and they've been looking at the synthesis of a closely related polysaccharide, curdlan. Nobody else has a system where they've got two proteins so closely related, made by the same organism, which synthesise different but related molecules.'

Because both teams have now invested more than a decade in separate research, they clearly have a few hunches about the likely outcomes from their integrated work, but Professor Matthysse says they're still 'prepared to be surprised.'

'Results so far indicate that the switching experiments will work.'

These results, she says, are interesting 'because if you want to make synthetic polysaccharides it helps to know how the bacterial cell does it.'

Customers of applied science may be interested too in their application for medical and industrial use - particularly the US Department of Energy, which is interested in the potential uses of cellulose as an alternative energy source. The Department funds Professor Matthysse's work in the US.