Wine drinking, creosote - eating fungus from the Eastern Cape
Dr Winston Leukes
Bioprospecting is a bit like mining for gold. It requires a good idea of where
to go searching, patience and a dose of good luck, but with bioprospecting the
ultimate prize is perhaps more valuable than gold.
The search for new organisms with previously unknown or more industrially
useful biological molecules, is one of the most important research areas for the
establishment of southern Africa's bio-economy. It is a high risk, high
potential reward activity where the probability of finding novel, valuable
biological compounds increases with the total biodiversity of the region. In the
rapidly approaching biotechnology age, a country's natural resources might
become just as valuable as its mineral resources for the promotion of economic
growth. South African biotechnologist Dr Winston Leukes shares one of his team's
bioprospecting successes with the discovery of a unique enzyme with excellent
industrial resources from a unique African fungus.
Enzymes
In nature, enzymes are natural catalysts which speed up or facilitate
specific reactions and many of them have some very valuable applications in
industry. Take for example the protease enzyme which naturally breaks down
protein molecules to simpler amino acids. Proteases are now used industrially in
washing powders to help remove protein stains. Your stone-washed denims?
Cellulose enzymes are valuable in the clothing industry. But for many of these
industrial applications, selecting the right cellulose or protease enzyme that
can operate under certain conditions - for example the hot cycle on your washing
machine or under acidic conditions, is the real secret to success.
The industrial enzyme market, valued at $2 billion per annum, with an annual
growth rate of 3 to 5%, has an increasing demand for differentiated products
with improved properties. Properties such as stability, activity at high
temperature (thermostability), wide substrate ranges, greater reaction speed and
wider pH range are often at the top of that list of properties. Leukes and team
discovered a laccase enzyme with all of the above properties in South Africa.
Laccase is an enzyme with considerable appeal. Its applications include the
detoxification of industrial effluent mostly from the paper and pulp and
petrochemical industries, use as a tool for medical diagnostics, and use as a
bioremediation agent to clean up herbicides, pesticides and certain explosives
in soil. It is also used as a cleaning agent for certain water purification
systems, as a catalyst for the manufacture of anti-cancer drugs, and even as an
ingredient in cosmetics.
Good luck
The fungus, tentatively known as UD4, was discovered during a bioprospecting
field trip by a group of biotechnologists from Rhodes University in South
Africa. Initially the team were headed towards the cold rain forests of Hogsback
to look for mushroom fungi, but due to car trouble half way there, they
abandoned their plan of driving up into the mountains, stopping instead where
they were and hiking through the semi-arid bush.
The fungus drew immediate attention from the researchers since it was growing
on wood treated with creosote, which is a strong protective agent against the
colonisation of wood by fungi. Furthermore, it was growing in direct sunlight,
which was also unusual since fungi normally prefer cool, wet environments. It
was assumed that the fungus must have some unique properties to survive that
harsh environment. This was found to be true when a unique laccase was isolated
from the fungus back in the laboratory.
Novelty
The novelty of the South African laccase lies mainly with its thermostability,
since it has an optimum operating temperature of 70°C in comparison to 55°C
for laccase from other sources. Also, it retains most of its activity at high
temperatures after long operating periods, which is favourable for industrial
processes since reactions take place faster at higher temperatures.
The characterization of the new laccase became the focus of a PhD project by
Mr Justin Jordaan at Rhodes University, who discovered two further exceptionally
beneficial properties of the thermostable laccase over other sources of the
enzyme. The thermostable laccase is extremely efficient at converting compounds
that it recognizes (substrates) and has a wider substrate range than other
studied laccases. The benefit of this in terms of application is that the enzyme
will act on a wider range of toxic compounds than other laccases and that
smaller quantities of the enzyme will be required to perform the same function,
thereby increasing the applicability of the enzyme by reduction of its cost.
The enzyme is currently being evaluated for the decolourisation of wine
distillery waste. The work is undertaken for the Water Research Commission of
South Africa by Oenozyme (an environmental biotechnology company) and Rhodes
University. Other applications of the enzyme are being developed by Oenozyme (a
start-up company emanating from research at Rhodes).
The novelty of this fungus was not limited to the production of the
thermostable laccase. It was found from DNA sequence analysis that its closest
relatives (other mushroom fungi) are far simpler in structure than UD4. The
results show that this fungus is uniquely African and is the first fungus of its
kind to be isolated internationally, a testament to the fungal biodiversity of
South Africa.
More information:
For further information contact Winston Leukes at w.leukes@ru.ac.za.
Public understanding of Biotechnology website www.pub.ac.za
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