Scientists at the John Innes Centre (JIC), Norwich(1) have discovered the gene that gives freshly turned soil its distinctive smell. A smell, it is believed, that enables camels to find water in the desert. The ‘earthy’ smell is caused by geosmin(2), a chemical produced by a common bacterium, Streptomyces coelicolor(3), that is found in most soils. The discovery of the gene that produces geosmin is reported in the International science journal the Proceedings of the National Academy of Sciences of the USA.
“The smell of Streptomyces may be a matter of life and death to the camel” said Professor Keith Chater (Head of Molecular Microbiology at JIC), “but these bacteria are also of enormous importance to humans as they are a major source of the antibiotics we use in medicine. This discovery was made using a technique that will allow us to better understand how Streptomyces makes the chemicals that are so important to us.”
The JIC researchers tracked down the source of Streptomyces’ smell to one gene out of the 8,000 that make up its complete genome(4). The Norwich scientists have been studying Streptomyces for years because of its importance as a natural chemical factory that makes a large number of useful medicines, it produces anti-cancer agents and immuno-suppressants as well as antibiotics. A year ago the JIC team, working with colleagues at the Sanger Centre near Cambridge, announced they had completely sequenced all 8,000 genes of Streptomyces. Their next challenge was to sort out what each of these 8,000 genes did. Fortunately, they had just invented a method to selectively switch off individual genes and so they began to use this to study the genes of Streptomyces. Among the 8,000 genes were a couple that the scientists thought might be responsible for making geosmin, so they tried switching them off to see what happened. Sure enough, switching off one of the genes eliminated the smell, and when they checked they found that the bacteria no longer made geosmin.
“Our discovery may seem a bit trivial but it demonstrates that we can now unravel how all the genes in this important bacteria work ” said Professor Chater . He concluded, “The discovery is not as useless as it first seems. Gardeners may delight in the smell of geosmin in freshly turned soil but the smell is less welcome when it is produced by pharmaceutical factories that are growing Streptomyces to produce antibiotics. By shutting down the bacteria’s ability to produce geosmin we can make the factories less smelly neighbours.”
Pictures of Streptomyces coelicolor are available at: http://www.jic.bbsrc.ac.uk/corporate/Media-and-Public/press-page.htm
John Innes Centre. February 2003.