London, July 19 : American researchers have identified the bacterial genes that give rise to the smell of earth.
Brown University experts David Cane and Chieh-Mieh Wang say that the smell of earth comes from a combination of two harmless chemicals called geosmin and methylisoborneol.
They say that both chemicals belong to a class of compounds called terpenes, and are synthesised by soil bacteria.
Cane identified the gene that helps make geosmin last year, but methylisoborneol remained elusive.
In their latest study, the researchers scanned a database containing all 8000 genes from a soil bacterium called Streptomyces, and came across one that looked like it coded for a terpene catalyst. However, when the researchers inserted the gene into another bacterium, no tarpenes were found.
"We then noticed another gene, right next to the first one, which looked like it might code for a catalyst that adds a single carbon to chemical compounds," New Scientist magazine quoted Cane as saying.
The researchers realised that, together, the two genes could produce the elusive methylisoberneol.
When they genetically engineered an E. coli bacterium to express both genes, they obtained the scented compound.
Cane points out that methylisoborneol is also responsible for the muddy smell that tap water sometimes takes on when reservoirs are invaded by blooms of blue-green algae.
He thinks that algae probably also have both genes.
The researcher believes that knowing their sequence may help detect the early signs of blooming, and thereby save the millions of dollars that are often spent on treating full-blown blooms.
A report on the research appears in the Journal of the American Chemical Society.