英语听力文摘 English Digest 428、泥土的芬芳（在线收听）

The Smell of Dirt

A lot of people love that fresh-dirt smell. The surprising thing, though, is that it isn’t coming from the dirt itself. Microbiologists have traced the pleasant odor to an organic chemical called “ geosmin“.”

No way! But how does geosmin get into dirt?

A microbial geneticist named Keith Chater at the John Innes Center in England has traced geosmin down to a common bacterium called Streptomyces coelicolor. He even found out exactly which gene in the little critters causes them to produce geosmin.

No way! A bacterium is producing the chemical that smells so good?

Interestingly enough, there are unconfirmed reports that animals are attracted to fresh dirt in the desert, and go there looking for water. As they nose around the dirt, they pick up plenty of S. coelicolor, which then hitch a ride from one oasis to the next.

If it’s true, then the bacteria in general may create the odor in order to attract animals. The animals find water, the bacteria are spread, and everyone is happy.

不少人喜欢闻新鲜泥土的芬芳，出人意料的是芬芳不是来自泥土本身，微生物学家寻根溯源，发现宜人的香味是来自有机化学物：土臭素。

这不可能！土臭素怎么钻进泥土的呢？

Keith Chater 是英国John Innes中心的一名微生物遗传学者，他发现一种常见的叫蓝色链霉菌的细菌可以分泌土臭素。他甚至还能确定蓝色链霉菌中哪种基因产生土臭素。

没可能啊！细菌能分泌好闻的化学物质？

有趣的还不止这个，有报道还称沙漠动物就是靠新鲜泥土的芬芳寻找水源，不过有待考证。动物们找寻绿洲的同时，成为大量蓝色链霉菌的媒介，搭载蓝色链霉菌游曳绿洲间。

如果蓝色链霉菌普遍散发香气吸引动物，动物寻找到水源；而蓝色链霉菌也能因此繁衍，这不是双赢吗？
 

 geosmin：土臭素

Streptomyces coelicolor：蓝色链霉菌