英語聽力文摘 地球上最成功的物種

00:00

00:00

MP3下載 文本下載

https://online2.tingclass.net/lesson/shi0529/0007/7643/329.mp3

https://image.tingclass.net/statics/js/2012

地球上最成功的物種

For many scientists, a species’ success is measured by sheer numbers. In that case, the most successful species known to man is a type of bacterium known as S-A-R-11, or SAR-11 for short. Scientists estimate that there are two-hundred and forty times a billion billion billion SAR11 cells floating around in the oceans. Now that makes six-billion humans sound like a mere handful.

SAR11 bacteria are known for their ability to transform one substance into another, which is why they are such an important part of the Earth’s chemical cycles. Although scientists are still uncertain about SAR11′s specific role, it appears to produce carbon dioxide using the oxygen and carbon from organic matter that’s derived from photosynthesis. Scientists speculate that SAR11 plays a major role in the way the ocean’s surface acts as a giant carbon pump that removes carbon dioxide from the atmosphere.

The catch is that SAR11 is what is known as an uncultured organism, which means that scientists haven’t been able to cultivate it under laboratory conditions. This requires scientists to develop pretty indirect genetic methods just to be able to study SAR11 cultures. Now that this technology is available, scientists are sequencing the SAR11 genome in order to figure out exactly what kinds of carbon it uses, and why it’s so successful at ocean living.

對很多科學家來說，一個物種的成功完全取決于數(shù)量。如果是那樣是話，為人類所知的最成功的物種就是一種簡稱“SAR-11”的細菌。科學家們估計海洋中的SAR11細胞的數(shù)量超過2 x 10的28次方個。那讓60億人類聽起來屈指可數(shù)。

SAR11細菌以其轉換物質的能力為人所知。而這也使得它們成為地球化學循環(huán)中重要的部分。盡管科學家不能確定SAR11的具體作用。但它似乎可以使來自于光合作用的氧氣和有機物種的碳發(fā)生作用，產生二氧化碳。科學家推測SAR11在海洋表面扮演著重要的作用，作為一個巨大的碳泵移除空氣中的二氧化碳。

但目前SAR11是為培養(yǎng)生物，也就是說科學家不能在實驗室里培養(yǎng)出這種細菌。因此需要科學家們研制出間接遺傳方法，來研究SAR11。既然這項技術可用，科學家為了弄清楚究竟SAR11用的是哪種碳以及為什么它會如此的成功在海洋中生活，正在排序它的基因組。