VOA标准英语2015--Rock-Consuming Organisms Alter Views of Life Processes

 

Rock-Consuming Organisms Alter Views of Life Processes

LOS ANGELES—

Kenneth Nealson can be described in many ways, including "expert in microbiology and biochemistry."  But that's not the one he is most proud of.

"People call me the 'father of Shewanella,' " said Nealson, a professor of Earth sciences and biological sciences at the University of Southern California in Los Angeles.

Shewanella is an unusual bacterium¹ that shocked the scientific community. Nealson discovered it 25 years ago in a lake. Like other organisms, it breathes oxygen, but it also breathes rock.

Nealson displayed the phenomenon in a time-lapse video that shows Shewanella making a piece of manganese oxide² slowly disappear.

"That particle that you saw disappear before your eyes in 18 hours, under those conditions, should have been stable for thousands of years," he said.

All living things, including people, make energy through what’s called electron transfer. It involves taking electrons from the food we eat.

"When we breathe in oxygen, we give electrons to it, and it’s that voltage that allows us to make energy," Nealson said.

This process usually happens internally. But for the Shewanella and other mineral-breathing organisms, the electron transfer happens outside the cell.

When the process was discovered, it seemed impossible to the scientific community.

"This was one of the most exciting times in my career — when you realize you have something that probably no one else has and that almost no one is going to believe," Nealson said.

Since then, microbiologists have found other organisms that breathe metal, and Nealson said they are finally making it into science textbooks.

Building on Nealson’s work, one researcher in his lab, Annette Rowe, just made another discovery: bacteria that eat rock in ocean sediments⁴ as an energy source and transfer electrons from outside the cell membrane⁵ into the cell.

"So you actually don’t have to internalize it to get energy from it," Rowe said.

Nealson said the discovery is "going to be as wacky" as the Shewanella finding, "because you could see from the reviews of this that some people just didn’t believe it."

These findings have implications that extend to outer space and how life might exist on a planet like Mars. Nealson said one of his former students is now building an instrument that will attach to the arm of a planetary rover and give scientists a special set of eyes on the 2020 Mars mission.

"If you picked up a nice fluorescent⁶ signal from a Mars rock or sediment³ or core if we drilled into it, and all of a sudden you saw a certain colors of fluorescence, you would say, 'Whoop⁷, stop the train, let’s get a sample of this,' and look at it in more detail."

Meanwhile, scientists are drilling into the lower parts of the Earth’s crust, several kilometers down, to see whether there are forms of life there, living in ways much different than what we know as life on the surface

1 bacterium   

n.(pl.)bacteria 细菌

参考例句：

• The bacterium possibly goes in the human body by the mouth.细菌可能通过口进入人体。
• A bacterium is identified as the cause for his duodenal ulcer.一种细菌被断定为造成他十二指肠溃疡的根源。

2 oxide   

n.氧化物

参考例句：

• Oxide is usually seen in our daily life.在我们的日常生活中氧化物很常见。
• How can you get rid of this oxide coating?你们该怎样除去这些氧化皮？

3 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

4 sediments   

沉淀物( sediment的名词复数 )； 沉积物

参考例句：

• When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后，体积的70-80％是水。
• Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。

5 membrane   

n.薄膜，膜皮，羊皮纸

参考例句：

• A vibrating membrane in the ear helps to convey sounds to the brain.耳膜的振动帮助声音传送到大脑。
• A plastic membrane serves as selective diffusion barrier.一层塑料薄膜起着选择性渗透屏障的作用。

6 fluorescent   

adj.荧光的，发出荧光的

参考例句：

• They observed the deflections of the particles by allowing them to fall on a fluorescent screen.他们让粒子落在荧光屏上以观察他们的偏移。
• This fluorescent lighting certainly gives the food a peculiar color.这萤光灯当然增添了食物特别的色彩。

7 whoop   

n.大叫，呐喊，喘息声；v.叫喊，喘息

参考例句：

• He gave a whoop of joy when he saw his new bicycle.他看到自己的新自行车时，高兴得叫了起来。
• Everybody is planning to whoop it up this weekend.大家都打算在这个周末好好欢闹一番。