Position Available: Indestructible Bugs To Eat Nuclear Waste
Eight years ago, scientists using a metal rod here to probe the radioactive depths of a nuclear-waste tank saw something that shocked them: a slimy, transparent substance growing on the end of the rod.
They took the specimen into a concrete-lined vault where technicians peered through a 3-foot-thick window and, using robot arms, smeared a bit of the specimen into a petri dish. Inside the dish they later found a colony of strange orange bacteria swimming around. The bacteria had adapted to 15 times the dose of radiation that it takes to kill a human being. They lived in what one scientific paper calls a "witches' brew" of toxic chemicals.
It was a step forward for the U.S. Department of Energy, which has been looking for a few good bugs -- in particular, members of an emerging family of microbes that scientists call "extremophiles." These microbes can survive in some of Earth's most inhospitable environments, withstanding enormous doses of radiation, thriving at temperatures above boiling, and mingling with toxic chemicals that would kill almost anything else.
That makes them a potentially valuable tool in the Energy Department's effort to clean up vast amounts of nuclear waste, including the Savannah River Site near Augusta, Ga., and the Hanford Site near Richland, Wash. The department says it could cost as much as $260 billion to clean up its messes with conventional methods, which rely heavily on chemical treatment and robots. Using extremophiles could slash that bill.
Extremophiles eliminate toxins by ingesting them and breaking them down into relatively harmless components. The microbes also can reduce the hazard of radioactive wastes by changing them into insoluble forms that are much less likely to leak into aquifers and streams.
K. radiotolerans, seen through an electron microscope. At left, a colony of the bugs; at right, a single bacterium.
Outgoing Energy Secretary Spencer Abraham predicted this year that "in the not-too-distant future," extremophiles will be cleaning up nuclear waste and munching the pollutants of coal-fired power plants, including carbon dioxide, one of the causes of global warming. The National Aeronautics and Space Administration thinks if it can understand the mechanism that the bugs use to survive radiation, it might be able to use it to protect space crews against radiation on long voyages. The National Institutes of Health hopes the microbes' peculiar powers might help cancer patients survive more-intensive radiation therapy.
So far, scientists say that the extremophiles they have found in nature aren't harmful to humans. Laboratory-engineered modifications of these bugs, however, are likely to cause some controversy because no one knows what their long-term effects might be.
The berry-shaped bug discovered at the Savannah River Site was christened Kineococcus radiotolerans. Scientists have probed 95% of its genetic structure. They know what it does and what it eats -- it loves malt sugar -- but after 50 years of studying these sorts of bugs, they have no idea how they survive. Radiation shatters the genetic structures of living things, but extremophiles snap themselves back together in a matter of hours.
Christopher Bagwell , a microbiologist here, says Kineococcus has shown the ability to break down herbicides, industrial solvents, chlorinated compounds and other toxics, all while growing in a radioactive environment that shrivels other living things and turns glass brown.
Scientists know of at least a dozen extremophiles. The first was discovered in 1956 in Corvallis, Ore. Scientists were zapping cans of horse meat with high radiation, trying to establish the preservative value of food irradiation. One can developed an ominous bulge. Inside, the scientists isolated pink bacteria they had never seen before.
They gave it the scientific name Deinococcus radiodurans. But researchers were so amazed by the bug's resilience that some years later, they nicknamed it "Conan the Bacterium," spawning a folklore and debate among scientists that continues today. Because the microbes endure radiation at levels higher than any natural source, some scientists have argued that they must have ridden in on comets. Others speculate that they were the Earth's first residents after the planet was born in a radioactive explosion.
"Because of the amazing abilities of these organisms, they sort of bring out the poet in people," says John R. Battista, a microbiologist at Louisiana State University. He says speculation about outer space origins is like engaging in "mythology."
Extremophiles have recently been found on barren mountain tops and in the frozen plains of Antarctica, Dr. Battista says. He believes they are simply harmless, opportunistic creatures that have found a way to survive in conditions of severe drought, which, he says, damages cells in much the way radiation does. "It just waits until it gets dried out and then it gets blown somewhere else."
The original Conan proved to be a wimp among extremophiles. It could handle radiation, but not the solvent toluene and other chemicals normally found in bomb makers' wastes. So, in 1997, the Energy Department started work on a genetically manipulated bug that researchers called Super Conan.
Super Conan now lives in a petri dish at the Uniformed Services University of the Health Sciences, a U.S. military research facility in Bethesda, Md. It can handle nasty chemicals as well as radiation, but the researcher who developed it, Michael J. Daly, says the government is afraid to let it out.
"We're at a point where we could do some field trials," he says, adding that his sponsors at the Energy Department doubt the public is ready for the release of this laboratory-engineered bug into the environment. It might eat nuclear wastes, but they worry about what else might it do, he says.
Rather than confront such touchy matters, the department is confident it can find Super Conan's equivalent in nature, says Ari Patrinos, the department's director of biological and environmental research. He estimates that fewer than 1% of the Earth's bacteria forms have been identified: "There are plenty out there for our needs. We just have to pick and choose."
That's where Kineococcus comes in. The Savannah River Site, slapped together in the early 1950s to keep the U.S. ahead of the Soviet Union in the race to produce hydrogen bombs, has 49 underground storage tanks containing 35 million gallons of radioactive waste. The Energy Department has a much bigger mess at the Hanford site, a World War II weapons plant where leaking tanks have contaminated 80 square miles of groundwater with radiation and toxic chemicals.
Because the new orange bug made its home in nuclear wastes, no one can argue that putting it back there would be unnatural, say the scientists here. They believe they can grow kineococcus in petri dishes and then inject it into tanks and underground plumes of leaking wastes.
But Dr. Bagwell thinks it will take five more years of peering into the bug's genes before attempting such experiments. Twenty percent of the microbe's genetic structure, he says, involves "unknown functions."
无敌细菌与核共舞
八年前，当科学家们在美国萨瓦纳河畔(Savannah River)用金属棒探测一个核废料仓库的放射程度时，眼前的现象令他们惊呆了：一种粘著而透明的物质在金属棒的末端闪闪发光。
他们把采集来的样品放入一个用水泥密封的地窖里，技术人员只能通过一个3英尺厚的玻璃窗来探视里面的情形。然后，科学家们利用机器人把少量样品涂抹在佩氏培养皿中，结果发现里面长出了一种奇特的四处游动的橙黄色菌落。这种细菌能承受的放射剂量是人类所能承受的15倍，生活在被科学界戏称为“巫婆的杰作”的有毒环境下。
对于美国能源部来说这是一项突破，他们一直在寻觅一些能为环保作贡献的生物，特别是被科学家们称为“嗜极细菌”的一种逐步为人所知的微生物。这类细菌能在地球上一些人类无法居住的环境下存活，它们能忍受惊人的辐射，在沸点以上茁壮成长，并与那些足以杀死其他任何物质的有毒化学物质相融合。
上述特性使它们有望在美国能源部清除大量核废料的行动中发挥宝贵作用，除了乔治亚州萨瓦纳河畔外，华盛顿州汉福德(Hanford)也存放了许多核废料。能源部表示，若采用化学手段和机器人处理的传统方法，清除费用将高达2,600亿美元，而利用嗜极细菌能大大降低成本。
嗜极细菌主要通过吸收有毒物质，并分解成相对无害的成份来消灭它们。这些细菌还能把具有放射性的废料变成无法溶解的物质，从而减轻对地面蓄水层及河流的渗透，降低它们的危害性。
平易近人的能源部长斯宾赛?亚伯拉罕(Spencer Abraham)今年预计，“在不久的将来”，嗜极细菌将参与清除核废料以及二氧化碳等火电厂污染物的行动。二氧化碳增多是全球气候变暖的主要原因之一。美国国家航空航天局(The National Aeronautics and Space Administration)认为，如果自己能掌握嗜极细菌抗辐射的机制，它也许能更好地保护宇航员在长途飞行中免受辐射的侵害。美国国立卫生研究院(The National Institutes of Health)则希望嗜极细菌的独特威力能帮助癌症患者适应辐射剂量较高的化学疗法。
科学家们表示，迄今为止，他们发现的嗜极细菌对人类并无危害。不过实验结果表明这些细菌有可能引发争议，因为没人知道它们的长期效果如何。
这种在萨瓦纳河畔发现的浆果形微生物被命名为Kineococcus抗辐射细菌，科学家们已破解了其95%的基因结构。他们知道这些细菌喜欢吃麦芽糖，但在对此类生物研究了50年后，它们的生存之道依然是个谜。放射性物质破坏了其他生物的基因结构，但嗜极细菌却能在几小时之内把它们彻底消化。
微生物学家克里斯托弗?鲍威尔(Christopher Bagwell)指出，Kineococcus能分解除草剂、工业溶剂、氯化化合物以及其他有害物质，在扼杀其他生物的放射性环境下茁壮成长。
目前，科学家们至少了解十几种嗜极细菌，最早是1956年在俄勒冈州的Corvallis发现的。当时，科学家们利用大量辐射来处理马肉罐头，试图让辐射成为保存食物的防腐剂。突然，一个罐头膨胀起来，科学家们在里面发现了一种以前从未见过的粉红色细菌。
这种细菌的学名叫Deinococcus抗辐射细菌，但它的抵御能力实在令人震惊，几年后，研究人员给它起了个绰号叫“Conan”，科学家们至今依然对此争论不休。由于这种细菌的抗辐射程度超出了地球上了其他任何生物，一些科学家们认为它们来自彗星，而另一些人则猜测它们是地球上最早的生物，因为地球是经过了放射性爆炸而形成的。
路易斯安那州立大学(Louisiana State University)的微生物学家约翰?贝斯塔(John R. Battista)说：“由于这些细菌的能力惊人，它们不禁令人浮想联翩。”他表示，那些认为它们来自外层空间的推测简直是“神话”。
贝斯塔指出，嗜极细菌最近在光秃秃的山顶上和南极洲的冰原上被发现。他认为这些细菌是没有危害的生物，它们成功地在极端乾旱的条件下生存了下来。乾旱对生物细胞的破坏方式与辐射相似。
最早被发现的Conan被证明是嗜极细菌中的懦夫。它能对付辐射，但不能对付甲苯溶剂等通常在爆炸废料中发现的化学物质。因此，在1997年，美国能源部开始研究一种被成为超级Conan的基因变种细菌。
超级Conan目前存放在美国军方位于国马里兰州的研究机构Uniformed Services University of Health Sciences的佩氏培养皿中。这种细菌能消化有毒化学物质和辐射，但进行培育的研究人员迈克尔?戴利(Michael J. Daly)表示美国政府对它的实际运用感到担心。
“我们可以进行一些实验，”他说，但美国能源部担心公众对将这种实验室培育的细菌放在自然环境中抱有疑虑。这种细菌也许能消化核废料，但是否会消化别的东西呢？
美国能源部负责生物和环境研究的主任阿里?帕特里诺斯(Ari Patrinos)表示，尽管存在上述棘手问题，能源部依然相信能在自然界中找到超级Conan的对应物质。他估计，地球上被发现的细菌还不到总数的1%，因此“有许多细菌能满足我们的需求。我们则必须加以筛选。”
这时出现了Kineococcus抗辐射细菌。萨瓦纳河畔基地是上世纪50年代早期美国在与苏联争先研制氢弹的竞赛中建设而成的。当地拥有49个地下存储槽，存放了3,500万加仑的放射性废料。美国能源部在汉福德拥有一个容积大得多的存储点，那里有一个第二次世界大战的军工厂，存储槽泄露的有毒物质及辐射污染了方圆80平方英里的地下水源。
科学家们说，由于Kineococcus这种橙黄色细菌对核废料安之若素，没人会说把它们放在上述地点是莫名其妙的事。他们认为可以在佩氏培养皿中培育Kineococcus，然后把这些细菌放入存储槽和地下泄露点。
但鲍威尔认为，还需5年时间来了解这种细菌的基因结构，之后才能进行相关实验。他指出，其百分之二十的基因的功能尚不清楚。
