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Nature News:“砷基生命”研究遭质疑 精选

已有 11906 次阅读 2010-12-8 07:54 |个人分类:憨人的科学|系统分类:博客资讯| 生命, 质疑, 砷基生命, 生命物质

 

 

      加拿大不列颠哥伦比亚大学微生物学家Rosemary Redfield率先对Felisa Wolfe-SimonScience文章中的实验细节提出质疑,但是发表在博客上。 加州拉霍亚Scripts研究所的生化学家Gerald Joyce也对此作出评论“这是一个关于生物适应环境的故事,而与外星人无关” (这个评论应该是针对NASA的新闻发布会和新闻媒体对研究结果的过度解读)。

     质疑的主要问题主要有两点:一是数据不够clear,所谓无磷培养条件还是有残留的痕量磷(5微摩,来源于实验材料,如其他盐类,这个难以克服),第二就是就是这篇文章还没有提供充分证据证明砷确实掺入到DNARNA中去。鉴于第一条是客观条件的限制,无法解决,因此核心问题就是第二个了。做回事后诸葛亮:这个问题俺当时也想过,也觉得这部分证据有点单薄,如何排除砷不是真正掺入了DNA而像溴化乙啶(一种DNA荧光染料)一样插入DNA的螺旋沟内,或者只是简单得附着在DNA上?作者做了CCT分析(Thermo X-series quadrupole ICP-MS with Collision Cell Technology,俺不懂这个实验,所以不能判断它的价值),但是对于这么个重大结论,证据是多多亦善,孤证往往是不够的(not good engough)。 为什么不能再多做一些呢?MIT的生化学家Roger Summon的建议是靶向质谱分析(把纯化的DNA打断,通过质谱测定精确的分子量,从分子量变化确定砷是否真的掺入)。

    批评者的结论:GFAJ-1代表新形式的“砷基生命”这一结论不够成熟。

       质疑是科学研究的正常过程,科学就是在质疑声中成长的,大家也不必大惊小怪。有点遗憾的是,Felisa Wolfe-Simon对质疑的问题没有做出直接回答,还表示不想介入争论,并说出匪夷所思的话“任何(质疑性)言论应该像我们的文章一样经过同行评议和审查过程...”(Any discourse will have to be peer-reviewed in the same manner as our paper was, and go through a vetting process so that all discussion is properly moderated." ) 科学的原则:谁主张,谁举证,质疑者有提问的权利,却没有提供证据的义务;只要提出的问题是合理的(reasonable),被质疑者都要面对---作者的答复却令人失望。

 

 

 

看来,对一些新的重大突破还是要多一些挑剔的眼光、谨慎的态度。

 

 

这里我提供了这篇论文的全文和补充数据的PDF文件, 感兴趣、又有专业基础的朋友可以去读原文。

 

 

http://www.nature.com/news/2010/101207/full/468741a.html

 

Published online 7 December 2010 | Nature | doi:10.1038/468741a

News

Microbe gets toxic response

Researchers question the science behind last week's revelation of arsenic-based life.

Alla Katsnelson

The cells’ large vacuoles may indicate that they are sequestering arsenic.Science/AAAS

Days after an announcement that a strain of bacteria can apparently use arsenic in place of phosphorous to build its DNA and other biomolecules — an ability unknown in any other organism — some scientists are questioning the finding and taking issue with how it was communicated to non-specialists.

Many readily agree that the bacterium, described last week in Science and dubbed GFAJ-1 (F. Wolfe-Simon et al. Science doi:10.1126/science.1197258; 2010), performs a remarkable feat by surviving high concentrations of arsenic in California's Mono Lake and in the laboratory. But data in the paper, they argue, suggest that it is just as likely that the microbe isn't using the arsenic, but instead is scavenging every possible phosphate molecule while fighting off arsenic toxicity. The claim at a NASA press briefing that the bacterium represents a new chemistry of life is at best premature, they say.

"It's a great story about adaptation, but it's not ET," says Gerald Joyce, a biochemist at the Scripps Research Institute in La Jolla, California.

At the press briefing, Steven Benner, a chemist at the Foundation for Applied Molecular Evolution in Gainesville, Florida, who was invited to the event to offer outside comment, used the analogy of a steel chain with a tinfoil link to illustrate that the arsenate ion said to replace phosphate in the bacterium's DNA forms bonds that are orders of magnitude less stable. Not only would the organism's DNA have to stay together in spite of the weaker bonds, says Benner, but so would all the molecules required to draw arsenate from the environment and build it into the genetic material. Co-authors of the paper, including Paul Davies, an astrobiologist at Arizona State University in Tempe, have countered that the arsenate bonds could be reinforced by specialized molecules, or that arsenic-based life simply has a higher turnover for molecular disintegration and assembly than does conventional life.

The big problem, however, is that the authors have shown that the organism takes up arsenic, but they "haven't unambiguously identified any arsenic-containing organic compounds", says Roger Summons, a biogeochemist at the Massachusetts Institute of Technology in Cambridge. "And it's not difficult to do," he adds, noting that the team could have directly confirmed or disproved the presence of arsenic in the DNA or RNA using targeted mass spectrometry.

Some researchers suggest that the authors' own data hint at an organism that is simply absorbing and isolating arsenate while making use of the trace phosphates in its environment. For one thing, says Joyce, the paper shows that the organisms appear bloated, and contain large, vacuole-like structures — often a sign of sequestered toxic material. The arsenate-grown cells were analysed in their resting phase, which requires less phosphate for survival than does active growth, notes Joyce, and cells grown in high concentrations of arsenate did not seem to contain any RNA — possibly because RNA production had shut down to conserve phosphate. One calculation in the paper showed that the DNA in arsenate-grown cells actually contained 26 times more phosphorus than arsenic.

"I fault the authors for not noticing these things and sorting them out," says Rosemary Redfield, a microbiologist at the University of British Columbia in Vancouver, Canada, whose summary of the paper's problems, posted on her blog on 4 December, has already had more than 30,000 hits. "We shouldn't have to do the thinking for them."

Felisa Wolfe-Simon, a NASA astrobiology research fellow at the US Geological Survey in Menlo Park, California, and the study's lead author, refused to address criticisms. "We are not going to engage in this sort of discussion," she wrote in an e-mail to Nature. "Any discourse will have to be peer-reviewed in the same manner as our paper was, and go through a vetting process so that all discussion is properly moderated."

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But Jonathan Eisen, a microbiologist at the University of California, Davis, calls this "ludicrous", after a NASA press release drew media attention with claims of an "astrobiology finding that will impact the search for evidence of extraterrestrial life", a theme that Wolfe-Simon echoed at the briefing. "It is absurd for them to say that they are only going have the discussion in the scientific literature, when they started it," he says.

Ginger Pinholster, a spokeswoman for Science 's publisher, the American Association for the Advancement of Science in Washington DC, noted that the journal regards significant responses to high-visibility articles, as well as efforts to replicate the work, as a "key goal of publication". Pinholster also pointed out that the journal's own press summary of the paper made no mention of the search for extraterrestrial life, nor did Science "organize any additional promotional events". 

延伸阅读: This Paper Should Not Have Been Published http://www.slate.com/id/2276919/pagenum/all/

 

 



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