Thursday, December 02, 2010
ARSENIC AND OLD ... (OR NEW) ... BACTERIA
Life is mostly composed of the elements Carbon, Hydrogen, Nitrogen, Oxygen, Sulfur, and Phosphorus. And these are all generally taken to be essential to life. Phosphorus contributes to the backbone of the DNA double helix, and to energy related molecules, among its many functions. Arsenic is chemically similar to Phosphorus but heavier, and somewhat different in the strength of its chemical bonds. Most living things, when Arsenic is available may substitute Arsenic for Phosphorus in some of their body's molecules, but then their body's chemical reactions go awry and the organism dies.
Felisa Wolfe-Simon (a scientist working with the NASA Astrobiology Institute, and the U.S. Geological Survey, Menlo Park, CA) and her co-workers have isolated or created a bacterium that is able to substitute Arsenic for Phosphorus and survive in an environment that is very rich in Arsenic and very weak in Phosphorus. (or pure Arsenic?)
The existence of life with chemistry significantly different from all other forms of life previously known obviously expands the possibilities for finding new life forms on Earth, and also in extra-terrestrial environments. It per-force widens the field of search.
There are many obvious questions. For example:
1 - Does this bacterium in its natural habitat substitute Arsenic for Phosphorus, or is the presence of Arsenic in its body an artifact or creation of the isolation process? In other words is this an old bacterium with Arsenic or a new form of life created in the Petri dish and the test tube?
1a - Does the bacterium directly from the pond survive in a pure Arsenic environment? Does the isolated bacterium survive in a pure Arsenic environment?
2 - Recent investigations have suggested there is a single ancestor for all life on earth (http://www.sciencenews.org/view/generic/id/59133/title/All_present-day_life_arose_from_a_single_ancestor). Is this result a refutation of that study? Or is this bacterium a descendent of that ancestor that has developed special powers? Or (again) is this a new life form?
3 - Results announced at highly hyped news conferences and on the front page of major newspapers have a depressing history of turning out to be not quite right. Will this Arsenic endowed bacterium result survive the inevitable massive effort to extend or disprove it?
(Note 12/5/2010 -- Here's one example of a skeptical post with a critique of the way the results are stated and checked. It's not a refutation, but a call for more tests and clearer descriptions - http://rrresearch.blogspot.com/2010/12/arsenic-associated-bacteria-nasas.html. Science works properly when results are obtained, described, and explained, and then the results are tested to obtain new, more complete results, and then these are described and explained.)
4 - If Arsenic can be substituted for Phosphorus in a living organism, can other substitutions be possible? Obviously Silicon for Carbon would be of great interest. (If the "organ" in "organic" stands for Carbon, then would a Silicon based life form be a "silicism"?) Also, Sulphur for Oxygen! (Some environments on Earth - and Venus - for example, are rich in hostile Sulphuric compounds.)
5 – After some confusion, the Press Conference seemed clear that this bacterium uses both Arsenic and Phosphorus. The substitution is not complete. Thus, would it be correct to say that, at least so far, it remains true that elements Carbon, Hydrogen, Nitrogen, Oxygen, Sulfur, and Phosphorus are ALL necessary for life?
One major result that is still lacking is the X-Ray diffraction confirmation of the Arsenic imbued DNA. (Note... X-Ray diffraction studies by Rosalind Franklin of normal DNA was just recently the subject of PHOTOGRAPH 51, by Anna Ziegler, an EST / SLOAN theatrical production at the Ensemble Studio Theatre.)
There is no "SCIENCE of Unintended Consequences," just random warnings about the possible hazards of particular developments from some people, and vague assurances about their safety from others. The possibility of an entire new branch of biochemistry (essentially alien to all previously understood biochemistry) suggested by the video news conference about this result, should be one good reason for a scientific process of dealing with the ramifications of new technology.
(The possibility of alien chemistry life forms might permit one horror-story alien possibility: A strange life-form in space that senses electromagnetic radiations from a planet (eg Radio & TV radiating out into space) and then homes in on the planet to consume it).
Felisa Wolfe-Simon is attractive, enthusiastic, well-spoken, knowledgeable and bright. She is (and this can be bad or good, media-wise -- and irrelevant scientifically) cutesy, with a sly smile, somewhat egotistical (with a tendency to say "I" when "we" would be better, and to reference great scientific milestones), argumentative, and somewhat scientifically not-quite-clear-and-accurate when not speaking technically.
She came to the Press Conference well prepared, with clear visual back-up material. As a media personality and scientific spokesperson and advocate, Felisa may have a very bright future. (Video of the whole Press Conference is embedded below.)
The paper is published in SCIENCE, the journal of the AAAS. Unfortunately, the paper, while online, is not free, and requires either membership in the AAAS ($99 & up depending on your stage of life) or a fee for 24 hour use of the one paper on one computer. (Or wait a week or two for the December 2, 2010 SCIENCE magazine to reach your library.)
Felisa had speculated earlier on the possibility of finding Arsenic tolerant bacteria. (The following paper is also not available online for free):
Did Nature Also Choose Arsenic?
International Journal of Astrobiology (2009), 8: 69-74 Cambridge University Press doi: 10.1017/S1473550408004394
Here's the video of the Astrobiology Press Conference (followed by an earlier video from Dutch TV talking about what Felisa hopes to find in her work).
Here's the video, from a Dutch TV program, of Felisa talking about what she is trying to do in her studies...