Earlier this week, an announcement of a press conference today at NASA led to all sorts of speculation as to what would be announced. Based on who was appearing at the press conference, most of the speculation centered around the idea that maybe alien life had been discovered on Saturn's moon Titan. Well, some of the information about the press conference has leaked, and the discovery is much more terrestrial. However, it does have implications for the discovery of life on other planets.
According to Gizmodo and NASA Watch, NASA will announce the discovery of a bacterium in California's Mono Lake that achieves the effect of phosphorylation differently than other known organisms. Instead of using phosphorus, the bacterium uses arsenic, which is usually toxic & deadly to living things. So if life can adapt to use arsenic here on Earth, it makes it possible that life can adapt to live off arsenic (and God knows what else) somewhere out there.
For those that took Freshman Biology, you might remember that 99% of life on Earth (plants, animals, bacteria, etc.) is composed of 6 elements; CHNOPS.
Phosphorus plays an important biological role in the form of ATP (Adenosine triphosphate), which is a cell's "energy currency." ATP is key to metabolic functions, and works by activating structural proteins & enzymes through donating its phosphorus groups.
On the Periodic Table, arsenic sits directly below phosphorus (meaning, among other things, they have the same number of valence electrons). In humans & other forms of life, arsenic can be deadly, since it disrupts cellular respiration by competing with phosphorus & diminishing ATP formation.
An organism that uses arsenic in its biochemistry is "alien" to what is known, since it must have ATP-like molecules with arsenic swapped in phosphorus’ place and because they must have evolved mechanisms such that arsenic doesn’t kill them. All signs point to this announcement being tied to the work of biochemist Felisa Wolfe-Simon, who theorized in the past that the unusual ecosystem in California's Mono Lake could have led some life to follow a different "evolutionary pathway."
From NASA Watch:
An article by several of the individuals (Benner, Wolfe-Simon) who will be participating in the telecon can be found below.
Signatures of a Shadow Biosphere, Astrobiology, Volume 9, Number 2, 2009 via The Smithsonian/NASA Astrophysics Data System (A copy of the full article can be found here.) Authors: Paul C.W. Davies, Steven A. Benner, Carol E. Cleland, Charles H. Lineweaver, Christopher P. McKay, and Felisa Wolfe-Simon
"Astrobiologists are aware that extraterrestrial life might differ from known life, and considerable thought has been given to possible signatures associated with weird forms of life on other planets. So far, however, very little attention has been paid to the possibility that our own planet might also host communities of weird life. If life arises readily in Earth-like conditions, as many astrobiologists contend, then it may well have formed many times on Earth itself, which raises the question whether one or more shadow biospheres have existed in the past or still exist today. In this paper, we discuss possible signatures of weird life and outline some simple strategies for seeking evidence of a shadow biosphere."
Then there is this article by another one of the authors (Wolfe-Simon) dealing with putative life forms that use Arsenic instead of Phosphorus in their biochemistry. Again, the concept of a "shadow biosphere" and thoughts as to whether this can be applied to extraterrestrial locations are discussed.
Did nature also choose arsenic?, International Journal of Astrobiology, Volume 8, Issue 2 via via The Smithsonian/NASA Astrophysics Data System
"All known life requires phosphorus (P) in the form of inorganic phosphate (PO43- or Pi) and phosphate-containing organic molecules. Pi serves as the backbone of the nucleic acids that constitute genetic material and as the major repository of chemical energy for metabolism in polyphosphate bonds. Arsenic (As) lies directly below P on the periodic table and so the two elements share many chemical properties, although their chemistries are sufficiently dissimilar that As cannot directly replace P in modern biochemistry. Arsenic is toxic because As and P are similar enough that organisms attempt this substitution. We hypothesize that ancient biochemical systems, analogous to but distinct from those known today, could have utilized arsenate in the equivalent biological role as phosphate. Organisms utilizing such 'weird life' biochemical pathways may have supported a 'shadow biosphere' at the time of the origin and early evolution of life on Earth or on other planets. Such organisms may even persist on Earth today, undetected, in unusual niches."
Update [2010-12-2 13:58:5 by Rimjob]:
From Phil Plait over at Bad Astronomy:
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Here are the critters in question... Note the scale; a typical human hair is 100 times thicker than these beasties.
The bacteria (technically, the strain GFAJ-1 of Halomonadaceae) was found in Mono Lake, an extremely alkaline and salty lake in California near the Nevada border. And I do mean salty and alkaline: it has about twice the salt of ocean water, and has the incredible pH of 10 (neutral water has a pH of 7, and the pH scale is logarithmic; this means the lake water has the same alkaline strength as commercial antacids). Worse yet, the lake has a high concentration of arsenic, a deadly poison to many forms of life (including us). This makes the water toxic for most living creatures as we know them; for example there are no fish in the lake. However, there are algae, shrimp, and other such flora and fauna.
... including these new microbes. Dr. Felise Wolfe-Simon found them in the mud around the lake, and discovered that not only do they happily live with the arsenic, they’ve actually incorporated it into their biochemistry!
Also, Not Exactly Rocket Science has a more in-depth view of this discovery. It's important to note, that while this bacteria has incorporated arsenic into its biochemistry, it's not dependent on it.
They still contain detectable levels of phosphorus in their molecules and they actually grow better on phosphorus if given the chance. It’s just that they might be able to do without this typically essential element – an extreme and impressive ability in itself.
Nor do the bacteria belong to a second branch of life on Earth – the so-called "shadow biosphere" that Wolfe-Simon talked about a year ago. When she studied the genes of these arsenic-lovers, she found that they belong to a group called the Oceanospirillales. They are no stranger to difficult diets. Bacteria from the same order are munching away at the oil that was spilled into the Gulf of Mexico earlier this year. The arsenic-based bacteria aren’t a parallel branch of life; they’re very much part of the same tree that the rest of us belong too.
That doesn’t, however, make them any less extraordinary.
Update [2010-12-2 14:41:30 by Rimjob]:
NASA's press release (thanks to In her own Voice):
NASA-funded astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.
Researchers conducting tests in the harsh environment of Mono Lake in California have discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic. The microorganism substitutes arsenic for phosphorus in its cell components.
"The definition of life has just expanded," said Ed Weiler, NASA's associate administrator for the Science Mission Directorate at the agency's Headquarters in Washington. "As we pursue our efforts to seek signs of life in the solar system, we have to think more broadly, more diversely and consider life as we do not know it."
This finding of an alternative biochemistry makeup will alter biology textbooks and expand the scope of the search for life beyond Earth. The research is published in this week's edition of Science Express.