Arsenic and Old Lakes

Cary Grant reacts to the press conference from NASA

My day today started with a rather explosive bang. The announcement was made by NASA of a new life form that was initially, in the first few articles I read, presented as the only member of a brand new tree of life. The words ‘shadow biosphere’ were thrown around more than once…

If confirmed, the discovery by Dr. Wolfe-Simon (already mentioned in one of Heidi’s posts) and her team would have constituted discovery a of tremendous importance. Easily Nobel prize worthy and maybe the most significant in the decade.  I did spend some time alternating between looking for more information and running around telling everybody in a state of frantic excitation… pants might have been lost at some point (somebody just mentioned that they were in the lab autoclave, it is nice to put warm clothes on)… That was huge (the discovery).

And this was not, actually, implausible, at all. We know that abiogenesis occurred at least once and occurred pretty fast, in less than 500 million years. We also know from the works on the field of abiogenesis that the biochemistry leading to the primitive blocks of life will spontaneously emerge under quite a variety of conditions.

So it is quite likely that proto-life arose several time on earth. Yet, so far, we only know of one tree of life. We are, as the song says, all connected (by the way, if you don’t yet know the Symphony of Science, you should go and visit this site, it will make you a better person, seriously). Why? Well, it is very possible that earlier attempts got stamped out before they could take root. It is also possible that the conditions, in particular the availability of highly reactive oxygen, are now less favorably. But, mostly, in my opinion, because life, at first, is slow and clumsy, an ugly duckling of life, if you will, a blind, one-legged duckling. And that’s ok, it gets the job done, it swims around, in circle, and survive, reproduce and evolve into something more streamlined and efficient. But what about the next abiogenesis to appear? What about the next blind, one-legged duckling? It now has to swim in water populated by great white, laser-headed sharks. How long do you give the ugly duckling? It will be out-competed at every turns and right out of existence by highly evolved micro-organisms…

Now, we run across uncultivable microorganisms fairly regularly. After all, microbes generally have quite specific nutritious requirement and it often the case that we lose an unknown organism before figuring out how to cultivate it… Some people sometime wonder if some of these organisms might not be uncultivable simply because they are based on a totally different biochemistry, as would be the product of an independent abiogenesis… Further complicating the task of identifying them would be that the main features we use for the identification of microorganisms, such as the ribosomes sequences, would never have evolved. That’s a really cool idea, a whole biosphere, living alongside us, in the shadows (and lookie there who is the supervisor on this work), undetected. A wonderful idea (or not) to think about, but, so far, mostly idle thinking…

Now, let’s go back to the shark bit… If your water is infested by such sharks, where would you go to look for hypothetical remaining ducklings? Quite logically, in water to shallow for the sharks… In more practical term, you’d be looking to places where ‘classical life’ would not be present, or not be performing well enough to out-compete the duckling… The bottom of an arsenic-filled lake, for example…

Now, this is not the only thing that Dr. Wolfe-Simon and her team were looking for… Previous description of her research mentioned extremophiles… Nonetheless, considering some of the more theorical articles she co-wrote, the thought, probably, was on her mind…

Anyway, did they find the ducklings, you ask? Nah, the sharks got there first… It’s a bit disappointing, after all my self-inflicted hype… We could have learned so much from the ducklings… But it seems like the new life form discovered by Dr. Wolfe-Simon and her team is a new member of the Halomonadaceae family, a fairly well known family of bacteria. The team also describes a whole slew of macromolecules that are pretty much the equivalent to what is known on ‘classic’ life, and it seems unlikely that ‘duckling life’ would have evolve them independently…

So the scoop is now about, how the sharks got there. After all, it was to shallow for them, remember? Well, it’s simple; the sharks just had to evolve robot-legs. Obviously.

In other terms, the bacteria evolved not only the ability to survive in arsenic rich environment but were able to incorporate this arsenic and use it instead of the, comparatively rarer, phosphorous… Apparently, as reported, this replacement is pretty thorough…

The idea to replace an atom type by another one of equivalent valence is not particularly new. Indeed, the idea of silicone-based life forms is a staple of science-fiction, but this is, to my knowledge, the first demonstration of the idea… Especially with arsenic instead of phosphorous… It’s really cool… And from what little information is available, the change seems to be systematic across the whole organism. A ground-up solution rather than a few jury-rigged molecules like evolution often privilege…

Now, the “practical” implications might be limited. Phophorous is about one thousand to one hundred times more abundant than arsenic, anyway, so, even if life can replace one by the other, it seems unlikely to do so (the carbon/silicone switcharoo has the same limitation).

Still, the discovery is reeeeeeeally cool, one more illustration of what I call the John Hammond principle: ‘Life will find a way’… and that, my friends, is pure awesome, more awesome, even, and that’s hardly a small claim, than all the laser-headed, robot-legged sharks of the world!

Edited to Add: Since I wrote this post, the actual article has come out and was submitted for the scrutinity of the scientific community, most particularly from Dr. Redfield.

Right now, I still have to check the article (I can’t access it online, yet) so I can’t really comment.

I have to say that I have my own reservation about Dr. Redfield’s own calculation. She calculate that the number of available phosphate atoms contaminating the medium would be within the right ballpark to support the final concentration of cells… But this calculation assume that virtually all the phophate would be harvested by the cells.

That does not work like that, the lower the concentration of an element in the medium, the harder it is to harvest it and the more you have to struggle to keep in in against the diffusion… So there is a lower limit under which an organism can not use some chemicals…

So, yeah, I am doubtful about these calculations…

I wonder, it seems to me like one could replace the arsenic in the medium by a radioactive isotope, maybe some ⁷⁴As, it seems like it has a pretty good half life that’d accomodate or the bacterium’s slow growth…

Then, rinse the medium away real well and see if the bacterium is radioactive… In fact, you should even be able to detect which part of the bacterium is “glowing”, normally, you’d expect most of it to be in the nucleoid region… That’d be a good suggestion that the arsenic has been incorporated in the DNA molecule…

Be Sociable, Share!

•