New life in arsenic?

Since I grew up in Chuquicamata, the copper mining town in northern Chile, at a time when pollution was pretty high, mainly from the fumes coming out of the copper smelter’s smokestacks, I was always told that I had been exposed to arsenic contamination, at least for the first 18 years of my life.

So you could say I am an arsenic-tolerant life form :smile:

During my time at the Escuela de Injeniería (the engineering school; yes, it’s spelled with a J), I met Don José Tohá Castellá, who was researching biofilter technology for cleaning up pollution, which ended up as an invention called the Tohá System, used to decontaminate water.

It was from this professor that I learned something interesting, and to illustrate it I am going to turn to an old friend of the true nerd (something every self-respecting geek has on a desk, on some wall or printed on a T-shirt). I mean the Periodic Table of the Elements. Here it is, with one touch-up: a little box around two elements, Phosphorus (P) and Arsenic (As):

If you have trouble seeing it, click on the image.

As you can see, phosphorus and arsenic are in the same group of the periodic table (column 15). This version of the table is a bit old: arsenic and phosphorus are nonmetals, but nowadays arsenic is classified as a semiconductor (such is fashion).

The important thing is that this fact, that they sit so close together in the periodic table, tells us these elements share some properties. The most important one, and the one Professor Tohá taught us, is that Arsenic can displace Phosphorus, and vice versa, in the makeup of certain molecules. That is why arsenic is poisonous: phosphorus is one of the essential elements of life, and arsenic, having this ability to displace phosphorus, disrupts biological processes and kills living things.

Rasputin and Coca-Cola

They say that Rasputin, the famous and sinister Russian monk, took small doses of arsenic every day, which made him virtually immune to this poison and terrified his murderers, who couldn’t poison him, adding to his legend.

So it seems you can develop a certain tolerance to arsenic, and if what they said about my hometown is true, the arsenic is in my body. Or was, because according to Tohá, Coca-Cola, which contains significant amounts of phosphorus (in the form of phosphoric acid), displaces arsenic from the body (and with all the Coca-Cola I have drunk, I figure I’m rid of the poison by now).

And all this is because of last week’s announcement of the supposed discovery of a new arsenic-based life form, announced by NASA, which stirred up a lot of anticipation, and even suspicions that it was a cover story to draw attention away from Wikileaks’ CableGate

Alien life

The problem is that several scientists have studied the NASA researchers' paper, and they have been pretty critical. Professor Rosie Redfield of the University of British Columbia published on her blog an analysis of NASA’s work, going so far as to say that if the experimental data had been presented by PhD students to her committee, she would have sent them back to take more careful samples and improve their controls.

There is an assessment of this work in Spanish, published at Amazing.es, written by José Miguel Mulet, professor of biochemistry and molecular biology at the Polytechnic University of Valencia.

The main claim of these NASA researchers is that these bacteria replace the phosphorus in their DNA with arsenic. And that is where the problems are, in the way this claim is demonstrated. I quote Mulet:

“The authors prove it with radioactive labeling and see arsenic accumulating in the bacteria… but they show no direct data on biomolecules containing arsenic, such as a DNA structure solved by crystallography or a mass spectrometry analysis. It is one thing for it to be inside the house, and another for it to be part of the structure like any other brick.”

“There is an earlier experiment that raises suspicion. The cell is able to grow in a phosphate-rich medium with no arsenic… so it does not seem to be an essential element; that is, the biomolecules can incorporate either arsenic or phosphate, a surprising case of such important molecules having alternative compositions. There are no arsenic transporters as specific and efficient as the phosphate ones, among other things because arsenic is neither essential nor that common in the biosphere. So rather than a new form of life, it would be a more flexible form of life. And there are plenty more flexible forms, so it isn’t that new.”

So it doesn’t look like we are facing a new arsenic-based life form (something that would widen the range of possibilities for extraterrestrial life).

The vacuoles, the vacuoles!

But there is another interesting objection that Mulet points out:

There is another detail that has gone more unnoticed and that made me suspicious. According to the authors, when the bacteria grow in an arsenic-rich medium they are larger, because their vacuoles increase in size.

For the less initiated, vacuoles are organelles that eukaryotic cells also have and that serve as the garbage can, among other things. It is where the cell stores everything that bothers it and that it cannot get rid of. This organelle is not very common in bacteria; it is found only in some families such as the sulfur bacteria.

A typical strategy for dealing with a toxic compound is to accumulate it in the vacuole, that is, to take it from the medium and stuff it in the garbage can so it doesn’t get in the way… and it turns out that the bacteria grown in arsenic have a full garbage can, and have also taken up a lot of arsenic. Couldn’t it be that there is a lot of arsenic in the garbage and very little in the DNA? Besides, the increase in vacuole size is a clear sign of cellular stress. We are doing something to those bacteria that bothers them. Any ideas?

So the suspicions about this “discovery” start to grow, because NASA needs to show results to sustain its budgets, so it would not be strange if they had rushed to announce a finding with flimsy evidence, on top of the very unfortunate timing of the announcement, which feeds the conspiracy theories.

But besides, a discovery of arsenic-based life would have shaken the scientific community, and it seems that hasn’t happened. This discovery has been met with great skepticism, and with dissenting voices.

Looks like the arsenic aliens will have to wait.