Life is an amazing thing, and we still have a long way before fully understanding it. Never has this been more obvious in recent times till last Thursday, when a team of scientists successfully challenged the CHNOPS theory that all life is composed mainly of Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorous and Sulfur… (read more about the experiment on the NYtimes)
This might seem like a very insignificant finding to you, an extra elemental component in an organism, so what? Well, this is far from insignificant…
This cute little bacterium has completely shifted what we think life actually is, and where life can exist. The primary way of detecting life is of course locating water, more precisely, liquid water. That’s because most organisms are mostly composed of water. Organisms’ dry weight though is composed of 98-99% C, H, N, O, P and S. That’s why interplanetary probes and the Mars rovers are specially equipped to detect these elements and their combinations, for if CHNOPS are present without other toxic elements, substances or environmental conditions, there is a good chance life may exist in that given area.
The team of NASA scientists were able to extract a bacterial species from Mono Lake in the United States, and after two months of growing the bacteria in an Arsenic-rich (and Phosphorous-poor) environment, observed something truly spectacular… The bacteria “replaced” their Phosphorous components with the abundant Arsenic. Most significantly, in the DNA “backbone” which usually incorporates Phosphorous in the sugar-phosphate genetic polymer backbone.
Arsenic is extremely toxic to multicellular organisms because it interferes with the cell’s ability to produce Adenosine triphosphate (ATP), the cell’s main “fuel”, leading to cell necrosis and eventually multi-organ system failure and of course, death. That is why the notion that life could incorporate Arsenic as one of its essential elements is a very exciting discovery.
Arsenic is directly below Phosphorous on the Periodic Table of Elements, and thus, chemically, behaves in a very similar fashion to Phosphorous. That is one reason why Arsenic is so toxic, it can easily enter cells and cell machinery and ruin them, much like mud in an engine’s pistons.
So, our traditional methods of searching exclusively for life that obeys the CHNOPS theory, crumbles, and endless possibilities, all within our reach, emerge. Arsenic is an abundant element on several rocks in our solar system. Planets and several orbiting satellites have been shown to contain Arsenic, and possibly frozen water, or water buried beneath layers of frozen liquids. In other words, environments similar to the underwater heat vents, where temperatures and toxic substances are as abundant as the native extremophile flora.
An amazing day for Biology, and all sciences, especially on the eve of the discovery that our estimated number of stars is in fact quite underestimated, with the possible total number tripling! All the more probable that we will find life soon, elsewhere =)