Life: Not as We Know It!
December 21, 2010 Leave a comment
By Brendan P. Burns
Astrobiology is a field that addresses fundamental questions of our existence, including the origin of life and whether we are alone in the universe. Recent discoveries in this field are rapidly changing our view of the potential for life elsewhere in the universe. New advancements in remote detection technologies have enabled us to identify hundreds of planetary systems similar to our own, and the search for Earth-like planets continues at a breathtaking pace. Of perhaps even greater significance is that we have found life to survive under conditions previously thought impossible. These include microbes flourishing under extremes of pressure on the ocean floor, at temperatures above boiling and below freezing, and at the intense radiation conditions found in outer space. As a result of these fascinating and almost daily new discoveries, our concept of the boundaries of life has altered forever.
The recent findings of Wolfe-Simon et al., (2010) have the potential to rewrite our understanding of biology. If shown to be accurate they will broaden our definition for life as we know it, but would also broaden our search for life elsewhere as well. These authors report the potentially astounding discovery that a novel bacterium can substitute arsenate for phosphorous in macromolecules such as nucleic acids and proteins. The authors used a range of techniques to study elemental composition in the cells, including, radioactive tracer analysis, NanoSIMS, and synchrotron X-ray studies. Basically the authors conclude that they observed intracellular arsenic in protein, metabolite, lipid, and nucleic acid fractions (Wolfe-Simon et al., 2010). As nucleic acids are the building blocks of life, if correct this paper has huge biological, evolutionary, and even philosophical consequences.
One of the biggest questions is if indeed the microorganisms are substituting arsenic for phosphorus in major macromolecules,howare they doing it? With all of the myriadof biochemical reactions thus far known to involve phosphorous (many involving ATP and other cascade reactions), the only conclusion can be this microorganism has completely different enzymes and thus biochemical pathways to any known form of life. This suggests different evolutionary pathways to establish these metabolisms, yet sufficient pressure to ensure they were maintained and not lost in this microorganism (and potentially others?). For example, there would need to be an enzyme or enzymes akin to a phosphatase that could add or remove an arsenate moiety where needed, in addition to the already known arsenite oxidase and arsenate reductase. Thus an organism would haveto possess a very different biochemical apparatus to facilitate the utilization of arsenic in the way they have proposed, and elucidating these pathways(if they exist) is critical to lend support to the authors’ conclusions.
Furthermore, if validated, another obvious evolutionary question is: is this the only example of this ‘form of life’ or are there are similar examples that have survived the ravages of evolutionary pressure? Is it possible that the other known essential elements for life (carbon, hydrogen, nitrogen, oxygen, and sulfur) could also be substituted in addition to phosphorous?
The possibility that silicon could substitute for carbon as the basic building block of life has long been speculated, and if confirmed the discovery by Wolfe-Simon and colleagues adds weight to the the search for ‘alternate life’ supported by different elements. The search for other hypothetical types of biochemistries and even alternate solvents other than water remains an intriguing quest for many scientists to truly understand the ‘limits for life’.
However, it should also be acknowledged the article has (presumably) gone through the correct and rigorous process of peer-review that any legitimate journal would demand. If true, then some of the harsh criticism of Wolfe-Simon and her team is unwarranted. The work by Wolfe- Simon and colleagues could indeed be shown to be wrong, but at the very least it has led to a very useful discussion on the topic between scientists and the need for sound evidence to back up conclusions. Any follow-up papers on this topic would then hopefully be even tighter and allow scientific peers and the general public to be completely convinced by the findings. The implications of this report by Wolfe-Simon and colleagues are obvious and far-reaching. There needs to be rigorous follow-up studies subject to critical peer-review to prove or disprove the claims put forward, and to ensure a healthy debate in the field of astrobiology. It opens up many intriguing questions. Is natural selection universal? Could the universe be filled with failed life experiments based on different elements? Is intelligence inevitable?
May be life just is!!
[Ref: Journal of Cosmology]