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Pyrrhotite and the Origins of Life
  
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Cesar M. Salvan
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PostPosted: Aug 29, 2013 11:12    Post subject: Pyrrhotite and the Origins of Life  

The possible role of minerals in the origins of Life has become a serious idea during lasts years. Every day, more scientists working in the field of early evolution are convinced that the History of Life and Mineralogy are connected since the very beginning of prebiotic evolution.

It is not casual that I'm interested in this field of study, due to my formation in both Biochemistry and Geochemistry and Mineralogy. As a biochemist, an important issue has accompanied me since my first’s studies: Why are there FeS clusters in Biology? Why the iron-sulphur proteins are so important in all the Earth's biochemistry, from Archaea to Mammals?

If we turn our view to the most important living beings on our planet, the autotrophs, which generate the organic matter that support the heterotrophs (group in which humans are included), we realize that metals in form of iron sulphide, iron-nickel sulphide, molybdenum-iron-sulphide and tungsten complexes are key players in the central biochemical pathways implicated in the generation of biomass from oxidized carbon forms (carbon oxides) and molecular nitrogen. Other striking feature is the similarity between biological iron-sulphur clusters and the crystalline structure of reduced FeS minerals mackinawite, greigite, pentlandite, violarite and smythite. It is not casual: the crystalline structure are directly related with the electron transfer properties. Well...but, are there an historical relation between the geological iron sulphides and the biological ones?

Is possible that the biological iron-sulphur clusters are direct evidences of the beginning of life? In other words, is possible that living organisms transported themselves the geochemical clues to understand the environment in which life emerged on Earth?

My ideas are not new, and resonated with two hypotheses:
- The model of Gunter Wächtershäuser, based on a key mineral transformation:

FeS (pyrrhotite) + H2S –> FeS2 (pyrite) + heat.

The generation of pyrite from pyrrhotite could give redox energy to an early form or proto-metabolism evolved in the mineral surfaces. But, although thermodynamically possible, it is not energetically possible to couple the formation of pyrite with the reduction of carbon dioxide to organics. Anyway, this reaction could be key in the formation of organics from other gases, as CO or COS, present in volcanic environments.

- The model of Michael Russell, that tries to connect the common biochemical features that links all living beings to the sulphide mineralogy of hydrothermal vents in which there is active formation of iron-sulphur clusters and FeS minerals, as mackinawite, the most important of the simple FeS minerals. We can summarize the precipitation of mackinawite as:

Fe2+ + HS- --> FeSaq (Fe2S2(H2O)4; Fe4S4(H2O)4) --> FeS (mackinawite)

If we have the adequate conditions (disequilibrium, gradients…here the discussion turns complex),the question is if it is possible that these iron sulphur clusters and the formation of solid grains of FeS could drive an early form of metabolism and, hence, a complex system capable of chemical evolution.

My idea is to bind the two models and to find an experimental model that, using natural minerals, could demonstrate that a mineralogy of the origin of metabolism is a reality. So, with the research group I lead. we used the central iron sulphide mineral, pyrrhotite, and metallic iron, possibly a very frequent mineral during the anoxia of the Archaean times. The two minerals evolved in an environment in which both lead to the formation of aqueous iron-sulphur clusters and the transformation of pyrrhotite in pyrite, creating an ancestral oxidoreductase activity.

And it works! The system iron-pyrrhotite could catalyse the carbon dioxide fixation and the formation of a key biochemical molecule, the pyruvic acid, from an ancestral, prebiotic analog of acetyl coenzyme A. This is the first experimental approach using a natural mineral and demonstrates that a geochemical system could play the role of a biochemical system in the very beginning of a complex, pre-living system. How the system evolved and increases complexity? New questions follow each experiment, but the mineralogy of the origin of Life is a real field.

Do you want to know more? You can download the paper in PDF (is open access) here:

Natural Pyrrhotite as a Catalyst in Prebiotic Chemical Evolution

This paper, moreover, is the first scientific paper which references FMF forum, and the pyrrhotite samples used were donated by several FMF-ers. So, I considered interesting to share here the results found.



clusters.jpg
 Description:
iron sulfur clusters
Relation between iron-sulfur cluster Fe2S2 and the crystalline structure of mackinawite. The iron is tetra-coordinated and four water molecules complete the structure of the cluster.
 Viewed:  9090 Time(s)

clusters.jpg



clusters2.jpg
 Description:
The relation between the greigite structure and several biochemical iron-sulfur clusters.
 Viewed:  9102 Time(s)

clusters2.jpg



TOC graphic.jpg
 Description:
The carbon fixation reaction catalyzed by pyrrhotite.
 Viewed:  9089 Time(s)

TOC graphic.jpg



protometabolism.jpg
 Description:
My postulation of the possible first metabolism. The pyrrhotite/iron system catalyzes the boxed reaction. The acetyl-CoA (or its prebiotic ancestor) is linked to the Wood-Ljundhal pathway, in which iron sulfides and W/Mo are key factors. The minerals seems to be essential during the starting of the living systems.
 Viewed:  9095 Time(s)

protometabolism.jpg


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Pete Modreski
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PostPosted: Aug 29, 2013 11:32    Post subject: Re: Pyrrhotite and the Origins of Life  

Very neat, Cesar, and thank you for sharing this with us!

Aside from a first, of citing the Forum in a scientific paper, likely this is also a first for posting bio-mineral-chemical molecular diagrams as images on the Forum!
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John Medici




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PostPosted: Aug 29, 2013 11:59    Post subject: Re: Pyrrhotite and the Origins of Life  

Very interesting, Cesar! It takes me back to my early days as a biochemist (mid-1960's) when I studied extraterrestrial life detection methods and was involved in development of one of them for potential space exploration. Since that time, some (self-taught) mineralogical knowledge has filtered into my life, making it more fun to see both sides of the picture.
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Cesar M. Salvan
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PostPosted: Aug 29, 2013 18:44    Post subject: Re: Pyrrhotite and the Origins of Life  

Thank you for the kind words. Is not easy to find resonances with this pretty complex and 'trans-disciplinary' research theme.

Pete, actually is not the first time posting molecular diagrams on the forum!

see
http://www.mineral-forum.com/message-board/viewtopic.php?p=31256#31256
:))
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Roger Warin




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PostPosted: Aug 30, 2013 03:51    Post subject: Re: Pyrrhotite and the Origins of Life  

Hi Cesar,
This is indeed a beautiful study. It is true that the subject calls scientists from all continents and many disciplines.
You said:
That is possible, the biological iron-sulfur clusters are live evidences of the Beginning of life? In other words, possible living organisms Transported Themselves That the geochemical clues to Understand the environment in Emerged All which life on Earth is?
Yes of course. Atlantic medians are other places than Archean where we detect this new life in a sulfur environment.
But I think life needs foremost a soft chemistry (which can be called biochemistry). In other words, regardless of the oxidizing and reducing agents, they must be able to work with very low energy bonds.
Iron is an oxidant that meets these criteria (its magnetic specifications attest this point), besides its great capacity to enter into organometallic compounds. It is called a transition metal. Its variety of electronic structures proves that. Sulphur also is capable of fines oxidation-reduction reactions, and it can be combined with itself.
From another point of view in meteorites, iron sulfide does appear mainly in the form of FeS troilite (diamagnetic). On Earth, it is essentially pyrrhotite dominates (there is only one exception, the troilite was found in Greenland). Pyrrhotite is Fe (1-x) S and is ferromagnetic, due to the gaps (x is very small). Why this difference, probably because meteorites are from a highly reducing environment. This shows the subtle and important role of iron.
So I would say that iron and sulfur were biochemical precursors, but we also introduce many other heteroatoms in organic chemistry, including phosphorus, oxygen, nitrogen, magnesium, and other elements transition than iron, etc ...
In my opinion, the geological environment you might think "inert" also played a large role in prebiotic synthesis (and perhaps more).
Nature that we admire is really well done. Nucleosynthesis favored essential to life elements (excluding hydrogen from the Big Bang) in preferred quantities. Carbon, oxygen, sulfur, nitrogen, phosphorus ... and even iron elements are preferred by the nucleosynthesis processes of stars.
Many studies are done on so-called primitive chondrites, that is to say carbonaceous chondrites, and the temperature never exceeded 100 °C (far enough away from the Sun). Without going into details, these stones are silicated rocks containing water that has altered (serpentinized) silicates such as olivine and pyroxene in phyllosilicates (there is no amphibole in meteorites from the Asteroids Belt).
These alterations, even under reducing conditions, have produced the same phyllosilicates as those produced by the weathering of Deccan basalts.
Is it a coincidence or a necessity, but these phyllosilicates (or clay) could provide such a support to allow all catalyzed reactions that under normal conditions seem impossible. In particular, these anionic silicated supports capturing active cations can induce such stereoselective catalyzed reactions, which is essential in biochemistry.
Finally, I stress the importance of oxygen. Do not forget that if iron can have a chalcophilic character, it is also a lithophilic element. Always this subtle ambiguity ...
In conclusion, I would add that the couple invoked is a plausible hypothesis, but it is not the main route of birth of life. I wrote these words only to temper the idea about iron-sulfur. They are there to generate any debate.
Roger.
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Riccardo Modanesi




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PostPosted: Aug 30, 2013 06:11    Post subject: Re: Pyrrhotite and the Origins of Life  

Hi to everybody, hi Cesar!
Cesar, if you go further with your experiments, pay attention not to do another Jurassic Park! Hahahahah!
Of course i was joking, but your explaination (supprted also by an experimental basis) is very interesting and understandable even for people who aren't so clever in understanding chemistry!
Greetings from Italy by Riccardo.

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Mark Ost




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PostPosted: Aug 30, 2013 10:04    Post subject: Re: Pyrrhotite and the Origins of Life  

Thanks Cesar

Chemistry was my weakest subject in school! I am now in rehab and should be out in a few weeks. Post traumatic class syndrome. Now I know why I am just a plain old dirt geologist!
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PostPosted: Aug 30, 2013 16:52    Post subject: Re: Pyrrhotite and the Origins of Life  

Very fascinating, Cesar! And a subject somewhat dear to me.
As a student at UBC many moons ago I took a seminar class in paleobiology and the professor gave everyone a list of subjects to study then deliver a seminar on one of the subjects...me he gave a list with only one item on it and, with a big smile, said "...and Mark gets to talk about this subject". The resultant paper and seminar was titled "The First Organisms?" and was primarily based on the work of Cairns-Smith, who looked at the idea of crystallization as the platform for self-replicating molecules. The study focused on clay minerals, however. Easily one of my favourite assignments ever.

I am looking forward to reading this more thoroughly...is your paper available as a pdf? Something I could print and take with me?

Cheers,
Mark
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PostPosted: Aug 30, 2013 16:59    Post subject: Re: Pyrrhotite and the Origins of Life  

Sorry, just saw the link. I was reading the article on my iPhone before and missed it.

Thanks!

Mark
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PostPosted: Aug 30, 2013 19:43    Post subject: Re: Pyrrhotite and the Origins of Life  

Kaolinite and detrital muscovite are important in molecular organization leading to cyclic organic compounds and the evolution of marine chemistry.
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