Methanogens

[valhalla]

I am involved in a discussion concerning Methane on Mars...I suppose it being a hot topic on Mars at the moment.

The contention is my adversary insists that the lack of detected Ethane is indicative of a non-biological source in the detected Methane signature from orbital as well as Earth based observations.

 

He claims that ALL Methanogens produce Ethane as a by-product of metabolism, that it is more reliable then just a methane C-12 signature, that Ethane is easily detectable with the tools at our disposal, and the absence of the Ethane signature is the smoking gun in a denial of no bacteriological life on Mars.

I am no Bio-Chemist, just a lowly HNC on Inorganic Chemistry.

 

Is the 'ALL Methanogens produce Ethane' contention correct.

The internet admits that SOME strains of Methanogens do...but I cannot find any that specifically do not, and not the expected C2H6 yield when they do!

 

Furthermore I think the lack of detected Ethane in planetary atmosphere where there is little to no extended obvious hydrocarbon activity detected is not quite the death knell to biological life my adversary claims.

 

I am prepared to be in error, is there a definitive view on this in the bio-chemical world?...Is Ethane an essential signature in possible life?

Any replies appreciated!

[Moontanman]

I am involved in a discussion concerning Methane on Mars...I suppose it being a hot topic on Mars at the moment.

The contention is my adversary insists that the lack of detected Ethane is indicative of a non-biological source in the detected Methane signature from orbital as well as Earth based observations.

 

He claims that ALL Methanogens produce Ethane as a by-product of metabolism, that it is more reliable then just a methane C-12 signature, that Ethane is easily detectable with the tools at our disposal, and the absence of the Ethane signature is the smoking gun in a denial of no bacteriological life on Mars.

I am no Bio-Chemist, just a lowly HNC on Inorganic Chemistry.

 

Is the 'ALL Methanogens produce Ethane' contention correct.

The internet admits that SOME strains of Methanogens do...but I cannot find any that specifically do not, and not the expected C2H6 yield when they do!

 

Furthermore I think the lack of detected Ethane in planetary atmosphere where there is little to no extended obvious hydrocarbon activity detected is not quite the death knell to biological life my adversary claims.

 

I am prepared to be in error, is there a definitive view on this in the bio-chemical world?...Is Ethane an essential signature in possible life?

Any replies appreciated!

 

It would appear that your friend is mistaken, the production of ethane from methanogens is highly limited according to everything I could find with google (google is your friend)

 

http://en.wikipedia.org/wiki/Methanogen

 

Looking for articles linking methanogens to ethane came up with this thread as the fifth result.

 

http://www.google.com/#hl=en&output=search&sclient=psy-ab&q=Methanogens+ethane&oq=Methanogens+ethane&gs_l=hp.12..0i13i30l3j0i8i13i30.3275.10596.0.33543.7.7.0.0.0.0.265.1020.2j3j2.7.0.les%3Bcqrwrth..0.0...1.1j2.o4bb7_TG5Hg&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=32142d4a7aa176f8&bpcl=37189454&biw=1152&bih=777

 

This is a paper that details this reaction.

 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC243973/

 

I would suggest you ask your friend for his source on his assertion.

[valhalla]

Thanx Moonanman,

 

Yes those were some of the few articles I found.

 

There are tantalising mentions that 'Some Methanogens' indeed are involved in Ethane production, but yield and specifics beyond those statements are very vague.

Mainly it is a managed production and a recounting of various pathways observed from other hydrocarbon reactions.

 

And any mention of Ethane being a signature for life besides Methane measurements is suspiciously absent in any link.

 

My adversary's quote was along the lines that 'Methane is one thing but where is the ethane signature...there has been none found and ALL Methamogens produce it' ...he then went on to declare that if life is found it would be nothing like the Methanogens we are familiar with, he basically accused me of making the concept up...weird!

 

I think I will have to demand citation from my adversary because it is the first time I have ever come across such a claim.

I was hoping to be a little better armed with some facts because as I mentioned Bio-chemistry is not my area at all.

But this claim did ring rather odd all the same.

Again thanx for your time...appreciated.

 

As it happens I think that this will be a mute point on Friday anyway when NASA issue a update on Curiosity's research into the Martian atmosphere.

Methane levels and a possible isotopic result on the carbon found should be in the detail...of course I am hoping for a C-12 predominance...cos then it really looks like we haz uz some bugs

 

 

 

Edited November 1, 2012 by valhalla

[Ophiolite]

In addition to the information you have gleaned and Moontaman has supplied, you should point out to your friend that there is no requirement for Martian methanogens to behave like terrestrial ones, or to have the same metabolic pathways.

 

I am from that minority who think the Vking labelled release experiment probably did detect life. However, I find the atmospheric methane no more than intriguing: I don't think it adds to tthe probability of Martian life.

[Jens]

(In addition to all that have been said before...) The biochemical pathway from CO₂ to methane directly reduces the single carbon molecule step-by-step with aid of different specific coenzymes to CH₄. So it is a complete one carbon pathway. Only electrons are transferred from H₂. It is not a cyclic pathway with involvement of tow-carbon compounds. Reduction of CH₃OH or other methyl compounds uses the same pathway. Even CH₃COOH is transformed into CH₄ and CO₂. Only one carbon is reduced and the same one carbon pathway is used. This means there is no obvious reason why all methanogens should produce CH₃CH₃ on earth. It looks quite the opposite. And definitely there is no reason whatsoever, why a CH₄ producing pathway of life on another planet should always produce CH₃CH₃.

Edited November 1, 2012 by Jens

[valhalla]

I am from that minority who think the Vking labelled release experiment probably did detect life. However, I find the atmospheric methane no more than intriguing: I don't think it adds to tthe probability of Martian life.

 

For my sins...so am I...

I rather conclude that life was not expected in any form either fossil or alive by the majority of the scientific establishment back then, the Viking results threw them a curved ball and they looked for anything to discount the anomaly!

Makes you think they put the experiment package on Viking to actually discount not confirm the idea!

Blaming 'cleaning fluid' was, I think a way out of an embarrassment.

Can you imagine the reaction in the media not to mention the overwhelmingly theist attitude in the USA back then, they would have been slaughtered, and probably hung out to dry as well as a probable panic stations in the society.

 

Phoenix was a breath of fresh air and coupled with the Methane blooms tracked over a decade...it kindda points to some activity, I go for Microbiological, but even if it was geologic that is still a fantastic discovery.

 

Anyway I rather gather a Carbon mass spec to categorize the isotopic ratio has been accomplished on the rover...they were hinting at it obliquely about a week ago, I think they got a result and are releasing the data tomorrow...we shall see!

If C-12 predominates methinks we will not see Kansas again in our lifetime but at least the Exo-biologists come of age and get an ET to practise with...if indeed it is extraterrestrial that is

 

Jens thanx..

 

That was more or less what I was clumsily trying to articulate in this debate I am involved in...you nailed it and I thank you for that!

[Jens]

A more general statement for your topic:

In biochemistry the enzymes are typically very specific and side products are quite rare.

However, if the molecules become very small and uncharged, differentiation becomes more difficult. So there might actually be cases in which all life forms even, if evolved completely independent run into similar issues and similar side products:

The best example is probably the nitrogen fixation. The enzymes making NH₃ out of N₂, have a severe problem, if O₂ is present: N₂ and O₂ are very close to each other in size and charge distribution and O₂ is very reactive while N₂ is the exact opposite. This means any form of enzyme will have this issue and probably similar side reactions.

 

Back to the original question:

There is a point I have not seen in my last post:

The CH₃CH₃ side production in question probably goes as follows (CoM = Conzyme M):

CoM-S-CH₃ gets only one electron transferred (dissociation of the methyl group before it is reduced to methane) and lead to

CoM-SH + ^.CH₃

Two of those radicals formed combine to CH₃CH₃ .

So in case this is a chemically very difficult issue to transfer both last electrons to form methane, it might actually be a point. I can check this out in more detail on saturday.

Edited November 1, 2012 by Jens

[Jens]

I have found the following reference:

Crystal Structure of Methyl Conzyme M Reductase

So yes, the proposed reaction mechanism is via a methyl radical probably bound to an Ni atom (of coenzyme F430). If the last electron transfer fails two of those methyl radicals can combine to ethan (but might very well react with H₂ present in the environment (note there is never O2 in evironments in which there is methanogenesis).

 

In the literature it looks more that ethane is produced if human-made halogenated 2-carbon compounds are in environments where methanogens live.

 

So assuming that extraterrestrial life always must produce ethane to me still seems too far fetched:

- it does not seem to be proven that ethane it is always produced on earth as a side reaction (unless your collegue has more input)

- Even if this is true, another coenzyme used in extraterrestrial life forms might actually prevent methyl radical release (or the reaction with another substance so that no ethane is released).

Edited November 3, 2012 by Jens