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[Music]

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[Applause]

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good afternoon I think it's fair to say

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that most of the microbial cells on this

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planet belong to general for which there

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are no cultured representatives majority

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it might be you know it's been quoted as

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saying maybe as many as 80% or more so

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if you realize that most of the

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organisms have no cultured

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representatives and you want to know

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about metabolism it would help to bring

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them into culture so there are certainly

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other ways to study metabolism but

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certainly having organisms and culture

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is one of the best ways now it's also

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likely I would argue that if there are

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so many organisms that are not yet in

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culture that perhaps some of those are

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doing metabolisms we have not yet

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discovered something that we don't yet

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know about so the idea of finding new

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metabolisms I think is pretty exciting

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one and predicting what those

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metabolisms might be is certainly one

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approach and then to look for those

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organisms one way to predict new

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metabolisms is to use energetics and

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this is something that has been done

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before and that's what I'm going to be

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using in my presentation today before I

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get too deeply into this I want to make

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sure that I say just briefly why I'm

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using catabolism rather than the

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metabolism metabolism sort of a

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catch-all phrase that most people often

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use in place of catabolism but here we

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really mean the energy yielding reaction

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the the reactants going into the

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organism the organism doing its thing

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giving off waste products and the energy

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yield from that overall catabolism

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methanogenesis being an example

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aerobic respiration being example

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separate from biomass synthesis inside

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the cell which would be an AB ilysm so I

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will try to be consistent with

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catabolism but like I said some people

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just end up using metabolism to mean

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catabolism all right so the best example

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I think in using energetics to predict

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metabolisms and I think most people know

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about this one is from Baroda in 1977

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the energetics were not quite done right

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but it didn't matter in this case but in

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the seventy-seven papers a two-page

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paper that had a huge influence he

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basically wrote that ammonium plus

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nitrite going to

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dinitrogen gas and water has a negative

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Delta G zero or here in this Delta g0

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prime of minus eighty Killick eighty-six

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kilocalories so multiply that by four

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point one to get it into joules so the

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argument raised here was hey there's a

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large negative sign on this Delta G

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there must be an organism out there

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doing it well it took almost 20 years

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until high screenings group at the

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University of Delft determined that this

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process was in fact happening and it was

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in fact happening by being mediated by

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microorganisms and then it took another

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you know about ten years or so before

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Marcel Kuiper's at the Max Planck

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Institute found that anammox which was

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then later termed was actually a very

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common process in natural environments

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and now we talk about all the time as if

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we always knew it existed but in 77 it

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was a thermodynamic prediction so I want

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to use that same approach and think

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about a few other new metabolisms so

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going back to this Anna marks idea you

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see there in that green circle in the

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middle that's basically what Baroda

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based is prediction on and a couple of

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things here to note one is that of

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course thermodynamics or in this case

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Delta G calculations are temperature

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dependent so in some cases the

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temperature dependence is pretty minor

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in some cases that's pretty good or

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meaning pretty pretty dominant sometimes

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the you know the curve goes down

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sometimes goes up so we need to think

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about energetics in terms of temperature

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as well as pressure but pressure is a

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little bit less of an effect unless you

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get to really high pressures alright so

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a temperature dependent function the

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other thing to think about is that it's

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Broudy used a little circle above the

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Delta G so use only a standard state

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energetics again with Anna marks it

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didn't really matter but in reality we

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want to use the chemical environment to

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really get at the real energetics and

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that's a cue term on the right hand side

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of the equation so I've got up here a

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low energy and a high energy example so

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I mean just walk through that really

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briefly the low energy example so that

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blue curve means that there's very low

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concentrations of ammonium very low

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concentrations of nitrites all the

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things on the left hand side and high

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concentrations of the product so

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something like maybe 0.78 bars of

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nitrogen like atmospheric that would be

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a low energy example

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a high-energy example would be opposite

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high ammonium high nitrite low-end to

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content and you can see that the

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chemistry and this is not just randomly

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picking the most extreme numbers these

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are geo chemically reasonable

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concentrations that I've chosen to put

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into the low energy or high energy

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example the point is that there's a

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temperature dependence and as a that can

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be quite a big dependence on the

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energetics coming from the chemical

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environment all right so that's anammox

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now here I've got three examples of

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either unknown or little-known potential

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always remember these are potential

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metabolism so catabolism sorry so in

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this case it's a ferric iron mineral or

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mixed iron valence a mineral magnetite

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being reduced with hydrogen to make

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ferrous iron and then protons and water

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to balance the reaction so delta g r0

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sitting there about minus 100 kilojoule

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with not much of a temperature

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dependence now I want to introduce

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briefly this this prime next to the

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Delta G zero right so this is known as

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the biological standard state and lots

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of people know what this is for those

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who don't it basically says that the

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system is at neutrality so the proton at

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least at 25 degrees would be a 10 to the

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minus 7 instead of the 1 molar or 1

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mol/l unit that's used generally for

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standard states so you can see here

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there are 6 protons in the reaction and

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if you go from 1 molar to 10 to the

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minus 7 7 or as a magnitude raised to

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the sixth power yeah that's going to

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have an effect on your energetic so

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that's why that curve moves up by over a

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hundred kilojoules in this example if

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you consider the low energy example that

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I mentioned before again that would mean

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in this case low concentration of

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protons or in other words a basic system

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high pH system low hydrogen

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concentrations and high fares iron

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that's where the energetics would be and

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would be above zero and organic not a

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good potential metabolism or catabolism

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however if you consider an environment

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that's acidic so high proton activity

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high hydrogen low ferrous iron then you

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can actually see that there would be

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somewhere on the order of minus 50 to

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minus 20 kilojoules per mole

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of electron transferred over this

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temperature range so certainly in the

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low temperature range in an acidic

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environment with high hydrogen this is a

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potential catabolism here's another

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example so this would be a new type of

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methanogenesis if you want to think of

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it that way co2 and ammonium going to

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methane and n2 again protons and water

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to balance the reaction the Delta g0 is

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incredibly boring here as a function of

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temperature it doesn't do much as

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sitting there about 13 and a half 14

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kilojoules per mole electron transferred

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if we then again consider the biological

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standard stage you know huge effect

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again again there are eight protons in

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the reaction so changing it from one

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molar to ten to the minus seven and then

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raising it to the eighth power has a

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huge effect what about when you also

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then include then the environment I'm

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not showing the low energy example here

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because it was endergonic so above that

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that zero line the whole way but at high

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co2 high ammonium low end - and low

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protons so again in a basic or like

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alcholic system there is a small amount

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of energy here now I want to remind

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people these reactions are written well

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the energetics are written in terms of

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kilojoules per mole electron transferred

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so these are all normalized - that the

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reaction as written here is a 24

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electron transfer reaction so for this

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reaction you'd have to multiply the

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energetics by 24 and then you would see

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that this you know quite a bit of energy

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to be had for this potential catabolism

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so the one I want to really focus mostly

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on the one we're most excited about is

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this one here so this is called sulfur

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comprar Porsche nation lots of people

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don't know that term but people have

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certainly heard the term sulfur or other

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or other element disproportionation so

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that would be the back and reaction here

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alright let's start with sulfur

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disproportionation elemental sulfur

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intermediate oxidation state going to

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something more reduced sulfide and more

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oxidized sulfate people know that the

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back reaction happens and the organisms

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that can do that but the back reaction

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has a positive Delta g0 so again it's a

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it's just evidence that the chemistry

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the system absolutely is essential in

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getting the energetics right we're

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interested in the forward reaction as

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and here calm proportion Asian sulfide

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plus sulfate protons for the balancing

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to make elemental sulfur Delta G zero

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for this reaction again not very

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temperature dependent sitting down there

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about a minus 120 if you wanted to

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consider the biological standard state

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that's what it would look like as a

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function of temperature again the

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low-energy example won't work but in a

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system of high sulfide high sulfate and

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low pH this is a potential catabolism

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you know especially at low temperature

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main as you know in the 0 to 50 degree

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range let's say this is the same

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reaction but plotted slightly

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differently so pH on the y axis going

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from 0 to 7 temperature just up to a

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hundred degrees and then color coded

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basically on these temperature profiles

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with a dark blue minus 50 kilojoules in

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the greens minus 30 the yellows minus 10

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and the yellow to white transition being

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equilibrium so you can see here again

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that you know in the in acidic range pH

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1 2 3 somewhere in that neighborhood and

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there's certainly plenty of acidophiles

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that can handle then in environments

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with low high sulfide high sulfate this

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would be an energy yielding reaction and

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energy yields that are not unreasonable

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10 20 30 40 kilojoules we heard from

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Sanjoy this morning that sort of 10

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kilojoules per moles often a cut-off

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anything more than that might be

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reasonable and here we're certainly

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dipping into the 30 to 50 kilo Joule per

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mole range so what kind of environments

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might you find this metabolism of

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metabolism in so that's so that in the

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next step you predict a new metabolism

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then you go hunt for them and my

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graduate student heidi Aronson is going

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to be going off to the frasassi caves

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system with Jen Mack alladhi in about

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two weeks to hunt for these organisms so

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why frasassi well it's an environment

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where there's it's a cave system in

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northern Italy it's it's a cave system

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where this gypsum so sulfate minerals

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precipitating there's the smell of

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hydrogen sulfide in the cave and they've

290
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measured PHS as low as one and two so

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that's the kind of environment that

292
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would seem to be ideal for this but it's

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the only kind shallow sea hydrothermal

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systems where I've worked for quite a

295
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while I might also be good hunting

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grounds you have a marine system so

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generally high sulfate you have organic

298
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gases including sulfurous gases coming

299
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into the system high sulfide in many

300
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cases we've measured two to

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two-and-a-half volume percent h2s and

302
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the gas phases of the gases in the gas

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phase some of the systems can be quite

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acidic that might work acid mine

305
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drainage sites might also have some

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combination of the high sulphate high

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sulfide low pH that would make them

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attractive ask the sulphate crater lakes

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and so on and so forth so again so they

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just drive this point home we're looking

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strictly from a chemical geochemical

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thermodynamic standpoint are there redox

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reactions which under certain reasonable

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geochemical environments would be have

315
00:12:13,640 --> 00:12:10,950
it would have an Delta G that's that's

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negative and would it have a Delta G

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that's negative enough to then start

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using that as a sort of a first step in

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looking for organisms then the hard part

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really begins getting the samples

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bringing them into lab trying to culture

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them and so on and so forth so this is

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absolutely not saying these metabolisms

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are Kaplan's exist well that these

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organs exists is really just the first

326
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step it's very analogous to Baroda

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saying hey here's Anna marks maybe

328
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there's something out there I'm hoping

329
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it won't take twenty to thirty years

330
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until we find these I'll be dead but you

331
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know would be nice if maybe you know in

332
00:12:53,720 --> 00:12:52,380
the in the in in the meantime we could

333
00:12:55,460 --> 00:12:53,730
find them a little bit more quickly than

334
00:12:57,950 --> 00:12:55,470
we did for animals but remember animal

335
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walks is nitrogen calm proportion Asian

336
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so sulphur comprehend a shoe should not

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be that weird a concept and with that

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I'm happy to take questions if there are

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00:13:22,120 --> 00:13:14,170
we have time for a few questions for

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Yann I had a quick question for you Yann

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so are these so when you're going out

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looking for these organisms that might

343
00:13:29,380 --> 00:13:27,050
be conducting these metabolisms the calm

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00:13:32,020 --> 00:13:29,390
proportion Asia etc are these are

345
00:13:33,880 --> 00:13:32,030
primarily incubation based analyses

346
00:13:36,190 --> 00:13:33,890
that's certainly what we're starting so

347
00:13:38,500 --> 00:13:36,200
what what Heidi has done is used the

348
00:13:40,510 --> 00:13:38,510
chemistry of the system in this case the

349
00:13:44,260 --> 00:13:40,520
frasassi caves system based on previous

350
00:13:46,120 --> 00:13:44,270
studies analyses to design growth media

351
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that mimicked as closely as possible the

352
00:13:50,800 --> 00:13:48,980
system but we actually don't mimic

353
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perfectly we do give it a sort of a

354
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little extra boost we give it perhaps a

355
00:13:55,960 --> 00:13:53,660
little bit more sulfate a little bit

356
00:13:57,580 --> 00:13:55,970
more sulfide or you know vary the pH a

357
00:13:59,800 --> 00:13:57,590
little bit more than we might find in

358
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nature so it's not just saying exactly

359
00:14:04,120 --> 00:14:01,940
the things we've measured is the medium

360
00:14:05,830 --> 00:14:04,130
we're using but it's based on that and

361
00:14:08,140 --> 00:14:05,840
then just initially at least giving them

362
00:14:09,580 --> 00:14:08,150
a little bit extra push by giving them a

363
00:14:12,010 --> 00:14:09,590
little bit more the reactants then maybe

364
00:14:14,650 --> 00:14:12,020
is in the system and then perhaps you

365
00:14:23,650 --> 00:14:14,660
know playing off of that yeah but yeah

366
00:14:26,410 --> 00:14:23,660
it's culture based at first Pete thanks

367
00:14:28,900 --> 00:14:26,420
yeah that's super cool I am I think that

368
00:14:30,580 --> 00:14:28,910
if you're staying alive means not

369
00:14:34,080 --> 00:14:30,590
finding these and a bunch of us are

370
00:14:36,400 --> 00:14:34,090
gonna try to avoid finding them the so

371
00:14:38,200 --> 00:14:36,410
something a question for you as a

372
00:14:41,200 --> 00:14:38,210
forgive me if it's a bit out there but I

373
00:14:44,050 --> 00:14:41,210
am curious how do you think this plays

374
00:14:45,720 --> 00:14:44,060
out in terms of the prevalence of calm

375
00:14:49,390 --> 00:14:45,730
proportion nation over evolutionary time

376
00:14:53,020 --> 00:14:49,400
like in a point in time where we may not

377
00:14:55,780 --> 00:14:53,030
have had these oxidized sulfur species

378
00:14:57,580 --> 00:14:55,790
right or nitrogen species do you do I

379
00:14:59,610 --> 00:14:57,590
mean is it too heavy-handed to assert

380
00:15:01,570 --> 00:14:59,620
that this might be a slightly younger

381
00:15:03,670 --> 00:15:01,580
metabolic capacity do you see where I'm

382
00:15:05,050 --> 00:15:03,680
going with this yeah I mean if you

383
00:15:06,850 --> 00:15:05,060
didn't have sulfate you're not gonna

384
00:15:08,890 --> 00:15:06,860
have sulfur comprar partion nation right

385
00:15:12,160 --> 00:15:08,900
so would you have had sulfate until the

386
00:15:14,050 --> 00:15:12,170
system was you know quite oxidized what

387
00:15:16,540 --> 00:15:14,060
it would have been you know sulfate

388
00:15:20,020 --> 00:15:16,550
after the sort of rise of oxygen if you

389
00:15:21,940 --> 00:15:20,030
will it because it requires for the

390
00:15:25,660 --> 00:15:21,950
sulfur example quite high cost

391
00:15:28,870 --> 00:15:25,670
of sulfate as opposed to the the Anna

392
00:15:30,370 --> 00:15:28,880
marks example that may be the case so we

393
00:15:31,930 --> 00:15:30,380
have not thought about we're not saying

394
00:15:34,120 --> 00:15:31,940
that these are necessarily early

395
00:15:36,240 --> 00:15:34,130
metabolisms anything like that it would

396
00:15:38,829 --> 00:15:36,250
be fun to play around with that idea I

397
00:15:42,040 --> 00:15:38,839
think for Anna marks it's not a problem

398
00:15:43,930 --> 00:15:42,050
because nitrite or nitrate are better

399
00:15:45,519 --> 00:15:43,940
electron acceptors and sulfate is so

400
00:15:47,110 --> 00:15:45,529
which means to an organ for there to be

401
00:15:48,910 --> 00:15:47,120
energy there has to be quite a lot of