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[Music]

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[Applause]

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my name is Sandra I first want to

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acknowledge some of my co-authors the

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notorious story hauler toe McCallum at

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Cibola LASP and mark Alperin at UNC

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Chapel Hill also and acknowledged my

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funding source Rock powered life not

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only for money but for their patience

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and building a very cool community

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around subsurface life so Rica this

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morning and nor EHS now made a really

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good explanation as to explaining the

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value of subsurface biology or geo

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microbiology to assess the possibility

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of life on ocean worlds so that's what

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I'm really interested in is how can we

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quantify this concept of habitability

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for methanogens and it's important

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because in the absence of oxygen at

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least on earth these these subsurface

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environments I extremely devoid in

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energy there's a really low energy

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environments rights about six orders of

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magnitude that separate that energy

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available to photosynthesizers compared

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to chemo synthesizers so it's really

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important to us as well the energy in

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the subsurface and the disconnection

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between geology and biology has been

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made by many people during this

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conference with this conference in

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particular connecting the process of

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serpentinization which is a reaction of

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water and rocks certainly not limited to

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the earth and one of the cool byproduct

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of this of this geo chemical reaction is

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the production of hydrogen and it also

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produces very alkaline water and then

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the coupling is obvious by the fact that

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hydrogen is a great electron donor and

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bugs I figured out how to use it to

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reduce co2 to methane but Deb Kelly

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warned us in some of our lost city

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papers that organisms living in vents so

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in this case lost city type vents must

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be adapted to a low dissolved inorganic

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carbon co2 poor and hydrogen rich

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environment so why is it why is it co2

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poor well the reason is is that carbon

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speciate s-- as a function of pH so in

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this plot on the x axis is concentration

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of carbon the numbers don't mean much

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for this for this particular talk and on

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the x axis is pH so in regions of acidic

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fluids carbons preferentially speciate

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s-- into co2

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whereas in circle neutral pH carbon

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professionally speciate sin to bicarb

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and in alkaline pH covering

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preferentially speciate sin to carbonate

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so in alkaline environments that such

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that accompanied those of active

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serpentinization the co2 concentrations

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are really poor and is that important

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well limiting illustrate this in another

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plot here I plot hydrogen concentrations

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on the y axis and co2 concentrations on

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the x axis and these black squares here

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are kind of a collection from the

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literature of sites of methanol Genesis

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right rumen goats rice soils swamps the

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lake sediments just kind of a collection

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and they all plot down here high co2 low

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hydrogen where as sites of active sand

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potent ization again a collection from

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the literature chromo velocity or mine

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cedars and Tablelands and they all have

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high hydrogen Moore s and very low co2

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so all everything that we know about

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methanogenesis is done with bugs that we

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can sample easily and those are hydrogen

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limited whereas when we seek to

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understand life in in serpentinization

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environments while those are hydrogen

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limpid and that's important difference I

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also plot up here a hypothetical culture

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of methanol methanogens typically when

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we put them in test tubes we blast them

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with a lot of co2 a lot of hydrogen so

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that they're happy so again what we know

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about metallic jeans comes from a

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physical chemical space that is not

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expected in serpentinization

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environments so then how do we assess

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the energetic the energetics available

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for these systems allow me a quick 30

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second bio energetic primer some of you

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may be astronomers in the room I don't

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know but imagine a bug as a light bulb

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on the sea floor and the reason why it

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shines is because it's connected to a

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battery a battery provides a voltage

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that enables the flow of charge carriers

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or a current the product of the voltage

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and the current is the power and in

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natural environments the analogy is such

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that the voltage is the Gibbs free

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energy that we can calculate from the

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local conditions and so it keeps free

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energies and energy made available by an

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environment for the bugs to do work

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right so if we plot the same sites as I

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showed earlier just was there Delta G so

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on the y-axis and the only axis is the

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is the Gibbs free energy here which is

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the negative of the affinity the early

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earlier this week there are many talks

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about the affinity is the same thing as

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it gives free energy just a sinus worked

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anything that's more negative than about

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-10 is considered energetically

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favorable right so in black again is our

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sites of classical methanogenesis all

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below minus 10 all very happy and

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quantifiably favorable for

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methanogenesis using this metric and the

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sites of active serpentinization

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are some of them are even more favorable

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for for using this metric for for

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methanogenesis

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but this is not the full story right you

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cannot describe the electrical

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properties of a light bulb with voltage

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alone you need to understand the current

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as well so the point of this

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presentation perhaps is to encourage all

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of you who think about energetics in

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these natural systems to go beyond delta

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g to to to assess whether or not an

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environment can host life so let me a

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hammer that one more time delta g is

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calculated from both values only right

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but cells consume carbon and hydrogen so

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the concentration inside the cell is

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different than the BOK therefore the

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delta g inside the cell is also

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different but a cell is complicated

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right how do you take into account what

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is the physics that brings the material

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inside the cell what about the effects

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of a cell membrane what about the

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enzymatic rates that convert the carbon

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from co2 to methane all those things are

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important that so that's where systems

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biology comes in handy so we've used a a

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single cell reactive transfer model

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developed by outrun and Haller in 2009

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that takes diffusion as the as the mass

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transport mechanism because we're

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working with simple molecules like co2

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and hydrogen they just diffused through

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the through the membrane the reaction

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rates are simulated using Monod kinetics

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that's the plot on the right I'll talk

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about in a sec and we can take into

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account the the membrane matter is kind

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of slows down the diffusion process so

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the the the the reaction rates is kind

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of the Monod kinetics reaction here you

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can see that enzymes saturate on the x

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axis is the concentration on the y axis

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is the rates this is the same plots to

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illustrate that is only so much pizza

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you can feed graduate students before

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they saturate right

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so on the x-axis is is a pizza on the

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y-axis here is that rate at which they

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can eat it the km here is the kinetic

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parameter also known as the the budget

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of the department so from what they see

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I'm taking this analogy way too far

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sorry but anyways the the curve the grad

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student and the and the met an engine is

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the same right just the the kinetic

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parameters are different for its reasons

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so if you take this this this is

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enzymatic rates that's the current right

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the amount of material going into the

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cell per unit time so multiply that by

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the Delta G that's inside the cell you

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get a power so instead of looking at

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Delta G from the bulk environment alone

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you can look at energetics from a 2deep

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2deep perspective on the x-axis is the

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same as before that delta g then on the

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y-axis is that power I was telling you

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about and this changes the story a

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little bit right what you can see here

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is all the sites of classical

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methanogenesis are on the right of a

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boundary and on the sites of actives

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important ization on the left and this

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boundary here is is a measurement of

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minimum flux to enable biological

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turnover and calculate it completely

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independently from sulfate reducers in

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the Aarhus Bay from in up holler and

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your consent 2013 so this is a very

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different conclusion than looking at

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just delta g alone right looking at

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delta g alone sites of actives and

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fertilization were awesome for life

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using this perspective you don't expect

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methanogens to be to be present in in

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sites of active synchronization so so

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how do you reconcile that so there's a

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great talk earlier this apps icon by

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Emily Krause who shows that there is

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such methanogens so so how do you

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reconcile the two

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so before we try and think about that

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let me just make two points regarding

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the Gibbs free energy first hi hydrogen

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in supermans in serpentine izing systems

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can kind of fool you right today's they

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are from that perspective alone the

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these sites are energetically favorable

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however when thinking about the power

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requirements of a cell then the the

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energy use scenario is

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different so how did how do we then

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reconcile the results with observation

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of meth engines in serpent rising

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systems or he comes a disadvantage of

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giving a Friday talk is that you have to

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accumulate everything that comes during

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the week and it can alter your

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conclusions a little bit so yeah so so

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so to reconcile this we can use the same

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modeling approach that we that I showed

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you earlier

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what if methanogens had enzymes that

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were on the on the on the membranes

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right instead of diffusing the material

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inside the cell they would had those

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enzymes that would translate the co2 to

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methane on the cell on the cell itself

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and preliminary calculations showed that

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that improves things about 20% right

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which is not enough to talk to to cross

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that threshold alternatively the cells

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could be using bicarbonates that could

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enter the cell through through porins

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through ion channels bicarbonate is

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charged so I cannot just diffuse inside

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the cell so those pH inside the cell is

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neutral roughly so the speciate the by

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covenant would speciate back to co2 so

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that could be an enhancement of co2

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inside the cell but once you have co2

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inside the cell that's a higher

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concentration and outside it diffuses

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right back out and not useful for for

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methanogenesis so that doesn't seem to

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work either we're exploring other

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solutions like formate and acetate and

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even co2 there was a poster by Jackie

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cordial using meta genomics where she

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found her own to butcher her science

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carbon monoxide dehydrogenase in hermit

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metagenomes so maybe that's that's an

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avenue as well or there's this kinetic

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parameter that might be different right

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in the kinetic parameters was the one is

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the grad student plots the one we chose

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for the model is from the literature and

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the literature value is found from sites

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of active metallurgist metal meth an

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agenda that we know today but remember

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this plot I showed in the beginning was

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hydrogen on the y axis and co2 on the x

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axis here I plot that km value that

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kinetic parameter for co2 and hydrogen

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and the equation for power is in fact

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inversely proportional to the sum of

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that km plus co2 now for sites of active

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methanogenesis

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this ratio is controlled by the

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concentration of co2 alone right you

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could increase the power by decreasing

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that km but it won't do much because

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that ratio is set by the concentration

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of co2 for sites of kind of classical

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methanogenesis however that's not the

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case for sites of active

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serpentinization right that ratio is

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actually controlled by the km value

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because the co2 is so small so you can

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perhaps think that the bugs have figured

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out how to drop their their km value by

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say an order of magnitude because from

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that ratio that would increase the power

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by an order of magnitude and so I I read

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it those redid the same calculations

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with Delta G on the y-axis and power on

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the x-axis here that's that same limit

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from Alperin and Jurgen sin 2013 but

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which is different kinetic parameter and

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you can see that some of the sites of of

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activists urbanization do become

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habitable from this perspective right we

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have almost all of them except for two

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from LA City one from Amman and so we're

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getting very close to that threshold so

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perhaps that's an avenue right bugs have

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evolved to have a different kinetic

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parameter that we do not observe in

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cultured experiments because we culture

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from sites that we can actively sample

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them so this is kind of the two plots so

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you can see with the km from the

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literature versus kind of playing with

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playing with the the that km values to

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shift a little bit that perspective so

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that's it I don't think there's any

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conclusions we can do at this point but

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the energetics of an environments that

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can host or patent ization that can host

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methanogens

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through personalization is just I think

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more tricky than has been traditionally

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thought of thank you

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time for a question for sunshine

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pressure I don't know I'm a it's a good

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question so the question is how does

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pressure affect the the enzyme kinetics

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I don't I've not seen a study that took

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spent methanogens and puts them under

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00:13:33,800 --> 00:13:32,250
high pressure or net and sees what the

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rates are different compared to

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traditional hemostats I think there'll

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be a really cool experiment harder but

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really cool experiment yeah I don't but

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that's in the literature I don't have

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hi Sean

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00:14:06,440 --> 00:14:04,560
hey thanks for the great talk I had a

348
00:14:08,060 --> 00:14:06,450
question about where the km value comes

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00:14:09,980 --> 00:14:08,070
whether or not it it's from a mat

350
00:14:12,650 --> 00:14:09,990
antigen with cytochromes or one without

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00:14:14,000 --> 00:14:12,660
cytochromes and that that's a really

352
00:14:16,160 --> 00:14:14,010
simple question you can answer them a

353
00:14:18,530 --> 00:14:16,170
word but the other point I wanted to

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00:14:20,870 --> 00:14:18,540
raise was I wonder how your model

355
00:14:22,880 --> 00:14:20,880
results compare against the data with

356
00:14:25,370 --> 00:14:22,890
hydrogen concentration thresholds

357
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because it used to be thought that the

358
00:14:30,050 --> 00:14:28,410
km was the control of how much what's

359
00:14:32,060 --> 00:14:30,060
the lowest concentration of hydrogen

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00:14:34,519 --> 00:14:32,070
solution these methanogens could grow on

361
00:14:37,250 --> 00:14:34,529
but later on it kind of seems like it

362
00:14:38,810 --> 00:14:37,260
panned out that it turns big it boils

363
00:14:40,760 --> 00:14:38,820
down to the bioenergetics of how much

364
00:14:43,310 --> 00:14:40,770
energy it takes to pump a single ion

365
00:14:46,130 --> 00:14:43,320
across the membrane three chemiosmosis

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00:14:48,260 --> 00:14:46,140
right so I was wondering have you mapped

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00:14:50,180 --> 00:14:48,270
that on to the hydrogen question two and

368
00:14:52,550 --> 00:14:50,190
if that could help you understand your

369
00:14:58,639 --> 00:14:52,560
results so that that threshold is that

370
00:15:01,160 --> 00:14:58,649
minus 10 kilojoules so I think what

371
00:15:03,650 --> 00:15:01,170
we've seen in environments that that

372
00:15:05,110 --> 00:15:03,660
energetic value is much much much more

373
00:15:06,759 --> 00:15:05,120
negative than that

374
00:15:09,310 --> 00:15:06,769
I guess I'm not understanding your

375
00:15:11,319 --> 00:15:09,320
question very well but we can talk about

376
00:15:13,449 --> 00:15:11,329
later psychic and how about the km

377
00:15:14,980 --> 00:15:13,459
whereas the km from is it from scientist

378
00:15:17,019 --> 00:15:14,990
a scientist at a chrome containing

379
00:15:19,750 --> 00:15:17,029
methanogens likes our sonali's or is it

380
00:15:20,800 --> 00:15:19,760
from like a mechanic a CODIS I don't

381
00:15:23,019 --> 00:15:20,810
remember okay

382
00:15:49,410 --> 00:15:23,029
but I have the paper if it'll check with

383
00:15:54,570 --> 00:15:52,350
thanks sorry thanks Sean let's take