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[Music]

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[Applause]

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I'm excited to be here and today I want

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to talk to you about Rubisco in marine

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environments and so you've had a little

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bit of introduction to risk oh and

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Rubisco is the enzyme that fixes carbon

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dioxide in photosynthesis so just to put

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it into context I have I'm gonna go

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straight to this slide this is a

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schematic of how photosynthesis works

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and you can see Rubisco up here this is

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the enzyme that takes co2 and fixes it

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into organic carbon and then it is used

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oxygen excited synthesis so all plants

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algae cyanobacteria all use this process

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here and you can see Rubisco is part of

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the light independent reaction and it

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gets the reductant and energy to power

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this light independent reaction by using

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this light dependent reaction which

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harnesses the sun's energy and uses

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chlorophyll and all that to generate to

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generate oxygen and so as I said all

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plants algae cyanobacteria use oxygen

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'ok further synthesis to autotrophic we

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fix carbon and this is by far and away

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the most dominant way of fixing carbon

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on our planet right now but there are

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parts of the earth which are there is no

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light parts of the early Earth where and

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different environments where oxygen 'ok

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photosynthesis wasn't around and there's

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actually plenty of bacteria and archaea

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at the moment that's also used Rubisco

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but they don't have this light dependent

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pathway they can use oxidized other

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chemicals and do other reactions to

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generate reductive and energy so I

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really want to focus on Rubisco because

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it is such an important part when you

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think about how carbon is fixed on our

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planet Rubisco is the main one that does

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that and I want to talk about it in the

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marine environment because half of all

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the photosynthesis on the planet happens

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in the oceans alright so that means that

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every second breath you take that oxygen

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was produced by algae in the oceans

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which is circle and in the oceans the

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oxygen 'ok photosynthesis is largely

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produced by is this group called

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phytoplankton which is a very loose term

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that covers all sorts of single-celled

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microbes that do oxygenic photosynthesis

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and they come from a remarkably diverse

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background all the way from

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cyanobacteria to sort of hetrick on

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switch

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diatoms oquawka livers that make these

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beautiful shells to the screen algae

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anyway it's just incredibly diverse they

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have all these different types of

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Rubisco compared to plants which all

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arise from one ancestor with you know

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one type of Rubisco so the diversity in

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the oceans is huge and then you go into

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the deep oceans and hydrothermal vents

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and anoxic zones and you have all the

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bacteria and archaea that are also using

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a Rubisco to fix co2 so if we want to

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understand how a Bisco has evolved and

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autotrophic carbon fixation has evolved

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on our planet the oceans is a great

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place to look and so Rubisco stands for

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regulation one five five phosphate

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carboxylase oxygenase and which is i'm

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getting very good at saying that it's an

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amazing enzyme right so I said 99% of

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all biologically fixed carbon is thought

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to go through this one enzyme they think

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it's ancient over three billion years

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old and you would think with over three

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billion years of evolution it would be

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very well adapted and good at what it

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does right now right but it's not

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it is terrible it is a terrible terrible

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enzyme it is really big it is really

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slow you need a high concentration of

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co2 around Rubisco for it to work and it

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is competitively inhibited by oxygen

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which is a challenge right in an

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oxygenated atmosphere and so the big

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question is why is this the enzyme of

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choice why is this how this planet fixes

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its carbon for life and so I want to

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introduce to you a couple of projects

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that my lab group is going through

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studying Rubisco in the diversity of

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Rubisco kinetics in modern species and

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well how that can help us inform this

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question and so I want to say that the

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one of the fundamental sort of the

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current consensus of why Rubisco isn't

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so much better than what each it is is

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because Rubisco is adapting it is

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evolving but it is biochemical

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biochemically constrained between how

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fast it can fix carbon and how specific

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it is for co2 and so what I'm showing

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you on the left-hand panel here is

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basically the speed of carboxylation

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which is the k-kat against its

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specificity for co2 / oxygen and you can

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see they generally fall across this line

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that the faster you can fix carbon the

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less specific you

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the co2 now the problem is as most of

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this data is based on plants because

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that's what people study it's really

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easy to go out and grab a plant these

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two outliers

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these are cyanobacteria all right and

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actually if we go into the marine

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environment and extract Rubisco is from

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a variety of different organisms and

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measure their abisco kinetics we see a

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remarkable diversity so that's the

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middle panel here and what I'm showing

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you on the y-axis is the KC this is the

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Hoff situation constant for co2 so the

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concentration of co2 you need to give

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half the maximum rate so a high scan

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means that you need a lot of co2 to

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saturate the enzyme a low km means it's

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very has a good affinity for co2 and

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then these are the values from bacteria

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diatoms which are really dominant

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phytoplankton group in the oceans and

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some red algae the plants and the

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cyanobacteria and you can see this

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variable response and I want to point

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out that this is a log scale on the

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y-axis alright so there's a truly

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dramatic range of Rubisco kinetics in

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these different organisms and if we take

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these diatoms which are dominant in the

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marine environment and plot their cans

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and carboxylation speeds on where we

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would expect them to fall so the grey is

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the expected relationship between

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carboxylation speed and affinity for co2

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and the diatoms are in black here and

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you can see they fall completely not on

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the line alright so we have a

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fundamental misunderstanding of how our

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Bisco works on our planet and the other

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thing is that these measurements are

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made at 25 degrees Celsius which is very

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relevant for plants they're not so

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so in the marine environment we get

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sorry don't need this out in the marine

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right you're gonna have to listen to it

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this is this is the GoPro going through

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the sea ice up in northern Alaska and I

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don't know if you can see it very well

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but this brown coloration on the bottom

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this is a metre and a half thick sea ice

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these are all diatoms growing within the

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bottom five centimetres of sea ice right

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it's an incredibly productive ecosystem

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it feeds everything out there these are

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microscopic organisms that just grow in

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these dense mats and this is at minus

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two degrees Celsius so we know that

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temperature has a big effect on how

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enzymes work and Rubisco is no exception

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and from what we can see extracting

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Rubisco from

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Paulo diet owns from warm species all

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these different things it doesn't look

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like Rubisco is cold-adapted which means

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Arco temperatures it slows down

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dramatically

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so in pink here I'm showing you the cup

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oxidation rate of which is on this axis

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here at 20 degrees and at 0 degrees

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Celsius and you get an Eightfold

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reduction of carbon fixation speed going

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from 20 to 0 degrees Celsius

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alright so it slows down a lot in

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addition the km the house situation

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constant goes from about 40 which don't

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on the it's in blue and it's shown on

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this axes here it goes from about 45

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down to 15 so it becomes more specific

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for co2 but it's really really slow and

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so polar diatoms at cold temperatures to

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compensate for the slow carboxylation

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rate they dramatically up regulate how

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much for Biscay they have and so this is

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a polar diatom species here grown in the

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lab could fragilaria up Cecil Andrus

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this is data from the field and

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Antarctica of a big diet on bloom at

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minus 2 degrees Celsius and they have

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about 16 percent of their total protein

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as Rubisco compared to only about 2.5

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percent at diatoms that grow at about 20

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degrees Celsius and this raises an

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interesting question on the theoretical

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how fast you can grow and fix carbon at

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cold temperatures because it's a

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combination of how fast the Rubisco

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enzyme works and then how much Rubisco

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can you actually make in your cell so it

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gives an interesting theoretical limit

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of how fast carbon can be fixed and so

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this work is being continued on I have

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two postdocs Ming Lee who's actually

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starting on Monday so we have all these

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Rubisco kinetic measurements over a

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range of temperatures he will be using

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membrane and mass spectrometry to

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measure carbon fixation of the whole

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cell over these different environments

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to try and get a good idea of wholesale

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carbon fixation rates and Rubisco

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kinetics and then Katrina Schmidt who

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she's not here today um but she is

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wandering around this week she is

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growing sea ice in the lab that we can

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grow algae in the sea ice so we get a

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lab environment that's much more

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representative of what we see out in the

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field so another project I want to talk

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about is looking at Rubisco

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fractionation so we just had a great

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talk on Delta C 13 and Rubisco

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fractionation

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and yes so a lot of the assumptions are

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that Rubisco fraction eights are 25 to

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29 per mil and once again this is based

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largely on literature on plants at 25

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degrees Celsius and so what I'm showing

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you here is a phylogenetic tree of all

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the different types of Rubisco that are

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found in different organisms I stole

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this tree from you cannot see probably

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but it's cushaw Bettles paper so these

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are the different types of Rubisco I've

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matched it up with in different

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organisms that have these different

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types of Rubisco and so plants all have

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this form 1b but in the marine

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environment we actually have most of

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them the eukaryotic phytoplankton have

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form C D right so a lot of diatoms cook

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ELISA floors have this seedy group and

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then there's cyanobacteria some have 1a

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so that won't be there's very few

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measurements that have been taken are

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the ones that have been measured and

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published I've shown on the right-hand

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panel here I want to reiterate I forgot

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to put the references up this is not my

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research this is a compilation of

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literature by a whole bunch of different

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people so if but I have the list so if

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anyone wants a specific number I can

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tell you who did the research and which

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paper it is but what's interesting is we

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only have three measurements from marine

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eukaryotic phytoplankton and they are

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hugely variable ie hooks as the value of

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11 per mil a diatom has 18 a red algae

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has 30 is this dramatic difference of

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Rubisco fractionation from these

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different types of old from film CD

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Rubisco so we need to look into this a

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little bit further so my grad student

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Susan who's in the audience is working

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on extracting Rubisco measuring the

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isotopic fractionation so if you have

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any questions definitely go talk to her

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and the last thing I want to talk about

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today is looking at Rubisco in even more

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extreme environments than in sea ice and

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so I want to go back to these cry pegs

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that Jody Deming was talking about and

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she already mentioned that we found

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Rubisco in there so you've stolen might

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my story but yeah it's for these cry

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fakes are truly amazing environments

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right they are ancient marine sediments

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for those that went here for Jody's

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chocolate I think most people were they

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are ancient marine sediments trapped

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within the permafrost today are really

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cold about minus 8 degrees Celsius that

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they're anoxic there anywhere between 14

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to 40,000 years old right and they are

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filled with bacteria they are filled

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with organic carbons so the vast

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majority of the bacteria in there are

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heterotrophs but we wanted to see if

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there were Rubisco and so once again

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this work was done by JC who is JD

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Demmings postdoc these are metagenomic

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samples from different car i peg samples

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that they took and these are Rubisco

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genes and their associated bacteria up

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here so we see this wide diversity

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they're not in high abundance these

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genes but they're definitely present in

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the Crytek's carbon fixation is

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happening and one bug I wanted to pull

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out in particular because this one kept

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coming up is this gamma proteobacteria

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could thio microsphere arctic air which

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I stole this picture from this paper

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it's an obligate camo letter autotroph

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it's sulfur oxidizing it has two Rubisco

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so it has a form one and a form two now

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lots of prettier bacteria can have two

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different types of Rubisco but generally

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the form one is expressed under oxic

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environments the form two is expressed

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under anoxic environments because they

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have different kinetics why this guy in

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this very stable ancient environment is

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keeping these two Rubisco 'he's might be

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a really cool thing to look at to

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understand how gene evolution works in

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these extreme environments so just to

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round it up yeah 99% of all biologically

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fixed carbon goes through Rubisco is

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this amazing ancient enzyme and by

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studying the kinetics the adaptation the

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evolution the diversity of Rubisco in

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all these different organisms and

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environments in the modern planet we can

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get a really good idea of trying to

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reconstruct how evolution adaptation

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autotrophic carbon fixation has evolved

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on the planet and just to say thank you

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obviously this work was a big

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compilation of lots of people so hannah

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dawson actually is my grad student she

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gave a talk yesterday on sea ice algal

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metabolism using metabolomics we have

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Susan and Catrin the Deming lab group

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and these are my funding bodies so yeah

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thank you very much and I'll take any

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Thank You Jody oh maybe one quick

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and Tony Murray from Georgia Tech so you

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said that there's a bunch that sort of

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lie on this nice trade-off line between

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speed and the specificity and whatnot

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but there's these others that don't and

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then you mentioned that temperature

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changes the numbers are thing that maybe

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ones that don't follow a nice trade-off

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might either because might be trading

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off with something else like I'm not

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necessarily temperature but something

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else but another dimension that like

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that like maybe the trade offline is

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just a slice of a trade off plane or

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something like that yeah no it's a good

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question I think there's obviously a lot

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more complexity there that we don't

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fully understand yet the trade offline I

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showed you all those that was all

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measurements taken at 25 degrees Celsius

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so all those ones were like the standard

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when you measure a biscuit kinetics it's

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25 so you can compare everything yeah

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but yeah obviously they don't function

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at 25 degrees Celsius all of them and so

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they've evolved to different co2

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environments to different temperatures

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different salinities all sorts of pH you

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know there's a whole myriad of different

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things we could look at and it hasn't

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really been explored yet so that's