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[Music]

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[Applause]

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thank you for the opportunity of

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speaking today and thank you all for

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being here so I'm going to go back in

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time hmm and focus this time on Mike

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microbial communities in iron rich

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oceans at the onset of the great

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oxidation event so the early Earth has

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been habitable ever since essentially

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the beginnings of its origins this is

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just a simplified diagram of some

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periods in time just to show that even

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though the earth has been inhabited ever

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since we've known of the existence of

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life four billion years ago different

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environments existed in which different

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the habitability was probably not the

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same for different species of

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microorganisms for example the origins

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of life Earth was an anoxic world with

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an anoxic atmosphere and iron rich

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oceans in which the majority of the

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metabolisms were anaerobic around the

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genomic record and fossil record tells

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us that cyanobacteria were able to begin

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to produce oxygen from water and around

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3 billion years ago if not earlier and

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even though they were able to produce

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oxygen for a long time for half a

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billion years two billion years oxygen

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was being produced but it did not

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accumulate in the atmosphere but at some

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point around 2.4 billion years ago

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oxygen production began to ramp up and

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very rapidly oxidized the globe perhaps

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not the modern countries of oxygen but

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enough to change the metabolic rules of

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the planet from an Arabic driven to a

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mostly anaerobic driven to mostly

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aerobic driven and now than in modern

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earth we met the majority of the biomass

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on earth is as an aerobic metabolism and

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at the same time well oxygen was

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produced and I'm sure you've recognized

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this not from previous talks iron

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concentrations decrease dramatically so

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what I'm interested is in understanding

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what was the microbial factors and the

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forces that shaped this period of time

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of cryptic oxygen cycling

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and what made it this ramped up the soul

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so rapidly so in order to dig a little

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bit deeper into these one of the focuses

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that one of the mythologies that I'm

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interested is the the reactivity of

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oxygen in a four genus ocean so to come

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up with optogenetic photosynthesis or to

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produce oxygen in a virginal environment

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is not really a good idea because oxygen

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not only will react with cellular

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components DNA proteins and lipids and

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as being especially detrimental in an

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anaerobic world where metabolisms are

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have enzymes that our oxygen sensitive

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but under high iron conditions you have

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that Fenton type of chemistry which

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accelerates iron toxicity on top of that

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iron gets oxidized by oxygen producing

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solid iron 3 which can also in

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crustacean and and be another reason for

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toxicity but there's a problem with this

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scenario so in this scenario it is

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proposed that cyanobacteria would have

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had a hard time to overcome iron

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toxicity and this could have delayed the

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oxygenation of earth and there's a very

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important piece missing though and which

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is what I want to focus on which is

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other other species other microbes so

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around 2.4 billion years ago which I am

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circled here in yellow there were

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already many ancestral lineage is

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present and diverged

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for example the ancestors of Delta

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fertile bacteria the under gammas and

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betas and Terra bacterial ancestors were

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already likely coexisting at that time

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and that means increased number of genes

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and functionalities and potentially

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mechanisms to cooperate together

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particularly important could have been

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proteobacteria many of the

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Proteobacteria that we know today are

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experts in cycling metals both iron

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oxidation and iron reduction so if you

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include a metal reducer in this scenario

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you can have many protective effects by

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the reduction of oxygen or the reduction

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of iron 3 preventing incrustation so in

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order to understand this

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potential scenario a little bit better

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one can study potential early earth

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analogs on earth the problem with that

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is that they could be very complex you

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even though they're more realistic and

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also what I wanted to do is come up with

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an experimental setting to simplify the

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conditions and also simplify the number

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of individuals to control the parameters

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better and understand the mechanisms

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that could have been involved in these

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interactions another problem with this

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setting the previous scenarios that

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there are no modern analogs it's really

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hard to find a serve an illuminated

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surface in on earth that has an anoxic

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atmosphere so what I did is I built a

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semi high throughput pre goe consortium

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to explore cooperation on earth by in an

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anaerobic chamber so I used to model

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organisms cyanobacteria see no Coco's

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BCC 7002 and strains of Salmonella the

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Shannara genus which are metal producers

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used use them either alone or together

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in pairs in an anoxic atmosphere and

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oxygen was allowed to be produced from

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photosynthesis but it was allowed to

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diffuse into the anaerobic chamber so

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this is conducted these experiments into

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in in 10 milliliter volumes inside 20

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milliliter wells culture plates so

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oxygen would diffuse into a 300 liter

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chamber mimicking the anoxic

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environments and the treatments were

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different concentrations of iron - so as

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expected like previous work had shown

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cyanobacteria as iron concentration

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increased to 1 millimolar

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lost their ability to grow and it has

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previously been shown that it's due to

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iron toxicity already at 500 a they were

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showing a lag in their growth and here

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I'm showing growth of cyanobacteria in

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the presence of different strains of

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Salmonella species and as you can see

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the reverse happens as iron increases in

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the presence of Salmonella most

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cyanobacteria

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speech I mean this one species but in

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all these different experiments I know

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Vettori is able to grow and the growth

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is restored annoying Salmonella and in

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the same culture under higher iron

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concentrations the growth is favored too

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so there's a relationship between the

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high amount of iron and the yields and

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growth rates of Shanina and

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cyanobacteria when they're growing

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together so when I went and measured

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iron concentrations iron ii

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concentrations with the cyanobacteria

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alone in both higher and 501 millimolar

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iron ii concentrations in the iron

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levels immediately decreased in the

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first few days but which human ella the

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iron levels remained essentially stable

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which means that there was not enough

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oxygen to oxidize iron probably consumed

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by shewanella

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or iron could have been reduced but in

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any case the mechanisms of protection

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were related to the availability of

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oxygen and iron so among all the

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different strains tested shewanella

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baltica and shewanella alga were the two

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that yielded the yield similar under

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high iron or low iron conditions so to

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understand potential reason for this I

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incubated each shinola independently on

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its own under different concentrations

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of hydrogen peroxide meaning different

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concentrations of hydro peroxide stress

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and so the better helpers the ones that

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were able to get cynical Coco's to grow

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almost like no iron in Noren conditions

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they were able to resist hydrogen

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peroxide better so ro s stress better

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than the poor poorer helper so bringing

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everything all these different lines of

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evidence together you can I conclude

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that iron concentration will impact the

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interactions between the Proteobacteria

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and cyanobacteria and this could have

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driven the community structure in

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ferruginous and early oceans

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cyanobacteria Fitness also increased

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when there was a metal reducing partner

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so it suggests that the habit of

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habitability arranged in a community

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change depending on the community

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composition in a given environment so

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this would be important too for future

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habitability tests whether there's one

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species or more will likely change the

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the results also cyanobacteria

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benefitted by coin inhabiting with

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shewanella only at higher iron

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concentration so and again suggesting

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that partnerships that may have been

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important during the Proterozoic or late

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Archaean may be very different than

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those found in modern environments so

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again analog choice versus experimental

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setup can yield different results and

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important to consider and also a cryptic

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oxygen cycle would have been sustained

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under high iron oceans by cyanobacteria

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and protocol partners which would

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explain why this would be another

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biological factor instead of abiotic

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reasons why oxygen would have persisted

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at low concentrations red cryptic levels

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without accumulating at the atmosphere

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so the end of the results and I would

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like to thank Jen lassen Chris Reinhard

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for their support during these MPP

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postdoc experience things to NASA for

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allowing me to carry out this research

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on the amazing people at the glass lab

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on the astrobiology community at Georgia

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Tech have you looked at the formation of

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colloids for example maybe iron 3 could

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form a chloride and maybe other elements

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a nitrogen cycle cycling you know

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different oxidation states of another

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element that might go through iron to

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iron 3 so I I put ammonium as a nitrogen

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source of nitrate which is a typical

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component of cyanobacteria media but I

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didn't look at that but that may be

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interesting to see whether reactive

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species could also be produced by that

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please come to my i dial psycho so I did

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not take points that would be I was

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thinking about doing that on a future

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experiment I was I'm going to select one

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of these shewanella species and then get

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more resolution and more resolved type

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of growth curve to see if there are

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changes between the iron and the oxygen

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levels over day and night cycles this

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was more like a high-throughput to see

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the range because even though they're

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also on another all metal reducers they

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do not have the same effect on the sign

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of a true growth which is also means

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that there's it's not a biomass issue

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there's other biological components in