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[Music]

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okay so we're gonna shift gears a little

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bit here and so my project largely

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focuses on the evolution of

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multicellularity uh in bacteria

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specifically so titled here cellular

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differentiation within an obligate

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multicellular bacteria

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so where I like to start is just

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generally when we think about the

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evolution of life on Earth we can kind

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of think of it as an increase in

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complexity as as life continue to evolve

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and this is yes and over Simplicity but

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thinking of it as molecules coming

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together to form a first cell and

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eventually getting a multi-cellular

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organism and then some something that

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looks like the life that we have on

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Earth today

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if we look at our classic uh Tree of

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Life where we have different domains of

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the bacteria the archaea and the

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eukaryotes generally we tend to think of

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all the multicellular life forms

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belonging to the Eukarya and we think of

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the bacteria and archaea as these simple

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um if we look at uh the Tree of Life as

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we know it today uh multicellularity

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actually it can be plotted across the

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entire uh tree of life and so what I'm

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showing here is the aggregative uh

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evolution of multicellularity or a

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clonal uh evolution of multicellularity

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and we see it present in the bacteria

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the archaea and the Eukarya of course

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and so just focusing in on some bacteria

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that are capable of this these are just

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some micrographs showing different uh

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cyanobacteria that are in those chains

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up there in the upper left and then mixo

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Cox mixobacteria that sporolate an

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archaea called methanosarcina another

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example is this uh bacteria called cable

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bacteria that form these long centimeter

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long filaments and can actually move

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electrons along that

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so the organism that I study is called

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multicellular magnetotactic bacteria or

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MMB for short because I just don't want

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to say that the whole talk and so this

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is what they look like where we have a

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tem image sewing uh where these cells

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are grouped together in this kind of

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soccer ball shape or football shape

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um and then here in the lower half just

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an sem showing you what that structure

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looks like so I built a cartoon kind of

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showing

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um what this Ultra structure looks like

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and one of the things I want to point

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out that pertains the name is this

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magnetotaxis and so they make these uh

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organelles inside the cells called

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magnetosomes where they synthesize a

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Paramount or ferromagnetic mineral that

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allows them to sense Earth's geomagnetic

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poles and then they can taxi in the

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water column or the sediment column

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um they also have these carbon or energy

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storage granules inside them this

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acellular Center so it's just one layer

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of cells surrounding this acellular

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Center

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and then these actin like filaments that

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seem to have some something to do with

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um I've referred to them as obligate

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multicellular organisms and this is rare

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in bacteria in fact the only example

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where the hypothesized life cycle is

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that they grow in size and then the

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entire consortia divides and so we don't

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typically see this in uh bacteria where

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typically we see this this facultative

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multicellularity so they can be uh

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multicellular but they can also exist as

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a single cell and that's true for all

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the examples I showed you with the tree

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life

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so here's just an image of uh one of the

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MMB from my sample site and kind of what

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we think it looks like uh MMB dividing

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into possibly three

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I also mentioned moment of truth if the

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video works

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um that they're magnetactic oh let me

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see if I can get this to work

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Okay cool so what we have here is a uh

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tube with the MMB in the bottom of it

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and then a magnetic stir bar next to it

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and if you just watch it you can see

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them swim up out of the bottom of that

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tube and they taxi towards the the stir

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bar these ones are going towards the

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magnetic north

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here in on the right is a hanging water

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droplet just on a cover slip and there's

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a magnet uh to the right and then what

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I've done is just move that magnet turns

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around they start taxiing the in the

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opposite direction

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so that's uh just showing their

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magnetotaxis

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um it helps when we think of

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multicellularity to have some criteria

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for what that is

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and so just a list of these would be

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built from several cells of the same

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species a specific shape and

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organization and synchronized growth so

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that exclude things like cancer

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no competition between the cells

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coordinated behavior in response to

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external or internal stimuli existence

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of cell to cell signaling and then this

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last one that's kind of like the

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catch-all metabolic differentiation or a

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division of labor so with my organism

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they fit these first four and these

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second the last two are what we're kind

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of looking into

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um one of the things we found with our

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project was that the these MMB are not

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actually clonal and how we did this was

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we sorted whole consortia's

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did multiple displacement amplifications

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so we Amplified their entire genome and

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sequenced that and we were able to map

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reads to the longest read the best

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assembly there and look at these single

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nucleotide polymorphism differences

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and what we found was that they have

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compared to controls which is a

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pseudomonas control as well as other

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environmental cosorts they have this

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much higher

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um single nucleotide polymorphism rate

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than than what we see with other

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organisms which was kind of a surprise

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and we're still scratching our heads

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about this

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um and that equates to 20 to 100

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nucleotide polymorphisms in the genome

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and their genomes are about eight

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megabases which is about double that of

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E coli

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another thing that we looked into was

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this metabolic differentiation or this

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division of labor and this was done by

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doing stable isotope incubations where

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we incubated them in the presence of

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these 13c or deuterium oxide

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chemicals and then we use uh

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nanosecondary ion Mass spectroscopy to

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look at those and map that back where we

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found in the lower left whereas the 13c

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image differences in the use of that

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substrate indicating this the vision of

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Labor that we suspected

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so with that just to kind of give

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conclusions and takeaways

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um the m and b are the only known

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obligate multidocellular bacteria that

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we know of yet

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um they are not clonal and do not

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conform to these canonical ideas of what

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multicellular multicellularity is where

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we typically have this clonal

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development

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from where one cell divides into

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daughter cells that stick together or

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this aggregative multicellularity and

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they seem to

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fall somewhere in the middle there

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they also engage in a division of labor

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as we were looking at with the metabolic

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differentiation

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and then of course just to think the lab

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and all the collaborators that help us

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with that thank you

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[Applause]