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[Music]

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[Applause]

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so I'm going to try to wrap up the

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session quickly so we can all get to

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lunch but Laurie and Pete both did a

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great job of explaining by

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electrochemical systems and they're

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especially the relevance to astrobiology

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and I'll talk about one of our systems

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so first I'd like to acknowledge my lab

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group I'm a postdoc at the Naval

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Research Lab Sara Glavine is my PI Bryan

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Eddie and Anthony Malinowski help with

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bioinformatics and Matt Yates and Lonnie

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tender are electro chemists and so

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there's a lot of us that have come

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together to characterize the system I'll

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talk to you about today and so again we

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heard from both Lori and Pete about bio

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electrochemical systems and I really

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like what Pete had to say that all life

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is sort of a bio electrochemical system

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in the environment but again we're

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looking at bio electrochemical systems

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basically as a way to culture organisms

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or communities and we can look directly

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at electron transfer and see what energy

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is required and what energy is moving

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through the system and so here I have a

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benthic microbial fuel cell which is

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benthic is at the bottom of the ocean or

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a river and typically we have one

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electrode that's in the sediment and at

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this electrode micro rna's

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microorganisms are capable of oxidizing

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organics and those electrons are moved

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pushed onto that electrode the electrons

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can move through the system to another

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electrode in the overlying seawater and

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here other microorganisms are capable of

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use utilizing those electrons for

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reduction reactions and so there's

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generally two types of BES where you

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keep either an electrode at an anodic

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potential and you have electricity

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production or you keep the electrode at

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a cathodic potential and you use the

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microorganisms use that those electrons

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for reduction reactions and so again as

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Pete and Laurie showed us there's many

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applications of BES with relevance to

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astrobiology specifically if we want to

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look at how electron transfer is working

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in unique communities and so Laurie

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showed some hydrothermal vents there's

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also some applications of microbial fuel

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cells to life detection in this case

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current production would be correlated

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with photo or chemo with autotrophic

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microorganisms BES in general have a lot

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of use in wastewater treatment nutrient

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recycling and so they're also looked at

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as potential life support systems for

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both the ISS and for long-term space

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travel and so the system I'm going to

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talk to you about today is a unique

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system where we were trying to make a

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rechargeable battery so many my

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microbial electrochemical systems can be

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thought of as batteries as Laurie barge

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mentioned but what we wanted to do here

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instead of having a set anode and a set

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cathode in the ocean sediment and in the

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overlying sea water and having power

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production from oxidation of organics at

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the anode we wanted to see if we could

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basically switch this anode to a cathode

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and push power into the system we wanted

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to be able to push power into the

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sediment have organisms utilize those

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electrons and store that charge in

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charge carrying molecules in the

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sediment we'd be able to use this later

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fueling instruments at the bottom of the

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ocean or submersibles for example and so

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what we did is we took an initial

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inoculum from a river sediment and we

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put it we brought it into a lab scale

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environment and we used a typical

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age cell by electrochemical reactor and

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so here we don't have a sediment

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electrode but we have a counter

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electrode and a working electrode the

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working electrode is the one that we're

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going to switch the potential back and

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forth to see if we can both produce

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power and consume power depending on our

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needs and so our NOC um was a river

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sediment we used anaerobic artificial

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seawater as a culture medium and the

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working electrode was a piece of carbon

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cloth and basically we alternated the

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the potential of this working electrode

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from operating at a cathode where

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electrons are available to the

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microorganisms to operating as an anode

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where the electrode operates as an

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electron acceptor we did oopsie we used

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a twenty-minute charge/discharge cycle

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and so every 10 minutes the electrode

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potential would switch on the working

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electrode we also covered the reactors

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so that we could harvest or enrich for

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non photosynthetic organisms and so on

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this graph on the right its current

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density over time and basically at bolt

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when the electrode is operating at

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either potential a current is generated

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and as you can see around 10 days we

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start to see this symmetric increase and

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decrease in current and each data point

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is representative of 1 10 minute cycle

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and so every 10 minutes again this cycle

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is switching between a notic current and

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cathodic current and so this symmetric

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increase in both currents suggests that

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the same pathway or biochemical reaction

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is occurring to allow this reversibility

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of the system so what we wanted to

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figure out who's there and what are they

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doing we initially inoculated from a

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river sediment and so it's just a

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bacterial community that's been enriched

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for this reversibility so we did first a

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met a genomics analysis we retrieved

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initially 135 bins which could be

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potentially 135 different organisms only

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58 or those bins have at least 80%

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completeness

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there's at least 16 bins that are make

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up at least 1% relative abundance in the

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community and 10 of these bins are at

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least 92% complete 5 bins have at least

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relative have a relative abundance at

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least 6% and of these 5 2 bins are Delta

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proteobacteria and so for a bes this

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indicates relatively high diversity and

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the presence of sulfate-reducing

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bacteria and so in our metagenomics

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analysis we were also able to assign a

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taxonomy these are our what we're

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confident in assigning but you'll see

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that our average abundant our most

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abundant organisms about 22% abundant

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sorry across the 6 replicates and this

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maps to a sulfate-reducing the solver

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Occulus bar CI the next eight bins

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account for about 66 percent of the

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total abundance of the community and

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you'll also notice that i included two

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bins with very low abundance but you'll

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see that we have another sulfate reducer

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and two other possible sulfate reducers

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and so now if we switch to the activity

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looking at our meta transcriptomics the

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reason I included those two very low

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abundant been low abundance bins is

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because bin 127 is actually our most

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active bin and so this maps to the

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sulfur over bo alkali Phyllis and so it

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appears that we have some sulfate

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reducing organisms at work in the

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reversible system and so I'm gonna focus

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on our two most abundant and the most

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active organisms again we have the self

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Arceus bar CI which is the most abundant

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it's a sulfate reducer amezo file and

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has been shown to oxidize for me in

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acetate to carbon dioxide via the wood

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long dull pathway our most active

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organism is also our most interesting

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organism so it's technically classified

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as a sulfate reducer but in pure culture

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in the lab

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it has been shown to oxidize sulfide

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with a high expression of sulfate

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reduction genes so this organism

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actually doesn't have any genes for

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sulphide oxidation but in culture it

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oxidizes sulphide via possibly the

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sulfate reduction pathway

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it also has genes for carbon fixation

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and it has been associated with an anode

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in a sulfide oxidizing by

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electrochemical system and so we wanted

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to look at what genes were

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differentially expressed between our two

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different potentials so when the

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electrodes operating as an anode versus

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when is operating as a cathode and

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basically I highlighted in red that the

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most highly expressed genes are a bunch

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of hetero disulfide reductases these

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were initially characterized in

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methanogens but in bacteria they're

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considered to replace the reverse

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dissimilatory sulfite reductase genes

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and so these genes are down regulated at

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a cathode and now we can sort of start

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thinking about what metabolism is

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occurring in our system but first we

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wanted to look at what genes were highly

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expressed at both conditions and so

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these genes were highly expressed both

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at an anode or at cathodic potential and

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we have the complete genes pathway for

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sulfate reduction and these genes are

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also actually correlated with our most

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active organism the sulfur Vibrio alkali

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Phyllis and so if we put all this

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together including looking through the

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literature at pure cultures of alkali

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Phylis what we think is happening is

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that when the electrode is operating as

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a cathode this is offering electrons to

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the microorganisms and we believe that

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sulfate reduction is taking place

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through the normal sulfate reduction

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pathway for which all of the genes are

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highly expressed however a tan

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we believe that sulphide oxidation is

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occurring again from our same highly

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active organism but through a proposed

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reversal of the normal sulfate reduction

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pathway and Thora pat all are the ones

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that had seen this sulfate reducer

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performing sulphide oxidation with high

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expression of the sulfate reduction

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genes and they proposed a new pathway

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for sulphide oxidation that is simply a

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reverse of the sulfite of the sulfate

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reduction pathway and so again since we

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also see our main or our main active

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organism at the anode of be ESS in other

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systems this is our current hypothesis

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and so to bring this back to

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astrobiology throughout the week we've

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heard a lot about following the energy

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sources and also a lot about what we

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don't know and so on as Laurie and Pete

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mentioned I think BES are a great way to

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culture either pure pure pure cultures

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of organisms or communities and look

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directly at electron transfer and what

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energy sources are required for those

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kinds of events and so I'll leave you

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with this slide and I'll take any

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questions if we have time or you can

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catch me on your way to lunch Thanks

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I have two questions the first did these

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reversible oxidation reduction occur

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equally in the light and the dark and

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then the second question would be

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relating back to the previous speaker in

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a comment you made how much how much can

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you store for future use and are you

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talking about the sea floor fervor for

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submersibles how it how would that

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affect the surrounding ecology of the

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sea floor so for the first question I

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don't we haven't looked at light versus

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dark we've just been looking at

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non-photosynthetic communities so i

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can't i'm unfortunately i can't answer

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that question but for the second

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question so were our initial goal was to

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try to create a localized fuel source in

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the sediment because what is often

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limiting at that point is mass transport

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of the organics to you know and

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oxidation to the electrode and so if we

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have a localized fuel source by the

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electrode where we can store these

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discharge it would be available later in

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data I haven't shown we've tried to

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increase the times time of the cycle so

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this here was just a 10 minute cycle

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back and forth we've gone up to 12 hours

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and the bacteria do not like that so we

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tried to mimic a diurnal cycle and

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basically it resulted in bacterial death

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that current was not produced and so

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this this system isn't actually in a

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river or ocean sediment we do have other

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actual systems that are in ocean

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sediment but I don't know the specific

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parameters of the that current

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generation or what their what they see

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at them but Lenny Tender is one of my

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co-authors and he has systems actually

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okay well thank you all for staying and

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have a nice lunch