This deep-sea mystery is changing our understanding of life

How deep into the Earth can we go and still find life? Marine microbiologist Karen Lloyd introduces us to deep-subsurface microbes: tiny organisms that live buried meters deep in ocean mud and have been on Earth since way before animals. Learn more about these mysterious microbes, which refuse to grow in the lab and seem to have a fundamentally different relationship with time and energy than we do.

I'm an ocean microbiologist
at the University of Tennessee,

and I want to tell you guys
about some microbes

that are so strange and wonderful

that they're challenging our assumptions
about what life is like on Earth.

So I have a question.

Please raise your hand
if you've ever thought it would be cool

to go to the bottom
of the ocean in a submarine?

Yes.

Most of you, because
the oceans are so cool.

Alright, now -- please raise your hand

if the reason you raised your hand
to go to the bottom of the ocean

is because it would get you
a little bit closer

to that exciting mud that's down there.

(Laughter)

Nobody.

I'm the only one in this room.

Well, I think about this all the time.

I spend most of my waking hours

trying to determine
how deep we can go into the Earth

and still find something,
anything, that's alive,

because we still don't know
the answer to this very basic question

about life on Earth.

So in the 1980s, a scientist
named John Parkes, in the UK,

was similarly obsessed,

and he came up with a crazy idea.

He believed that there was a vast,
deep, and living microbial biosphere

underneath all the world's oceans

that extends hundreds of meters
into the seafloor,

which is cool,

but the only problem
is that nobody believed him,

and the reason that nobody believed him

is that ocean sediments
may be the most boring place on Earth.

(Laughter)

There's no sunlight, there's no oxygen,

and perhaps worst of all,

there's no fresh food deliveries
for literally millions of years.

You don't have to have a PhD in biology

to know that that is a bad place
to go looking for life.

(Laughter)

But in 2002, [Steven D'Hondt] had
convinced enough people

that he was on to something
that he actually got an expedition

on this drillship,
called the JOIDES Resolution.

And he ran it along with
Bo Barker Jørgensen of Denmark.

And so they were finally able to get

good pristine deep subsurface samples

some really without contamination
from surface microbes.

This drill ship is capable of drilling
thousands of meters underneath the ocean,

and the mud comes up in sequential cores,
one after the other --

long, long cores that look like this.

This is being carried by scientists
such as myself who go on these ships,

and we process the cores on the ships
and then we send them home

to our home laboratories
for further study.

So when John and his colleagues

got these first precious
deep-sea pristine samples,

they put them under the microscope,

and they saw images
that looked pretty much like this,

which is actually taken
from a more recent expedition

by my PhD student, Joy Buongiorno.

You can see the hazy stuff
in the background.

That's mud. That's deep-sea ocean mud,

and the bright green dots
stained with the green fluorescent dye

are real, living microbes.

Now I've got to tell you
something really tragic about microbes.

They all look the same under a microscope,

I mean, to a first approximation.

You can take the most fascinating
organisms in the world,

like a microbe that literally
breathes uranium,

and another one that makes rocket fuel,

mix them up with some ocean mud,

put them underneath a microscope,

and they're just little dots.

It's really annoying.

So we can't use their looks
to tell them apart.

We have to use DNA, like a fingerprint,

to say who is who.

And I'll teach you guys
how to do it right now.

So I made up some data, and I'm going
to show you some data that are not real.

This is to illustrate
what it would look like

if a bunch of species
were not related to each other at all.

So you can see each species

has a list of combinations
of A, G, C and T,

which are the four sub-units of DNA,

sort of randomly jumbled,
and nothing looks like anything else,

and these species
are totally unrelated to each other.

But this is what real DNA looks like,

from a gene that these species
happen to share.

Everything lines up nearly perfectly.

The chances of getting
so many of those vertical columns

where every species has a C
or every species has a T,

by random chance, are infinitesimal.

So we know that all those species
had to have had a common ancestor.

They're all relatives of each other.

So now I'll tell you who they are.

The top two are us and chimpanzees,

which y'all already knew were related,
because, I mean, obviously.

(Laughter)

But we're also related to things
that we don't look like,

like pine trees and Giardia,
which is that gastrointestinal disease

you can get if you don't filter
your water while you're hiking.

We're also related to bacteria
like E. coli and Clostridium difficile,

which is a horrible, opportunistic
pathogen that kills lots of people.

But there's of course good microbes too,
like Dehalococcoides ethenogenes,

which cleans up
our industrial waste for us.

So if I take these DNA sequences,

and then I use them, the similarities
and differences between them,

to make a family tree for all of us

so you can see who is closely related,

then this is what it looks like.

So you can see clearly, at a glance,

that things like us and Giardia
and bunnies and pine trees

are all, like, siblings,

and then the bacteria
are like our ancient cousins.

But we're kin to every
living thing on Earth.

So in my job, on a daily basis,

I get to produce scientific evidence
against existential loneliness.

So when we got these first DNA sequences,

from the first cruise, of pristine samples
from the deep subsurface,

we wanted to know where they were.

So the first thing that we discovered
is that they were not aliens,

because we could get their DNA to line up
with everything else on Earth.

But now check out where they go
on our tree of life.

The first thing you'll notice
is that there's a lot of them.

It wasn't just one little species

that managed to live
in this horrible place.

It's kind of a lot of things.

And the second thing that you'll notice,

hopefully, is that they're not
like anything we've ever seen before.

They are as different from each other

as they are from anything
that we've known before

as we are from pine trees.

So John Parkes was completely correct.

He, and we, had discovered
a completely new and highly diverse

microbial ecosystem on Earth

that no one even knew existed
before the 1980s.

So now we were on a roll.

The next step was to grow
these exotic species in a petri dish

so that we could
do real experiments on them

like microbiologists are supposed to do.

But no matter what we fed them,

they refused to grow.

Even now, 15 years
and many expeditions later,

no human has ever gotten a single one
of these exotic deep subsurface microbes

to grow in a petri dish.

And it's not for lack of trying.

That may sound disappointing,

but I actually find it exhilarating,

because it means there are so many
tantalizing unknowns to work on.

Like, my colleagues and I got
what we thought was a really great idea.

We were going to read their genes
like a recipe book,

find out what it was they wanted to eat
and put it in their petri dishes,

and then they would grow and be happy.

But when we looked at their genes,

it turns out that what they wanted to eat
was the food we were already feeding them.

So that was a total wash.

There was something else
that they wanted in their petri dishes

that we were just not giving them.

So by combining measurements
from many different places

around the world,

my colleagues at the University
of Southern California,

Doug LaRowe and Jan Amend,

were able to calculate that each one
of these deep-sea microbial cells

requires only one zeptowatt of power,

and before you get your phones out,
a zepto is 10 to the minus 21,

because I know I would want
to look that up.

Humans, on the other hand,

require about 100 watts of power.

So 100 watts is basically
if you take a pineapple

and drop it from about waist height
to the ground 881,632 times a day.

If you did that
and then linked it up to a turbine,

that would create enough power
to make me happen for a day.

A zeptowatt, if you put it
in similar terms,

is if you take just one grain of salt

and then you imagine
a tiny, tiny, little ball

that is one thousandth of the mass
of that one grain of salt

and then you drop it one nanometer,

which is a hundred times smaller
than the wavelength of visible light,

once per day.

That's all it takes
to make these microbes live.

That's less energy than we ever thought
would be capable of supporting life,

but somehow, amazingly, beautifully,

it's enough.

So if these deep-subsurface microbes

have a very different relationship
with energy than we previously thought,

then it follows that they'll have to have

a different relationship
with time as well,

because when you live
on such tiny energy gradients,

rapid growth is impossible.

If these things wanted
to colonize our throats and make us sick,

they would get muscled out
by fast-growing streptococcus

before they could even
initiate cell division.

So that's why we never
find them in our throats.

Perhaps the fact that the deep
subsurface is so boring

is actually an asset to these microbes.

They never get washed out by a storm.

They never get overgrown by weeds.

All they have to do is exist.

Maybe that thing that we were missing
in our petri dishes

was not food at all.

Maybe it wasn't a chemical.

Maybe the thing that they really want,

the nutrient that they want, is time.

But time is the one thing
that I'll never be able to give them.

So even if I have a cell culture
that I pass to my PhD students,

who pass it to their
PhD students, and so on,

we'd have to do that
for thousands of years

in order to mimic the exact conditions
of the deep subsurface,

all without growing any contaminants.

It's just not possible.

But maybe in a way we already have
grown them in our petri dishes.

Maybe they looked at all that food
we offered them and said,

"Thanks, I'm going to speed up so much

that I'm going to make
a new cell next century.

Ugh.

(Laughter)

So why is it that the rest
of biology moves so fast?

Why does a cell die after a day

and a human dies
after only a hundred years?

These seem like really
arbitrarily short limits

when you think about the total amount
of time in the universe.

But these are not arbitrary limits.

They're dictated by one simple thing,

and that thing is the Sun.

Once life figured out how to harness
the energy of the Sun

through photosynthesis,

we all had to speed up
and get on day and night cycles.

In that way, the Sun gave us
both a reason to be fast

and the fuel to do it.

You can view most of life on Earth
like a circulatory system,

and the Sun is our beating heart.

But the deep subsurface
is like a circulatory system

that's completely
disconnected from the Sun.

It's instead being driven
by long, slow geological rhythms.

There's currently no theoretical limit
on the lifespan of one single cell.

As long as there is at least
a tiny energy gradient to exploit,

theoretically, a single cell could live

for hundreds of thousands
of years or more,

simply by replacing
broken parts over time.

To ask a microbe that lives like that
to grow in our petri dishes

is to ask them to adapt to our frenetic,
Sun-centric, fast way of living,

and maybe they've got
better things to do than that.

(Laughter)

Imagine if we could figure out
how they managed to do this.

What if it involves some cool,
ultra-stable compounds

that we could use
to increase the shelf life

in biomedical or industrial applications?

Or maybe if we figure out
the mechanism that they use

to grow so extraordinarily slowly,

we could mimic it in cancer cells
and slow runaway cell division.

I don't know.

I mean, honestly, that is all speculation,

but the only thing I know for certain

is that there are
a hundred billion billion billlion

living microbial cells

underlying all the world's oceans.

That's 200 times more than the total
biomass of humans on this planet.

And those microbes have
a fundamentally different relationship

with time and energy than we do.

What seems like a day to them

might be a thousand years to us.

They don't care about the Sun,

and they don't care about growing fast,

and they probably don't give a damn
about my petri dishes ...

(Laughter)

but if we can continue to find
creative ways to study them,

then maybe we'll finally figure out
what life, all of life, is like on Earth.

Thank you.

(Applause)