In the springtime, after the first warm rain, that’s when the spotted salamanders start
getting on the move.
And then they lay all these beautiful little egg masses out in all the ponds
across the East Coast.
So, we go out there in our waders, collect egg masses, and then set up different ways
of studying them in the lab.
My name is John Burns and I’m a post-doctoral researcher in the
Division of Invertebrate Zoology.
Deep inside this bowl there are cells that are interacting between the world of algae
and the world of salamanders. And so we want to get in on that action and figure out
what’s going on.
I’m Ryan Kerney. I’m an assistant professor of biology at Gettysburg College and a research
associate here at the American Museum of Natural History.
We’re really interested in a symbiosis that exists between the salamander embryos and
an algae.
Symbiosis refers to the living together of two or more different organisms.
I’m Eunsoo Kim. I’m an assistant curator of microbial diversity and systematics in
the Division of Invertebrate Zoology.
So, you can find algae in most of the aquatic environments like pond water in Central Park.
You just put a drop of water on the microscope slide and take a look at them and you will
find at least some of them swimming.
Here at the Museum, we maintain about 80 live cultures of microorganisms, including algae.
And about half of them are unique to our collection.
In the case of salamander and green algae, during the embryonic stage, algal cells live
basically inside of the egg.
The association between the spotted salamander and this green algae was first described in
1888 by a naturalist-scientist named Henry Orr. He basically just started wondering what
is going on that the salamanders allow all these green algae
to live inside their egg case.
It would be like having a bunch of green algae inside of the womb, which is totally bizarre.
And then over time, people started to study it. So, they found that when the sun is out,
the algae are producing oxygen inside the egg mass. So, if you try to kill the algae
or you keep them in the dark, the salamanders will be smaller, and they might have a poorer
chance of survival post-hatching without the benefit of the extra oxygen.
The algae may benefit because of nitrogen that’s a waste product for the salamander,
but that can be utilized for their cells’ metabolism.
We’re pretty sure that the algae are able to grow to high densities and they get some
nutrients that they would not be able to get outside in the pond.
Our initial question was how is it that a beneficial microbe—this algae—is able
to get through the big jelly that surrounds the embryos and the individual egg capsules
that the embryos live in. We wanted to look at this association a little bit more closely
through the microscope.
The algae, like all photosynthetic life, has these pigments that fluoresce. That means
that if we shine light on them of one wavelength, they emit light of a different wavelength.
And basically on a lark, I looked at a later stage embryo with a fluorescent microscope
to see if there was any sign of algae, you know, persisting near the time of hatching.
And it was really surprising to see that there’s algal cells embedded inside the embryo itself,
inside the tissues.
Then we wanted to look at the inside of cells. And we were able to see that the algae is actually
going inside the cells, the individual cells of the embryo. Which was a real high-five
moment around the microscope to see this cool interaction that was really unexpected.
That cell within a cell relationship—like a Russian matryoshka doll—occurs in giant
clams. It occurs in corals. It occurs in sea slugs. But there are no other real known examples
of a symbiont entering into the cells of a vertebrate.
The question that we are currently tackling is what kind of molecular change is happening
when these salamander cells and green algal cells are together.
We took cells from four different groups—salamander cells that have algae, salamander cells that
didn’t have algae, the algae cells that were living inside the salamander cells, and
the algae living in the egg capsules.
And what we did was we basically just counted how many of each type of RNA there were and
then we compared them to one another.
We actually are starting to know how these two species are adapting to each other. Like,
you know, for example, the algae actually, when they get inside the salamander cells,
it’s a super nutrient-rich environment. So, they turn off the genes associated with
importing inorganic nutrients. Because they don’t need them anymore. They’re flooded
with them.
We are learning that these two fundamentally different cells, they're really changing each
other very dramatically. And this change may be relevant for other symbiotic systems, including
like human and parasitic bacteria relationships.
Researchers are increasingly interested in how the microorganisms that are inside and
on our bodies interact with us throughout the course of our lives and affect our physiology.
So, this project really is in keeping with the sort of research attention of today. Will
it potentially show us some new way about how life on Earth interacts with one another?
That’s what we really hope for. And to just be part of that conversation is extremely
exciting right now.