Holly Moeller Finds Keys to Ecology in Cells That Steal

There are organisms that eat their neighbors to get ahead in nature. Holly Moeller is an assistant professor of ecology, evolution and marine biology at the University of California, Santa Barbara.

Protists are unicellular organisms that don't fit into the categories of animals, plants and fungi. Some protists are able to co-opt parts of the cells they prey on. Protists can expand into new habitats and survive where they couldn't before with the help of these still functioning pieces of their prey.

Moeller has a unique view of the underlying structure of the ecosystems today, thanks to watching them. The protists' pilfering of the cells' mitochondria is related to the acquisition of metabolism by our ancestors.

These are questions about when and how organisms specialize and how they can break that specialization by gaining access to something new. This work addresses questions about how organisms expand their ecological niche, how those acquisitions can be permanent, and how metabolism jumps across the tips of the trees of life.

She spoke with Moeller about her career and research. The interview has been edited to make it clearer.

You’ve become well known in ecology and evolution circles for your work on “acquired metabolism.” Is that a term you came up with?

It wasn't intentional. There are parts of your metabolism that are not in your own genome. You can get access to them by being associated with another species.

Sitting in a dark room, looking through a microscope, feels like you sense the personality of these different species.

It is more than that and includes some forms of symbiosis. It also includes things like horizontal gene transfer, where a single gene or a whole package of genes is plucked from one person to another.

I am interested in the roles that organisms play in the environment and how niches grow and contract over time. The study of acquired metabolism is related to how organisms can expand their niches.

Is what humans have with our gut bacteria acquired metabolism?

That is a good example. Our ability to eat diverse food sources and metabolize them is dependent on the amount ofbacteria we have. The vitamins and cofactors that we need, likevitamin K, are manufactured by the bugs in our gut. These partnerships are very important to us.

What led you into this line of research?

It's a process calledumbling and running. When the signal stops, they spin and go off in a different direction. This is true for many scientists as well. We follow our noses and chase after things that we are excited about. Sometimes it leads to unexpected destinations.

I was able to survive. My parents both trained as scientists, and although neither of them worked as one while I was growing up, I knew that research was a career choice. In my undergraduate education at Rutgers University, I was connected with a faculty member doing research on marine microbes, thanks to the professors who took an interest in me. Paul Falkowski is a scientist I worked with. One of the things he was studying was how the tree of life was spread.

My interest in metabolism started here. The idea that a feature of plants was actually something they got a couple billion years ago by eating a bacterium was fascinating. This has occurred many times. I began working with Paul and Matt Johnson, who were his coworkers at the time, on organisms that might tell us about the evolutionary process.

I love the idea that an organism can start out in life without a chloroplast, and then just pick one up.

Yes, right? Imagine if we had a salad and our arms were green. I live in Southern California and can take a walk between classes if I need to. I don't think I would enjoy eating lunch.

They need to eat the nucleus.

In a lot of cases, the organisms that obtains are bound to doing photosynthesis. Some of the species that we work on are unable to survive if they can't find prey. I am curious to know if they backed themselves into this corner.

Do these species have to keep stealing chloroplasts because they eventually break down?

Yes, it's generally. The genes that steal the chloroplast vary in how well they maintain it. Some of the marine ciliates that we work on don't steal from the chloroplasts. Some people run them into the ground quickly. Stealing functional nuclei from their prey means that they can make more pliches.

The child who has never stolen a car is like the one that doesn't steal chloroplasts. Some people steal a car and crash it into a tree. There are people who steal a car and build a mechanic shop to take care of the stolen property.

We can ask about the evolutionary differences between the organisms that facilitate the transitions.

Do they ever inherit chloroplasts from their parent cells? If the cells divide to reproduce, don’t the chloroplasts get passed on as well?

Some of them are able to. The cells split up the allotted space when they divide. They need to eat to refresh and replenish their cells.

The cells that keep the stolen nucleus can cause the cells in the rest of the cell to split. They need to eat the nucleus. They hang on to the cells when they catch them. It seems like the most important thing is that they pick up new particles.

That is a fascinating question. Most of the prey cell is eaten by some of the Mesodinium ciliates. Even though the chloroplasts are intact, they are still in the relic cell of the prey. The ciliate stuck the prey cell into a vacuole when it ate it.

We don't know howmolecules are moving We are trying to find out more about that by following where theProteins are going.

What evolutionary question is this work helping you answer?

When we teach photosynthesis in school, we mainly focus on the land plants, whose ancestors picked up chloroplasts 2 billion years ago.

There is more to the picture when we look at the ocean and freshwater systems. When we look at organisms that have a secondary chloroplast, we mean that they got it from something else in their evolution. You can sometimes see evidence of tertiary chloroplasts, where organisms are getting their chloroplasts from a third cell. We think that there have been at least half a dozen secondary and tertiary events. That has given rise to a lot of different types of plants.

Is it possible to go from being something that's Heterotrophic to something that's Highly Potent? What changes need to be made to your body? Where are you going to live? Natural selection has to be in place. What that transition looked like was given insight by the study of Mesodinium.

Does acquired metabolism help organisms get ahead?

In the paper that we published earlier this year, we looked at an organisms that is turning into a source of energy. It is both acquired metabolism and aycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizal ycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizalycorrhizal The Paramecium bursaria are freshwater ciliates that can be popped open and isolated from the rest of the world.

The paramecia are small green blobs in the petri dish. The competitive abilities of these organisms were dependent on the availability of light. The more sunlight there is the more energy they should get from it. They were able to compete with other species.

I had a student who tested that idea. There were banks of lights and small flasks of cultures in this incubator. The cultures were put in petri dishes every two days. She counted the number of different ciliates in the droplets.

Within a few weeks, you could see that the white translucent non-photosynthetic ciliates were disappearing and the bright green paramecia was increasing. The competition could be seen before you saw it.

As the light increased, so did the competitive ability of the organisms that hosted the algae. We were able to understand the data behind this phenomenon thanks to the counting of the cells.

So getting these cell counts and building a mathematical model of what was happening was an important part of this?

There's a lot of counting when we run these experiments When I was in graduate school, my colleague said ecology is just the science of counting I was a bit resentful of her statement, but she was correct.

There is a part of me that still thinks that there is no substitute for sitting with your study organisms and falling in love with them. Sitting in a dark room, looking through a microscope, feels like you sense the personality of these different species. There are some paramecia that are translucent and silvery white, because they don't have any photosynthesis. As the experiment goes on, they start swimming fast and you can see them getting hungry before you see them. Observations can lead to more findings.

It's very dangerous to be in high-light settings if you've got a chloroplast. It's possible to get sunburned.

Being able to combine laboratory experiments with mathematical models makes me more transparent about what I think is happening. What are we talking about when we say acquisition of metabolism? How much resources is the cell getting? How does that affect its ability to compete?

We know that acquired metabolism can change competitive ability. That has implications for other acquisition of metabolism as well. Depending on the system, the details that we plug into the model might be different. We have a way to use it.

We talked about competitive advantages that can come from acquired metabolism. But are there downsides to taking over someone else’s metabolism?

It's definitely true. Our metabolism is thought to be the reason we age.

We use oxygen to burn calories and other molecule for energy because of them. The reactive agents produced by the chondritis might be degrading our body's genetic material. It's dangerous to put these things next to your genetics.

The organisms that steal chloroplasts have a lot of protective machinery, which helps them to resist taking on a chloroplast. It's very dangerous to be in high-light settings if you've got a chloroplast. It's possible to get sunburned. According to Suzanne Strom, a scientist at Washington State at Western Washington University, organisms tend to digest cells quicker when there's more light. Light can help you break down the chloroplast. It is possible that the organisms is thinking, "I have to get rid of it"

The types of environments that these organisms might have been living in when they first started hanging on to the chloroplasts is an interesting question. I think it was a lower-light environment because if your digestion depends on light, it will slow it down and reduce the harm that the chloroplasts can do. It can be managed a bit more. It is a low light species. That is very anecdotal More evidence is needed. There are also things that live in a high light environment.

I noticed on your Twitter that you’re doing a lot of tree-root counting. What does that have to do with this other work?

I enjoy being a theoretical ecologist because I can do a lot of different things.

We work on that aspect of metabolism. We've talked about stealing machinery from other organisms. The acquisition of metabolism through this intimate partnership between two organisms is called metabolic mutualism. We are all aware of the business of trees. Trees need water and food from the soil. They gain access to these resources by partnering withycorrhizal fungi. Sometimes they put up delicious mushrooms and other times they are toxic. The trees and the fungi work together. The trees provide sugar from photosynthesis, so they can support each other, and the fungi harvest from the soil, so they can help each other.

This mutualism helps trees to survive in a wide range of environments. A tree can work with different fungi in different environments. We believe this will allow trees to make a living in a more diverse environment than if they were on their own.

There’s so much talk about the microbiome, but we forget that it must have been really difficult to get all those relationships with microbes going at the beginning.

Absolutely. Even if it lives on their outside, most of the time, everything has got at least one type of Microbiome. Who was in charge of Whose evolution? We may have had to deal with the fact that our guts were going to be colonized by bugs and we made the best of it.

The study of acquired metabolism is very interesting. The organisms that are making these acquisitions are being studied. What the selection pressures were and how they were handling that in the past are some of the things you learn about.

I feel like theoretical ecology is exploding lately.

It is very popular now.

Part of the rising interest in theory comes from the amount of information we have. When you have a lot of data, you can come up with some unifying theories about it. There are mathematical models that can be used to solve that problem. There has been more interest in these topics among our graduate students. We have a lot of data. We're prepared.

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