AcademiaNet: Dr Guse, your laboratory focuses on symbiosis – the mutually beneficial association of two different species – of algae with corals and sea anemones. How would you describe your research?
Dr Guse: In principle we are interested in coral symbiosis. Corals are animals, and they live together in reefs in nutrient-poor areas of the ocean. To survive in these regions, they form a symbiosis. They live together with algae which can produce nutrients from sunlight. The algae live inside the coral cells, performs photosynthesis and gives off energy to its host. This is how these two organisms survive together.
Our lab is working with a sea anemone as model system for corals. There are several reasons why we do that. Corals are protected animals – you cannot simply pick them up from the ocean floor take them with you. Additionally, it is difficult to keep them in an aquarium, and it takes a long time until they are sexually mature. This is why we take the sea anemone as a kind of proxy. We decided to use Aiptasisa because it has the same algae symbionts as the corals.
Our sea anemones are growing very quickly – aquarium owners commonly consider them a pest. They reproduce asexually: from one animal, you can make a thousand genetically identical ones. We are working with "clonal lines" of Aiptasia, which are derived from 3 animals. The same lines are used in other labs around the world. This is how we can really analyse the importance of single genes on processes within these animals.
How could one imagine this asexual reproduction?
Every sea anemone has a kind of foot, a stem and tentacles. When they reproduce asexually, small cell masses start to form at their feet. Within a week, they develop into little, independent sea anemones – in a way like baby cactuses, that form on top of the mother plant.
What exactly does your research focus on?
We are particularly interested in how symbioses are established. Most corals produce offspring that is free of symbionts. They reproduce sexually – there are male and female corals, and together they produce larvae. The larvae have to take up their symbionts from the environment. For corals, this event only happens once a year, correlating with a full moon in spring. So only once a year you get a chance to study symbiont acquisition on the animals.
We can recapitulate the whole process in the lab with the sea anemone we are working with. We induce the sexual maturation and production of gametes with bluelight-LEDs. This way, we can produce offspring each week and use the larvae for our experiments. The larvae swim around and take up the symbionts. Both are very small, so we can put them under a microscope and watch the whole process.
With these larvae, we study fundamental features of symbiosis establishment. We are investigating several aspects of this process: How are the symbionts recognised? Which molecular mechanisms and key molecules are responsible for their take-up? Then we are also interested in the nutrient exchange and the cell-cell interaction of these very dissimilar cells. In principle, they are an animal and a plant cell, forming one entity.
So the algae are living within the coral or the anemone, but they are still foreign organisms. Why is the coral not recognising the intruders as a potential danger and have its immune system attack them?
That is a very interesting, and still open, question. Normally an animal cell would digest any intruders with the help of its immune system. But the symbiont is avoiding this somehow. There are several theories on how it may achieve that. Most people believe the mechanism must be similar to that of parasites. Many intracellular pathogens, including the Malaria parasite Plasmodium , have developed mechanisms to actively manipulate the host cell and prevent it from digesting them. It is possible that the symbiont does this in a very similar way. But it is also possible that it is recognised as something positive because it delivers nutrients to the host. What actually happens is something we would love to find out.
Part of your research is also done on corals themselves. Where do your test subjects come from?
Our anemones are kept under controlled conditions in incubators. In addition, we are doing some comparative research on corals. Once a year, we travel to Okinawa in Japan with a Japanese collaborator. We go there exactly then the corals are about to reproduce. In Japan, we go snorkling and we collect corals in the sea. Then, shortly before their expected spawning date, we put them in special tanks and wait for them to shed their gametes. Once they are ready for experiments, we collect the larvae. It takes several days for them to develop and reach this stage.
Our Japanese colleagues take the animals with them to Tokyo, but for us this is more difficult: corals need fresh sea water, which we can't easily procure in Heidelberg. In addition, the flight is very long and straining for the animals. Last time we tried to take samples home, we ran into problems: it probably got too cold in the plane, and the corals didn't like that. This is why we do important experiments while we are in Japan – which means we are on site for a relatively long period of time.
Is the fieldwork a big challenge?
It is very laborious. Everyone thinks, "Oh, a holiday in the tropics!" … But actually it is exhausting. You end up working up to 16 hours a day, and your time and resources are always limited. Also, fieldwork is not everyone's kind of thing – which initially surprised me, because I love to do it.
But once you come back to the lab, you know why you usually work there. Most of the time, in the field, something goes wrong. You always have to be prepared that the experiments that you have planned for so long don't work as you anticipated: You may not have enough time, an important sample is lost or the corals don't spawn when they should. You've got be flexible, and have a plan B.
Which questions would you like to study next?
We want to elucidate the molecular mechanisms of the acquisition of the symbionts. Moreover, we would like to improve our experimental model further, particularly in respect to live imaging. Currently, we are working hard on making the sea anemone genetically manipulable – and we have made some big advanced on that recently. We can already microinject, which means we can bring RNA or DNA into the embryo and then study specific genes.
We however have one problem left with our system: we cannot study the whole life cycle of our sea anemones. We can produce larvae every week, but we haven't managed for them to go into metamorphosis yet. The larvae swim around, but they don't settle to become the mature sea anemones. For this to happen, they rely on specific cues – we just don't know, what these signals are. Several labs have been working on finding them, but so far without success. This is one of the big topics in our area of research, and it is also one of the things, we would like to look into in the future.
What do you do to relax after a stressful day at work?
I go jogging more or less regularly. I enjoy cooking and meeting my friends. Asides, I am tending my aquarium and – whenever I get the chance – I snorkel or dive. My job actually almost feels like a hobby to me!
Michaela Maya-Mrschtik conducted the interview for AcademiaNet.