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Lutz Becks is a professor of limnology at the University of Konstanz’s Department of Biology and director of the university’s Limnological Institute. He will receive approximately 1.8 million euros from the Gordon and Betty Moore Foundation to explore the genetic and cellular mechanisms of symbiosis. His five-year research project entitled “Will you kindly cooperate?” will be funded in the context of the investigator programme of the “Symbiosis in Aquatic Systems Initiative”, which was launched by the Gordon and Betty Moore Foundation in 2019. With a total budget of 140 million US dollars (approximately 130 million euros), the initiative’s aim is to learn how symbioses between microorganisms function and evolve in marine and freshwater environments.

Why do two individuals enter into a symbiotic relationship?

The term symbiosis in its broadest sense is used to describe life forms of two different species that live together and whose survival and reproduction depends on their interaction. “Symbioses have significantly shaped the evolution of life and diversity on earth”, says Becks. “This includes plants as well as the mitochondria in human cells. We are thus talking about very basic mechanisms of life”. He will not only study why two individuals enter into symbiotic relationships, but also explore which environmental conditions favour or hinder the evolution of symbiotic life forms.

“There are at least two ideas as to how symbioses may evolve: One idea is that both partners benefit from each other right from the beginning. The other idea is that one partner exploits the other and retains that relationship over the long term”, Becks explains. So far, research has provided evidence for both hypotheses, whose probabilities Professor Becks will investigate in the context of his new project using experimental evolution. “We will have to study a very large number of replicates in order to verify probabilities”, he says. “To do so, we need automated methods that allow us to work on many replicates simultaneously and over long periods of time and to compare them.” Such methods include, for example, pipetting robots or automated imaging processes that allow the researchers to detect changes at the cellular level that are caused by the evolution of symbiosis.

Under which environmental conditions can stable symbiosis evolve?

For his study Becks uses the green alga Chlorella as symbiont and the paramecium Paramecium bursaria as host. Together, both organisms comprise a perfect model system because their interactions are comparable to one of the processes that led to the evolution of green plants. In the experiments, the algae and paramecia are exposed to different environmental conditions. This way Becks’s team can understand under which conditions symbioses evolve. An important question for the researcher is whether the symbiont is transferred from the mother cell to the daughter cell, or whether the daughter cell itself takes up new symbionts from the environment.

“We create different environments, expose our organisms to these conditions and let them grow over many generations,” Becks explains. This method is called experimental evolution. One experimental condition that will be tested is the addition of Chloroviruses to the algae and paramecia. The viruses infect the algae and can thus influence the conditions for the evolution of a symbiosis. The researchers then compare whether one condition – rather than the other – has led to the evolution of certain traits such as symbiosis.

In theory, a stable symbiosis is much more likely to evolve if the symbiont is transferred only from the mother to the daughter cell. In long-term studies this theory can be tested by manipulating the environmental conditions. Accordingly, parts of the population are exposed to new environmental conditions throughout the entire study. The changes that occur over time are closely monitored by sampling and examining single individuals. “We especially want to find out how dependent host and symbiont are on each other at different time points during the experiment. One way of testing this is to separate them again and see whether they continue to grow and reproduce”, says Becks. At the same time, the scientists use genomic analyses to investigate whether and which genetic changes occur. “When you arrive at the point in an experiment when a Paramecium that is not actually green turns green – which means that it has taken in a symbiont – then this is a wonderful experience”.

Facts:

• University of Konstanz limnologist Professor Lutz Becks awarded funding in the amount of approximately EUR 1.8 million by the Gordon and Betty Moore Foundation.
• The five-year research project will explore the genetic and cellular mechanisms of symbiosis as well as the environmental conditions that favour or hinder the evolution of symbiotic life forms.
• Funding amount: Approx. EUR 1.8 million.
• Funding period: Five years.