Impact of Biotic Resistance on Microbial Invasions

• Applicant: Dr. Christoph Ratzke
• Subject Area: Microbial Ecology and Applied Microbiology ; Biophysics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540605007

Microbes are true experts in dispersal, because of their small size they can reach even most remote habitats. This culminated in the idea that "everything is everywhere, but, the environment selects" because microbes were assumed as not being limited in their dispersal. Accordingly, microbial invasion was not regarded as an important phenomenon until recently and therefore only barely studied. But, advancements in next-generation sequencing showed that also for microbes dispersal is limited and thus invasion into new territory is an important challenge for them as well. This situation leaves us with a fundamental lack of knowledge about microbial invasion processes, especially their temporal dynamics. Microbes are usually not invading empty space, but are confronted with native species that often make the establishment of the invaders difficult - a property called biotic resistance. Such biotic resistance can, for example, protect us from diseases by hindering the invasion of pathogens. There has been some research on the origin of biotic resistance, but essentially no studies investigated how the invasion dynamics are altered by this phenomenon. However, understanding these temporal invasion dynamics is essential because they decide if an invasion is successful or not. In this work, we want to combine lab experiments with mathematical modeling to explore how biotic resistance impacts microbial invasions, particularly the invasion of pathogens into native communities. For that purpose, we will establish a microbial model system in which we can easily vary the dispersal rate and strength of biotic resistance. Thus, we can systematically study the impact of those properties on invasion success. We will use the obtained data to develop a theoretical framework that predicts invasion dynamics and success based on the interactions between the invader and native microbes. Finally, we will transfer the obtained knowledge to predict the invasion dynamics of a pathogen entering a complex community of gut microbes. From preliminary results we expect the invasion to resemble a continuous wave at weak biotic resistances. An increase in biotic resistance should cause the appearance of "pulsed waves", whereby the invasion speed fluctuates over time. At strong biotic resistance, we expect the complete "pinning" of waves, where the invasion wave stops. Accordingly, we expect that the dispersal rate has to be above a critical value - set by the biotic resistance - to allow invasion at all. This connection should allow us to predict impending invasions. Accordingly, we want to use a simple parameter-free model to predict the success of an invasion even in complex microbial communities, e.g., a pathogen invading a community of gut strains. We are convinced that our findings will not only be relevant in the field of microbiology, but also for ecology and infection research and shed new light onto the understudied phenomenon of microbial invasion.

• DFG Programme: Research Grants