The multi-dimensionality of social interactions in Pseudomonas communities

• Applicant: Dr. Jos Kramer
• Subject Area: Microbial Ecology and Applied Microbiology ; Evolution, Anthropology
• Term: from 2018 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405325560

Cooperation is a cornerstone of life, and occurs not only among higher animals, but also among the myriads of allegedly ‘simple’ microbes that dominate the tree of life. Indeed, microbes frequently cooperate by secreting a variety of costly metabolites such as enzymes to digest food, biosurfactants to move on surfaces, and chelating agents to scavenge essential metals. These metabolites typically constitute public goods that can also benefit individuals other than the producer. Public goods cooperation can create substantial benefits at the community level, and might even affect community stability. However, it is also vulnerable to ‘cheating’, since public goods can be exploited by individuals that withhold costly contributions while still reaping the benefit. Numerous studies have revealed that this ‘social dilemma’ can be modulated by mechanisms that maintain cooperation by constraining the fitness of cheating individuals. However, these studies typically focus on a limited number of bacterial strains and consider just one model trait at a time. By contrast, natural bacterial communities usually feature interactions among multiple strains that simultaneously invest into multiple public goods. Hence, it remains poorly understood how the joint effects of such superimposed social dilemmas affect the stability of bacterial communities, and drive the evolution of social traits in nature. The research project outlined here represents a first step towards resolving this conundrum. Focusing on natural communities of Pseudomonas bacteria, I propose four experiments that will establish (1) the public goods repertoire of the constituent bacterial strains, (2) their ability to capitalize on public goods of other strains, (3) the nature of social interactions among strains that produce different public goods, and (4) the stability of bacterial communities under conditions that require access to different public goods. Specifically, I already screend each strain for the production of three key public goods: pyoverdine, a siderophore used to scavange iron; proteases used to digest proteins outside the cell; and biosurfactants used to move on surfaces. I will now test whether non-producers of a particular public good can benefit from the public good produced by other community members. In the next step, I will examine whether two strains producing different public goods compete with each other by exploiting each other’s public good, or whether they engage in a mutually beneficial division of labour that involves the cooperative exchange of public goods. Finally, I will investigate whether between-strain variation in public goods repertoires promotes or hampers the long-term stability of bacterial communities under conditions requiring the expression of different public goods. Together, these experiments will shed light on the complexity of natural bacterial communities, and show how the tug-of-war between cooperation and conflict is resolved in nature.

• DFG Programme: Research Fellowships
• International Connection: Switzerland
• Host: Professor Dr. Rolf Kümmerli