The multi-dimensionality of social interactions in Pseudomonas communities
Evolution, Anthropology
Final Report Abstract
Bacteria are social organisms. They frequently cooperate by secreting costly metabolites such as enzymes and metal-chelating agents. These extracellular products are often referred to as ‘public goods’, because the can benefit individuals other than the producer. Numerous studies now show the social interactions resulting from the secretion of a single type of public good can play a crucial role during host infection and in various biotechnological and environmental processes. However, it is currently unclear how the simultaneous production and availability of multiple public goods affect the functioning of bacterial communities, and drive the evolution of social traits in nature. In my postdoc project, we aimed to unravel this conundrum by studying multiple public good traits and the social interactions resulting from their simultaneous production in natural soil and freshwater communities of Pseudomonas bacteria. In a first step, we screened over 300 natural isolates for their production of five important public goods, including siderophores used to scavenge iron and proteases used to digest extracellular proteins. We showed that natural isolates varied dramatically in the extent to which they invest in social traits, and that correlations between social traits occurred frequently, were exclusively positive, and in some cases habitat-specific. Our results suggest that public-good-based interactions might often be shaped by trait linkage and the resulting pleiotropic effects. Moreover, they indicate that most strains either express multiple social traits at high levels or show little investment into any social trait, which suggests a limited scope for a reciprocal exchange of different public goods among strains with specialized trait repertoires. In a second step, we focused on siderophores and proteases to investigate how frequently strains can capitalize upon the public goods produced by community members. Contrary to our expectations, we found that the natural isolates did not reliably secrete proteases under conditions that had previously been described to induce their production. Moreover, we showed that proteases often did not benefit their producer even if they were produced at high levels. These results suggest that proteases might not always act as a public good. By contrast, we found that siderophores generally benefitted their producer, and at least sometimes favored the growth of other strains. Indeed, our results seem to suggest that the potential for positive interactions among natural Pseudomonas isolates is higher under conditions inducing siderophore production and sharing. We are currently investigating this notion by testing how siderophore-based interactions affect the productivity and stability of our Pseudomonas communities. Overall, our results highlight that the ‘goodness’ of secreted compounds is highly context-dependent. Moreover, they point to a crucial role of siderophores in structuring bacterial communities, a notion that we have corroborated in a number of side-projects including a large-scale literature review.
Publications
- (2020). Bacterial siderophores in community and host interactions. Nature Reviews Microbiology 18, 152-163
Kramer J, Özkaya Ö, and Kümmerli R
(See online at https://doi.org/10.1038/s41579-019-0284-4) - (2020). Competition for iron drives phytopathogen control by natural rhizosphere microbiomes. Nature Microbiology
Gu S, Wei Z, Shao Z, Friman V-P, Cao K, Yang T, Kramer J, Wang X, Li M, Mei X, Xu Y, Shen Q, Kümmerli R, and Jousset A
(See online at https://doi.org/10.1038/s41564-020-0719-8) - (2020). Cooperation and conflict within the microbiota and their effects on animal hosts. Frontiers in Ecology and Evolution 8:132
Figueiredo ART and Kramer J
(See online at https://doi.org/10.3389/fevo.2020.00132) - (2020). Positive linkage between bacterial social traits reveals that homogeneous rather than specialised behavioral repertoires prevail in natural Pseudomonas communities. FEMS Microbiology Ecology 96, fiz185
Kramer J, Lopéz Carrasco MÁ, and Kümmerli R
(See online at https://doi.org/10.1093/femsec/fiz185)
