Phase behavior of bacterial binary mixtures
Final Report Abstract
The spatiotemporal organization of microbial communities plays a critical role in their functioning and success in the environment, with impacts from health to agriculture and industry. While biochemical interactions are extensively studied, how physical interactions contribute to structuring typically multispecies and phenotypically diverse bacterial communities was unclear. In particular, many bacterial populations feature a mix of motile and non-motile cells of either coexisting species or phenotypically differentiated clones. In this research project, we sought to unravel the physical effects of the drive out of equilibrium due to active motility on the organization of bacterial communities. To this aim, we established a controlled model system of mixed motile and non-motile Escherichia coli bacteria. We first studied how this heterogeneous population organizes in liquid suspension at rest. We found that the motile cells induce large-scale, fluctuating density patterns of non-motile bacteria across a wide range of physiologically relevant cell densities. Our published experimental and modeling work showed that this pattern formation solely results from physical interactions and relies on two key ingredients: swimmer-induced flows advecting non-motile cells, and, more unexpectedly, vertical symmetry breaking by sedimentation permitting their local accumulation. The properties of this new pattern-formation mechanism highlight the importance of longrange hydrodynamics over short-range polar effects in active bacterial systems. We next investigated how these patterns affect non-motile cell aggregation and the eventual formation of mixed biofilms. We found that motile bacteria strongly accelerate the formation of larger, more compact non-motile aggregates, with the notable benefit of higher survival to bactericidal treatment. At long time, as the mixture grows into a surface-attached biofilm, the initial aggregation favors the formation of a spatially structured biofilm, whereas two isophenotypic strains remain well mixed. We finally investigated how the mixed community organizes under flow, a ubiquitous constraint for bacteria. The binary mixture subjected to microfluidic flows showed a swimming-dependent segregation of non-motile cells: They were advected and accumulated to one side of the channel, where an asymmetric biofilm could eventually form. Experiments and modeling elucidated the mechanism: Swimming cells experience sideward rheotaxis due to flow shear and induce a backflow that advects the non-motile cells. Sedimentation is again crucial to induce non-motile cell accumulation, whereas motile cells recirculate along the channel walls. This new active phenomenon demonstrate the importance of physical constraint in mixed microbial communities.
Publications
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Multiple functions of flagellar motility and chemotaxis in bacterial physiology. FEMS Microbiology Reviews, 45(6).
Colin, Remy; Ni, Bin; Laganenka, Leanid & Sourjik, Victor
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d-amino acids signal a stress-dependent run-away response in Vibrio cholerae. Nature Microbiology, 8(8), 1549-1560.
Irazoki, Oihane; ter Beek, Josy; Alvarez, Laura; Mateus, André; Colin, Remy; Typas, Athanasios; Savitski, Mikhail M.; Sourjik, Victor; Berntsson, Ronnie P.-A. & Cava, Felipe
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Active Density Pattern Formation in Bacterial Binary Mixtures. PRX Life, 2(2).
Espada Burriel, Silvia & Colin, Remy
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Active segregation in binary mixtures under flow. openRxiv.
Di Dio, Giacomo & Colin, Remy
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Role of a single MCP in evolutionary adaptation of Shewanella putrefaciens for swimming in planktonic and structured environments. openRxiv.
Edelmann, Daniel B.; Jakob, Anna M.; Wilson, Laurence G.; Colin, Remy; Brandt, David; Eck, Frederik; Kalinowski, Joern & Thormann, Kai M.
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Swarming bacteria exhibit developmental phase transitions to establish scattered colonies in new regions. The ISME Journal, 19(1).
Zdimal, Amanda M.; Di Dio, Giacomo; Liu, Wanxiang; Aftab, Tanya; Collins, Taryn; Colin, Remy & Shrivastava, Abhishek
