Ecology of Bacterial Communities: Interactions and Pattern Formation
Final Report Abstract
Ecological systems are highly divers. Mechanisms maintaining biodiversity affect the dynamics of evolving biological systems. Combined theoretical and experimental efforts are needed to reveal the importance of motility as well as interaction, resulting in the coexistence of competing species. In a combined experimental and theoretical study we analyzed the spatio-temporal dynamics of interacting bacterial populations for two paradigmatic scenarios: (i) range expansion and (ii) extended spatial systems. For the range expansion scenario we studied the effect of several parameters such as growth rate and lag-time, in addition to the presence of the toxin Colicin on the composition of mixed bacterial populations in expanding colonies. The studied Escherichia coli Colicin E2 system comprises three strains; the toxin producing strain (C), a strain sensitive to the toxin (S) and a resistant strain (R). We observed either dominance of the R strain or coexistence of two strains (R/C or R/S). Combining experimental analysis with theoretical modeling we found that robust three-strain coexistence requires a balance between growth rates and either a reduced initial ratio of the toxin-producing strain, or a sufficiently short toxicity range. In addition, we studied the role of mutations and phenotypic heterogeneity on the composition of a population at an expanding front. We found that mutations towards slower growth rates can promote coexistence of wild-type and mutant strains. In a population composed of cells that may either be able to divide or be flagellated and thereby able to move, we observed that the population is asymptotically dominated by individuals following a 'bet-hedging' strategy with approximately equal rates for motility and reproduction. Taken together, these findings highlight the complex interplay between internal dynamics and front expansion for the composition of expanding microbial populations. For spatially extended systems we performed theoretical studies focusing on the effect of mobility and turbulent flow on the biodiversity of populations with cyclic interactions. We first introduced global attractors as a useful concept to characterize the stationary state of the population. Employing this concept, we then showed how the interplay between diffusion and turbulent flow affects biodiversity. Finally, we explored how increasing the complexity of the interaction network by adding an additional toxin producing species affects the composition of the population. Our main finding in the latter study is that the strength of diffusive mixing determines which sub-network of species will survive in the long run.
Publications
- Range expansion with mutation and selection: dynamical phase transition in a two-species Eden model. New J. Phys. 13:113013 (2011)
J.-T. Kuhr, M. Leisner, E. Frey
- Global attractors and extinction dynamics of cyclically competing species. Phys. Rev. E 87:052710 (2013)
S. Rulands, A. Zielinski, E. Frey
(See online at https://doi.org/10.1103/PhysRevE.87.052710) - High variation of fluorescence protein maturation times in closely related E. coli strains. PLoS ONE, 8(10):e75991 (2013)
E. Hebisch, J. Knebel, J. Landsberg, E. Frey, M. Leisner
- Chemical warfare and survival strategies in bacterial range expansions. J. R. Soc. Interface, 11:962014172 (2014)
M.F. Weber, G. Poxleitner, E. Hebisch, E. Frey, M. Opitz
(See online at https://doi.org/10.1098/rsif.2014.0172) - Mobility-dependent selection of competing strategy associations. Phys. Rev. E 89:012721 (2014)
A. Dobrinevsky, M. Alava, T. Reichenbach, E. Frey
(See online at https://doi.org/10.1103/PhysRevE.89.012721) - Range expansion of heterogeneous populations. Phys. Rev. Lett. 112:148103 (2014)
M. Reiter, S. Rulands, E. Frey
(See online at https://doi.org/10.1103/PhysRevLett.112.148103) - How turbulence regulates biodiversity in systems with cyclic competition. Phys. Rev. E 91:033009 (2015)
D. Groselj, F. Jenko, E. Frey
(See online at https://doi.org/10.1103/PhysRevE.91.033009)
