The Level of Noise Controls the Efficiency of Natural Selection in Growing Biofilms
von Fabian Stiewe
Datum der mündl. Prüfung:2014-12-11
Betreuer:Dr. Oskar Hallatschek
Gutachter:Prof. Dr. Christoph F. Schmidt
Gutachter:Dr. Eleni Katifori
EnglischMany microbes live in biofilms, which are spatially structured populations. During adaptation to a new environment, beneficial mutations occur, and some of them spread through the population. Others go extinct due to noise in the life cycle and reproduction process. This noise is called genetic drift. Growing biofilms are an example of populations undergoing a range expansion. The level of noise in growing biofilms differs strongly between species. However, the effect of these different noise levels on the establishment of beneficial mutations has not yet been quantified. Here we show, that the observed differences in noise level indeed lead to large differences in the establishment rates of beneficial mutations. We found establishment rates of S. cerevisiae and spherical E.coli strains to be 1–2 orders of magnitude larger than establishment rates of rod-like strains of E. coli. Furthermore we observed that the noise level can be tuned via growth temperature, and that the establishment rates measured at different temperatures are consistent with the respective noise levels. Our results suggest that the efficiency of natural selection in biofilms strongly depends on the species and growth conditions. The method presented in this study can be used to test the dependence of establishment rates on other parameters and for many microbial species easily.
Keywords: Adaptation; Biofilms; Genetic Drift; Spatial Structure; Range Expansions; Natural Selection; Establishment of Mutations; Microbial Evolution