MPI-CE Institutsseminar

<b<Abstract:</b>
In nature, most bacteria strive in surface-attached sedentary communities known as biofilms. Biofilms have become a key example of bacterial complexity. Many cells inhabiting a biofilm express cooperative traits, like the secretion of extracellular polysaccharides (EPS). These traits are beneficial at the biofilm level, because they enhance the stress resilience of a biofilm or its capacity to grow, while the costs occur at the cell level. In well-mixed populations cooperation is difficult to achieve, because cheaters can reap the benefits of cooperation without having to pay the costs. The physical process of biofilm growth can however result in spatial segregation that prevents cheaters from exploiting these benefits. Here, the effect of colonization conditions on cooperation will be discussed for Bacillus subtilis biofilms. By manipulating the density of founder cells, both in a mathematical model and in laboratory experiments, it is shown that colonization at low densities favors spatial segregation and cooperation, that is, the costly production of EPS that facilitates the spread of the biofilm. Competition experiments reveal that EPS-producing cells have a selective advantage over non-cooperative mutants when colonization occurs at low densities, while they have a disadvantage when initial cell densities are high. This underscores the importance of the ecological setting for understanding the evolution of microbial cooperation.