Differential Interaction Forces Govern Bacterial Sorting and Stability in Early Biofilms

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Physical interactions and in particular mechanical forces are involved in sorting of different cell types. These requirements have been established in the field of embryonic development [3]. The development of bacterial biofilms resembles eukaryotic development in various aspects [4]. In comparison, the bacterial cell body in our model can be considered as a point-object and the forces of pilus retraction are always attractive.We have tested the hypothesis that differential physical interactions between bacteria cause cell sorting in early biofilms [2]. We generated a toolbox of gonococcal type IV pili varying in number per bacterium and pilus-pilus rupture forces. The morphotypes of mixed microcolonies were in remarkable agreement with the predictions of the differential strength of adhesion hypothesis proposing that cells sort based on differential net rupture forces. Our findings suggest that similar to embryonic development, mechanical forces govern cell sorting in early biofilm formation. Furthermore we demonstrated that oxygen is required for gonococcal microcolony formation by enhancing pilus-pilus interaction [1]. Mechanistically, the strength of pilus-pilus interaction decreases with oxygen depletion and influences the microcolony stability.We conclude that differential cell-cell interactions govern the formation of and sorting within early bacterial biofilms.1.Lena Dewenter∗, Thorsten E. Volkmann and Berenike Maier; (2015) Oxygen governs gonococcal microcolony stability by enhancing the interaction force between type IV pili. Integr. Biol., 10.1039/c5ib00018a2.Enno R Oldewurtel, Nadzeya Kouzel, Lena Dewenter∗, Katja Henseler, Berenike Maier; (2015) Differential interaction forces govern bacterial sorting in early biofilms. eLife, 10.7554/eLife.108113.Gonzalez-Rodriguez D, Guevorkian K, Douezan S,Brochard-Wyart F (2012) Soft matter models of developing tissues and tumors. Science 338: 910-917. 5694.Monds RD, O'Toole GA (2009) The developmental model of microbial biofilms: ten years of a paradigm up for review. Trends in microbiology 17: 73-87.