Growth mechanics of a bacterial microcolony

Abstract : In this work, we propose a framework to understand the morphogenesis of two-dimensional microcolonies. In particular, we have explored how growth and adhesion of individual cells compete during microcolony extension. We have shown (i) that isolated cells display an asymmetry in their adhesion, which is higher at the old pole, (ii) that bacterial elongation can result in pushing forces inside the colony. Since the combination of these two effects is expected to produce mechanical stress at the scale of the microcolony, we have developed a method to measure the resulting adhesion forces using deformable substrates. We have demonstrated that focal adhesions are dynamically established and ruptured, with a bias towards the old poles. We have also probed the role of adhesion in the shape of the colony. We have shown that polar adhesion drives the transition from a linear to a two-dimensional growth after the first division. At larger colony sizes, the level of adhesion continues to correlate with the global shape of the colony. Finally, adhesion is involved in the transition from a two-dimensional to a three-dimensional colony. Taken together, our results suggest that the expression of adhesins and their location at the surface of the cells could be levers by which bacteria actively modulate the shape of the group in which they reside.
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Marie-Cécilia Duvernoy. Growth mechanics of a bacterial microcolony. Bacteriology. Université Grenoble Alpes, 2015. English. ⟨NNT : 2015GREAY074⟩. ⟨tel-01388427v2⟩

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