On the mechanical principles of biofilm formation

Bacteria, once thought to be solitary and asocial, can grow in large, dynamic, multi-cellular communities known as biofilms, which consist of bacteria embedded in an extracellular matrix. However, the manner in which these three-dimensional, surface-adhered communities are built in space and time still remains to be shown. Using the human pathogen Vibrio Cholerae as model biofilm former, we examine the growth of biofilms from single founder cells to mature three-dimensional colonies. We find that biofilms grow from disordered, two-dimensional layers into three-dimensional structures with long-range order consisting of vertically aligned cores and horizontally aligned periphery. Using agent-based modelling, we find that verticalization occurs due to mechanical instabilities at the cell-scale and we quantitatively test these predictions by varying the cell lengths, surface roughness and osmotic conditions.