  Bacterial biofilms are usually assumed to originate from individual cells
deposited on a surface. However, many biofilm-forming bacteria tend to
aggregate in the planktonic phase so that it is possible that many natural and
infectious biofilms originate wholly or partially from pre-formed cell
aggregates. Here, we use agent-based computer simulations to investigate the
role of pre-formed aggregates in biofilm development. Focusing on the initial
shape the aggregate forms on the surface, we find that the degree of spreading
of an aggregate on a surface can play an important role in determining its
eventual fate during biofilm development. Specifically, initially spread
aggregates perform better when competition with surrounding unaggregated
bacterial cells is low, while initially rounded aggregates perform better when
competition with surrounding unaggregated cells is high. These contrasting
outcomes are governed by a trade-off between aggregate surface area and height.
Our results provide new insight into biofilm formation and development, and
reveal new factors that may be at play in the social evolution of biofilm
communities.
