Spatial patterning and self-assembly in microbial populations

Microbes in nature often do not live as individual cells suspended in liquid (as in typical lab cultures) but rather as dense aggregates of cells which, when attached to surfaces, are known as biofilms. Biofilms are responsible for many chronic infections, especially when they form on medical implants, and are also the cause of much industrial damage, through "biofouling". However they are also beautiful examples of non-equilibrium self-assembly, and can be thought of as a model system for multicellular self-assembly processes more generally. In a project funded by the Human Frontiers Science Program, I, Vernita Gordon (UT Austin), Thomas Bjarnsholt (U. Copenhagen) and Steve Diggle (U. Nottingham), are investigating how the spatial structure of a biofilm develops. In particular we have found that the presence of small clumps of cells at the start of biofilm growth can have a drastic effect on the final structure. This project involves confocal microsopy (Gordon and Bjarnsholt groups), biofilm evolution experiments (Diggle group) and individual-based computer simulations (carried out by Gavin Melaugh in my group).
 
A "simpler" example of multicellular self-assembly involves the formation of bacterial colonies on soft gel surfaces. Colony formation is standard in the microbiological lab but it is not often studied as a self-assembly process. Together with Diarmuid Lloyd, I have been studying how bacterial cells compete for space as they spread to colonies an agarose gel surface. I have also collaborated with Pietro Cicuta in Cambridge and with Bartek Waclaw here in Edinburgh to investigate how colonies that are initially growing in two dimensions (a flat layer on the agarose gel surface) "buckle" to form a second layer that invades the agarose. More recently, I have been working with Diarmuid Lloyd, and with Wilson Poon, Bartek Waclaw and their students, to understand this 2D-3D transition in more detail.

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