The most important “place” within a bacterium is the mid-point, the place where it divides in order to create two identical daughter cells. It is known that this midpoint is located by proteins, known as Min proteins that oscillate from side to side within the cells.
In work at Delft University, Cees Dekker’s team have managed to tweak E. coli in dramatically geometrical ways to illuminate the mode of action of these proteins. They treated the cells chemically to disable cell division and elongation and then confined them within micro-compartments shaped as circles, triangles, squares and rectangles. Like gourds constrained by ligatures, the cells grew into the shapes defined by their containers. The oscillating proteins were then observed by means of fluorescent markers.
The behaviour of the oscillations showed that the protein system senses the symmetry of the cell: in a triangle it moves between the apex and the centre of the opposite side; in a square it moves side to side but also transversally; the moment a square becomes slightly rectangular, breaking the symmetry, the transverse oscillations disappear. Beside symmetry, the system can sense size – obviously necessary to detect the mid-point of cells of differing sizes.
Not only was Dekker’s team able to demonstrate the geometrical savvy of these proteins, they showed that a Turing reaction-diffusion system can explain the patterns demonstrated by the system. In 1953 Alan Turing predicted that many patterns in nature could be modelled by a simple system of activation and inhibition between two proteins. In Cees’ system, one protein binds to the cell membrane, is unbound by the action of a second protein, thus freeing the protein to travel across the cell to receptors on the opposite side.
Galileo once famously wrote that book of nature “is written in the mathematical language, and the symbols are triangles, circles and other geometrical figures”. He could hardly have imagined such a literal vindication.
Nature Nanotechnology, August 2015, pp. 655-6; 719-26.