Self-affine growth of bacterial colonies

In this paper the scaling behaviour of the surface of Escherichia coli and Bacillus subtilis colonies growing on agar plates are studied. We present the first experimental evidence for the self-affine fractal nature of the shape of a biological system. The value H ≃0.78 we obtained for the roughness exponent H describing the scaling of the surface width indicates that the development of the surface is subject to correlations due to the complexity of bacterial colony formation.