Interplay between order and disorder in natural photonic structures

Colours in natural systems, e.g. bird feathers, butterfly wings or the peacock, are often created by scattering of nanostructured materials, rather than the common absorption mechanism of dyes. Bacterial colonies of Flavobacterium strain IR1 were discovered to possess incredibly bright structural colouration [1] . The 2D hexagonal crystalline arrangement of the cells is found to be a distinctive fingerprint of the colony organisation [2] . By combining analytical analysis of the angle-resolved scattering response of in-vivo bacterial colonies with numerical modelling, we show that we can access to the inter-cells distance and cell diameter with a resolution below 10 nm, far better than what can be achieved with conventional electron microscopy, suffering from preparation artefacts. Retrieving the role of disorder at different length scales from the salient features in the scattering spectra enables to obtain a precise understanding of the structural organisation of the bacteria in three dimensions and to gather insights into their metabolism relevant for inter-cellular communication. These measurements of intercellular distances within Flavobacterium colonies enable to study the physical interactions of cells during adaptation of the colony structure to environmental conditions, such as nutrient content and allows the use of their structural colour for biosensing applications.