Complex photonic response reveals three-dimensional self-organization of structural coloured bacterial colonies.

Gianni Jacucci,Lukas Schertel,Laura Catón,Colin J. Ingham,Silvia Vignolini,Gea T. van de Kerkhof,Bodo D. Wilts,Villads E. Johansen,Yu Ogawa

doi:10.1098/rsif.2020.0196

Abstract

Vivid colours found in living organisms are often the result of scattering from hierarchical nanostructures, where the interplay between order and disorder in their packing defines visual appearance. In the case of Flavobacterium IR1, the complex arrangement of the cells in polycrystalline three-dimensional lattices is found to be a distinctive fingerprint of colony organization. By combining analytical analysis of the angle-resolved scattering response of in vivo bacterial colonies with numerical modelling, we show that we can assess the inter-cell 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 response enables a precise understanding of the structural organization of the bacteria.

Highlights

Iridescent structural colours originate from the interference of light scattered from transparent materials organized at a nanoscale level
An overview of the structural organization of IR1 bacterial colonies is obtained with a combination of electron microscopy (EM) techniques (scanning EM (SEM), cryogenic-SEM and transmission EM(TEM)) as shown in figure 1c–f
The positions of the bacteria are strongly correlated in space and this correlation can be observed across all the colony

Summary

Introduction

Iridescent structural colours originate from the interference of light scattered from transparent materials organized at a nanoscale level. In contrast to dye/ pigmentation-based coloration originating from absorption, such structural colours allow living organisms to fully control their visual appearance both in terms of colour and angular distribution. A detailed explanation on how the interplay between order and disorder in their packing dominates the optical appearance in this system remain unclear. Such knowledge would allow insights into bacterial colony behaviour and enables their use as living optical materials

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