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Fractal Bacteria

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Bacteria are single celled organisms that can do amazing things in multicellular groups, with complex coordinated behaviors emerging from the interaction of genetic networks, chemical environments, and the physics of cell growth. Last year I wrote about the work of Tim Rudge and Fernan Federici and their incredible images of bacterial growth patterns. Their paper, with colleagues from the Haseloff Lab at the University of Cambridge, was recently published in ACS Synthetic Biology, showing how complex fractal patterns in colonies of E. coli emerge simply from the physical interactions of rod shaped cells.

Figure from Rudge et al. "Cell Polarity-Driven Instability Generates Self-Organized, Fractal Patterning of Cell Layers"

In this experiment, E. coli cells are labelled with two colors of fluorescent protein (they are otherwise genetically identical) and seeded at low density onto a surface. As they grow and divide, the rod shaped cells begin to bump into each other, creating jagged boundaries between the two fluorescent populations. These jagged lines are fractal, self-similar at many scales. Using their CellModeller program, the team found that they could accurately model this fractal behavior by including only physical parameters like viscous drag, cell shape, and growth rate, rather than biological properties like cell-cell communication or chemotaxis. Indeed, when they used E. coli mutants that were spherical instead of rod-shaped, the fractal pattern disappeared.

Rudge et al. ACS Synthetic Biology 2013.

Spherical bacteria (right) make a less fractal pattern than rod-shaped ones (left)

It’s fascinating to see how such complex biological patterns can emerge from very simple physical interactions. There is a huge diversity of microbial patterns and multicellular behaviors that arise from differently shaped cells interacting and communicating in different environments with different cell logics. One interesting example cited in the paper is a study of the biophysics of wrinkly biofilms.

Like the fractal E. coli, the Bacillus subtilis cells in the biofilm are subject to physical forces that create patterns as the cells divide and the biofilm expands. The researchers found that the where there were regions of dead cells, those lateral forces would cause the biofilm to buckle vertically, creating 3D wrinkles. They could generate “synthetic wrinkle patterns” by painting denser regions of cells that would be more likely to experience cell death as the biofilm grew.

Figure adapted from Asally et al., "Localized cell death focuses mechanical forces during 3D patterning in a biofilm"

In synthetic biology, bacterial cell-cell communication has been used to genetically encode simple pattern formation and to synchronize oscillations, among many others. These papers show that even in the simplest multicellular systems, the interplay of biological, chemical, and mechanical forces can create beautiful, complex patterns.

EDIT: Check out Lab Rat’s great post about this paper too!

Christina Agapakis About the Author: Christina Agapakis is a biological designer who blogs about biology, engineering, engineering biology, and biologically inspired engineering. Follow on Twitter @thisischristina.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. TikiCosmonaut 1:58 pm 06/9/2013


    Link to this
  2. 2. rloldershaw 9:10 pm 06/9/2013

    If anyone would like to see a brief review of about 80 examples of fractal self-similarity manifesting itself everywhere in nature from subatomic to galactic scales, go to:

    and see Paper #14 on the “Selected Papers” page.

    Robert L. Oldershaw
    Discrete Scale Relativity/Fractal Cosmology

    Link to this

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