Fast-Moving Bacteria Self-Organize into Active Two-Dimensional Crystals of Rotating Cells

Abstract

We investigate a new form of collective dynamics displayed by Thiovulum majus, one of the fastest-swimming bacteria known. Cells spontaneously organize on a surface into a visually striking two-dimensional hexagonal lattice of rotating cells. As each constituent cell rotates its flagella, it creates a tornadolike flow that pulls neighboring cells towards and around it. As cells rotate against their neighbors, they exert forces on one another, causing the crystal to rotate and cells to reorganize. We show how these dynamics arise from hydrodynamic and steric interactions between cells. We derive the equations of motion for a crystal, show that this model explains several aspects of the observed dynamics, and discuss the stability of these active crystals.

Shape control and compartmentalization in active colloidal cells

“…Crystallization has recently been observed in rotating magnetic Janus colloids (49) and fast-moving bacteria (50). Spinners in the interior of the cell resemble molecular motors that push themselves forward on their neighbors and, thus, sustain convective dynamics.…”

Motility in the epsilon-proteobacteria

“…It is also thought that high torque and the 62 largecell sizecontributes to self-organization of Thiovulumcells into 2D hexagonal lattices on surfaces which 63 may contribute to increased nutrient flux [23]. Although other epsilon-proteobacteria have not been studied 64 in similar detail, their ability to swimming through viscous media, and prevalent observations of rapid, 65 darting motility, suggest similar mechanisms underly the characteristic swimming ability of all epsilon-66 proteobacteria ( Figure 1).…”

“…Motility is also clearly important for environmental members 41 of the epsilon-proteobacteria as demonstrated by high expression levels of flagellar genes in hydrothermal 42 vent epsilon-proteobacteria [20,22]. In environmental Thiovulumspp., flagella play key roles in nutrient 43 acquisition whereby cells attach to surfaces and rotate their flagella to increase oxygen and sulphide flux for 44 metabolism [23]. 45 Despite using homologous flagellar systems, there are striking differences between epsilon-proteobacterial 46 and the enteric motility models Escherichia coli and Salmonella entericasv.…”

“…C. jejuni and 21 relatedspeciesare leading causes of gastroenteritis, yet often harmless commensals of birds [2]. Other 22 members of order Campylobacteralesare also associated with mammalian intestinal tracts, 23 includingWolinellasuccinogenes, a cattle rumen commensal [3], and pathogenic Arcobacterspecies [4]. 24 Helicobacter species are invariably digestive tract-associated, with H.pylori colonizing 50% of humans on 25 the planetand although associated with gastritis, gastric ulcers and gastric carcinoma, is also associated with 26 beneficial outcomes with gastroesophageal reflux and asthma, indicating that the relationship between 27 human host and H. pylori are more complex than first thought [5][6][7].…”

Active particle aggregate on complex bubble surfaces

“…[5] A model of e-coli bacteria for instance can be considered having motility and chirality. [6] Active particles have inherent energy (such as pulling water in and pushing out by squeezing) hence system can not be considered an equilibrium statistical system.…”