Confinement Discerns Swarmers from Planktonic Bacteria

Abstract

Powered by flagella, many species of bacteria exhibit collective motion on a solid surface commonly known as swarming. Physical changes like cell elongation and hyper flagellation have been shown to accompany swarming phenotype. Less noticeable, however, are the contrasts of collective motion between the swarming cells and the planktonic cells of comparable cell density. Here, we show that when confined by microwells of specific sizes mounted on a soft agar surface, novel bacteria Enterobacter sp. SM3 under swarming condition exhibited “single-swirl” motion pattern distinct from “multi-swirl” motion pattern formed by its concentrated planktonic counterpart. We hypothesize that “rafting behavior” of the swarming bacteria upon dilution might account for the motion pattern difference. This was further validated through computational simulation where swarming cells are modeled by lower repulsion and stronger alignment among them than planktonic cells. Our new technical approach also enabled us to observe swarming on a non-agar tissue surface.

Biofilm and swarming emergent behaviours controlled through the aid of biophysical understanding and tools

“…Spatial confinement is another physical approach for inducing dynamic cell-density patterns, such as vortexes. A theoretical model of active fluidics has suggested that the confinement geometry could result in dynamic patterns, including vortex lattices [ 70 , 71 ]. While a detailed analysis is yet to be done, a similar pattern has been observed in swarming B. subtilis in a meniscus open channel, named MeniFluidics [ 72 ].…”

“…Increasing cell densities enhance bacteria motility [18,50] Inhomogeneous cell density patterns of living and dead cells shape biofilm's wrinkle architecture [58] and EPS production is thickness dependent [60] Light Light drives bulk swarm motility in phototactic bacteria and blue light can slow down cells and lead to local cell accumulation [65,66] Blue light can be used to pattern biofilms in genetically engineered cells or to induce biofilm dispersal through cell hyperpolarization [74][75][76][77]79] Mechanical patterning Geometric confinement induces vortex patterns useful to identify swarming motility [70,71] 3D printing and Menifluidics can direct biofilm growth with submillimetre precision [72,[81][82][83]…”