Enhancement in the diffusivity of Brownian spheroids in the presence of spheres

Run-and-tumble kinematics of Enterobacter Sp. SM3

The recent discovery of the peritrichous, swarm-competent bacterium Enterobacter sp. SM3 has offered a new opportunity to investigate the connection between bacterial swimming and swarming. Here, we report the run-and-tumble behavior of SM3 as planktonic swimming cells and as swarming cells diluted in liquid medium, drawing comparison between the two states. Swimming cells of SM3 run for an average of 0.77 s with a speed of approximately 30µm/s before tumbling. Tumbles last for a duration of 0.12 s on average and cause changes in direction averaging 69^{∘}. Swimming cells exposed to the common chemoattractant serine in bulk solution suppress the frequency of tumbles in the steady state, lengthening the average run duration and decreasing the average tumble angle. When exposed to aspartate, cells do not demonstrate a notable change in run-and-tumble parameters in the steady state. For swarming cells of SM3, the frequency of tumbles is reduced, with the average run duration being 50% longer on average than that of swimming cells in the same liquid medium. Additionally, the average tumble angle of swarming cells is smaller by 35%. These findings reveal that the newly identified species, SM3, performs run-and-tumble motility similar to other species of peritrichous bacteria such as E. coli, both in the swimming and swarming states. We present a simple mechanical model, which provides a physical understanding of the run-and-tumble behavior of peritrichous bacteria.

Breaking the size constraint for nano cages using annular patchy particles

Engineering structures like nanocages, shells, and containers, by self-assembly of colloids is a challenging problem. One of the main challenges is to define the shape of the individual subunits to control the radius of the closed shell structures. In this work, we have proposed a simple model for the subunit, which comprises a spheroidal or spherical hardcore decorated with an annular patch. The self-assembly of these building blocks leads to the formation of monodispersed spherical cages (close shells) or containers (curved clusters). For a spheroid with a given bonding range, the curvature of the shell is analytically related to only the patch angle of the building blocks and independent of the shape of the subunits. This model with only one control parameter can be used to engineer cages with the desired radius, which also have been verified using thermodynamic calculations. In the phase diagram of the system, 4 phases are identified which includes gas, closed shell, partially closed (containers) shell and percolated structures. When the diameters of the spherical cages formed are small, we observe an icosahedral symmetry similar to virus capsids. We also observed that the kinetics of the cage formation is very similar to the nucleation and growth kinetics of viruses and is the key factor in determining the yield of closed shells.