Interaction of Pf4 tactoids with bacteria and synthetic colloidal rods.

We investigated the interaction of liquid crystal droplets, formed by a phase separating system of elongated virus particles and polymer with rod-like impurities. The virus particles were Pf4, which when mixed with sodium alginate as polymer, phase separated into an isotropic phase in coexistence with a nematic phase of the virus particles. The nematic phase appeared in the form of spindle-shaped liquid crystal droplets, which are called tactoids. We studied the interaction of this mixture with micrometer sized rods, which were either bacteria (Bacillus subtilis or Escherichia coli) or inert colloidal particles (made of SU8 photoresist polymer or silica). Confocal laser scanning microscopy was used to examine the mixtures and four different dominant configurations were found, classified as no attachment, partial attachment of the rod to the tactoid, a "sandwich" state, where two tactoids interact with the same rod, and lastly encapsulation of the rods by the tactoids. We categorized the results in terms of surface properties and rod geometry (size and aspect ratio). We further investigated the system through numerical calculation in a simplified two-dimensional model. Finally, we addressed the role of confining the experimental system from three dimensions to a quasi two-dimensional setup, a relevant scenario in bacteria biofilms.