Encapsulated bacteria deform lipid vesicles into flagellated swimmers

Abstract

We study a synthetic system of motile Escherichia coli bacteria encapsulated inside giant lipid vesicles. Forces exerted by the bacteria on the inner side of the membrane are sufficient to extrude membrane tubes filled with one or several bacteria. We show that a physical coupling between the membrane tube and the flagella of the enclosed cells transforms the tube into an effective helical flagellum propelling the vesicle. We develop a simple theoretical model to estimate the propulsive force from the speed of the vesicles and demonstrate the good efficiency of this coupling mechanism. Together, these results point to design principles for conferring motility to synthetic cells.

Dynamic shapes of floppy vesicles enclosing active Brownian particles with membrane adhesion

“…15,16 In many other examples, biological materials are combined with active synthetic constituents with a hope to mimic various biological systems or even go beyond their functionality. 17,18 Here, an interesting example is a closed membrane enclosing biological micro-swimmers such as bacteria [19][20][21] or synthetic self-propelled particles. 18,[22][23][24][25] Active components inside the soft confinement exert forces on the surface, leading to highly dynamic non-equilibrium shape changes which resemble certain processes in living cells such as the formation of filopodia and lamellipodia, 5,26,27 and active shape fluctuations of the membrane.…”

“…For instance, swimming bacteria or motile synthetic particles within a vesicle induce the formation of tethers and protrusions which dynamically elongate and retract. [18][19][20] In equilibrium, string-of-pearls-like and tubular protrusions can be formed by amphipathic peptides or BAR domain proteins, 32,33 but these structures are static and correspond to a minimum of total energy. Therefore, different physical mechanisms govern the formation of various membrane structures in equilibrium and in non-equilibrium active vesicles.…”

Dynamic shapes of floppy vesicles enclosing active Brownian particles with membrane adhesion

“…In many other examples, biological materials are combined with active synthetic constituents with a hope to mimic various biological systems or even go beyond their functionality [17,18]. Here, an interesting example is a closed membrane enclosing biological micro-swimmers such as bacteria [19][20][21] or synthetic self-propelled particles [18,[22][23][24][25]. Active components inside the soft confinement exert forces on the surface, leading to highly dynamic nonequilibrium shape changes which resemble certain processes in living cells such as the formation of filopodia and lamellipodia [5,26,27], and active shape fluctuations of the membrane [28][29][30].…”

“…The main features that differentiate active vesicles from various membrane structures in equilibrium [31,32] are active force generation due to the enclosed active components and dynamic shape changes of the membrane. For instance, swimming bacteria or motile synthetic particles within a vesicle induce the formation of tethers and protrusions which dynamically elongate and retract [18][19][20]. In equilibrium, string-of-pearls-like and tubular protrusions can be formed by amphipathic peptides or BAR domain proteins [32,33], but these structures are static and correspond to a minimum of total energy.…”

Janus magnetoelastic membrane swimmers

“…60,61 Interestingly, diverse polyhedral shapes have been reported in membranes with build-in 62 or chemical-reaction-induced 63 heterogeneous elasticity. Recently, body deformations also have been accomplished in lipid vesicles by extruding the membrane with encapsulated bacteria 64,65 or active particles. 66,67 In this article, we computationally investigate the propulsion mechanism of Janus magnetoelastic crystalline membrane microswimmers that are actuated by a time-varying magnetic field.…”