4.5 Bacterial Circus Arena
81
the stack negatively charged (Fig. 4.22b). The nematic order of these elongated
aggregates is enhanced at lower temperatures, when the stacks grow longer. The
experiments are carried out in a shallow cuvette where nematic order can be set by
rubbing the confining plates (Fig. 4.22c).
a
b
z
c
Fig. 4.22 (a) The structure of an LCLC unit.
The acidic group is colored magenta, and sodium
atoms, pink. (b) Nematic stacks. Small circles
show sodium ions. (c) Sketch of the experimental
setup, showing the director and a moving bacterium
(Zhou, 2017)
Lavrentovich and coworkers have
taken advantage of this medium to explore interactions of bacterial suspensions with liquid-crystalline patterns
in what they call living liquid crystals, setting the aim of controlling the
chaotic behavior of bacterial suspensions (Zhou et al, 2014; Peng et al,
2016). When rod-like B. subtilis cells
are dispersed in a liquid crystalline environment with spatially varying orientation, they tend to align with the
director and move along these lines in
either direction. At the same time, they
recognize subtle details in liquid crystal patterns. This makes it possible to
control the distribution of bacteria and
the geometry of their trajectories by arranging nematic alignment patterns, which can be created on demand by anchoring
the nematic director with the help of a light-sensitive lithographic design of confining
plates (Guo et al, 2016). In this way, it is possible, for example, to arrange a periodic
pattern of defects that induces bacteria to self-organize into a lattice of co-rotating
vortices (Peng et al, 2016).
Interactions between nematic and bacterial alignments are mutual. While bacteria
orient along the director, the nematic order is distorted by their activity (Fig. 4.23b),
leading eventually to nucleation of paired defects (Fig. 4.23c). Bacteria differentiate
between topological defects, heading toward defects of positive topological charge
and avoiding those of negative charge. This is seen in both experimental (Fig. 4.24b)
a
a
a
b
a
c
Fig. 4.23 (a) Inactive bacteria (highlighted by ellipses) in an ordered nematic align along the
director. (b) Active bacteria distort nematic order. (c) Nucleating positive (semicircles) and negative
(triangles) half-charged defects. Yellow dashes show bacterial orientation (Zhou, 2017)
81
the stack negatively charged (Fig. 4.22b). The nematic order of these elongated
aggregates is enhanced at lower temperatures, when the stacks grow longer. The
experiments are carried out in a shallow cuvette where nematic order can be set by
rubbing the confining plates (Fig. 4.22c).
a
b
z
c
Fig. 4.22 (a) The structure of an LCLC unit.
The acidic group is colored magenta, and sodium
atoms, pink. (b) Nematic stacks. Small circles
show sodium ions. (c) Sketch of the experimental
setup, showing the director and a moving bacterium
(Zhou, 2017)
Lavrentovich and coworkers have
taken advantage of this medium to explore interactions of bacterial suspensions with liquid-crystalline patterns
in what they call living liquid crystals, setting the aim of controlling the
chaotic behavior of bacterial suspensions (Zhou et al, 2014; Peng et al,
2016). When rod-like B. subtilis cells
are dispersed in a liquid crystalline environment with spatially varying orientation, they tend to align with the
director and move along these lines in
either direction. At the same time, they
recognize subtle details in liquid crystal patterns. This makes it possible to
control the distribution of bacteria and
the geometry of their trajectories by arranging nematic alignment patterns, which can be created on demand by anchoring
the nematic director with the help of a light-sensitive lithographic design of confining
plates (Guo et al, 2016). In this way, it is possible, for example, to arrange a periodic
pattern of defects that induces bacteria to self-organize into a lattice of co-rotating
vortices (Peng et al, 2016).
Interactions between nematic and bacterial alignments are mutual. While bacteria
orient along the director, the nematic order is distorted by their activity (Fig. 4.23b),
leading eventually to nucleation of paired defects (Fig. 4.23c). Bacteria differentiate
between topological defects, heading toward defects of positive topological charge
and avoiding those of negative charge. This is seen in both experimental (Fig. 4.24b)
a
a
a
b
a
c
Fig. 4.23 (a) Inactive bacteria (highlighted by ellipses) in an ordered nematic align along the
director. (b) Active bacteria distort nematic order. (c) Nucleating positive (semicircles) and negative
(triangles) half-charged defects. Yellow dashes show bacterial orientation (Zhou, 2017)