  Active matter exhibits remarkable collective behavior in which flows,
continuously generated by active particles, are intertwined with the
orientational order of these particles. The relationship remains poorly
understood as the activity and order are difficult to control independently.
Here we demonstrate important facets of this interplay by exploring dynamics of
swimming bacteria in a liquid crystalline environment with pre-designed
periodic splay and bend in molecular orientation. The bacteria are expelled
from the bend regions and condense into polar jets that propagate and transport
cargo unidirectionally along the splay regions. The bacterial jets remain
stable even when the local concentration exceeds the threshold of bending
instability in a non-patterned system. Collective polar propulsion and
different role of bend and splay are explained by an advection-diffusion model
and by numerical simulations that treat the system as a two-phase active
nematic. The ability of prepatterned liquid crystalline medium to streamline
the chaotic movements of swimming bacteria into polar jets that can carry cargo
along a predesigned trajectory opens the door for potential applications in
cell sorting, microscale delivery and soft microrobotics.
