  We report the selective stabilization of chiral rotational direction of
bacterial vortices, from turbulent bacterial suspension, in achiral circular
microwells sealed by an oil-water interface. This broken-symmetry, originating
from the intrinsic chirality of bacterial swimming near hydrodynamically
different top and bottom surfaces, generates a chiral edge current of bacteria
at lateral boundary and grows stronger as bacterial density increases. We
demonstrate that chiral edge current favors co-rotational configurations of
interacting vortices, enhancing their ordering. The interplay between the
intrinsic chirality of bacteria and the geometric properties of the boundary is
a key-feature for the pairing order transition of active turbulence.
