  Optical tweezers are a versatile tool that can be used to manipulate small
particles including both motile and non-motile bacteria and cells. The
orientation of a non-spherical particle within a beam depends on the shape of
the particle and the shape of the light field. By using multiple beams,
sculpted light fields or dynamically changing beams, it is possible to control
the orientation of certain particles. In this paper we discuss the orientation
of the rod-shaped bacteria Escherichia coli (E. coli) using dynamically
shifting annular beam optical tweezers. We begin with examples of different
beams used for the orientation of rod-shaped particles. We discuss the
differences between orientation of motile and non-motile particles, and explore
annular beams and the circumstances when they may be beneficial for
manipulation of non-spherical particles or cells. Using simulations we map out
the trajectory the E. coli takes. Estimating the trap stiffness along the
trajectory gives us an insight into how stable an intermediate rotation is with
respect to the desired orientation. Using this method, we predict and
experimentally verify the change in the orientation of motile E. coli from
vertical to near-horizontal with only one intermediate step. The method is not
specific to exploring the orientation of particles and could be easily extended
to quantify the stability of an arbitrary particle trajectory.
