  We characterize the full spatiotemporal gait of populations of swimming {\it
Escherichia coli} using renewal processes to analyze the measurements of
intermediate scattering functions. This allows us to demonstrate quantitatively
how the persistence length of an engineered strain can be controlled by a
chemical inducer and to report a controlled transition from perpetual tumbling
to smooth swimming. For wild-type {\it E.~coli}, we measure simultaneously the
microscopic motility parameters and the large-scale effective diffusivity,
hence quantitatively bridging for the first time small-scale directed swimming
and macroscopic diffusion.
