The hybrid histidine kinase Hk1 is part of a two-component system that is essential for survival of Borrelia burgdorferi in feeding Ixodes scapularis ticks.

Two-component systems (TCS) are principal mechanisms by which bacteria adapt to their surroundings. Borrelia burgdorferi encodes only two TCS. One is comprised of a histidine kinase, Hk2, and the response regulator Rrp2.