Component of a regulatory phosphorelay system that controls B.abortus cell growth, division, and intracellular survival inside mammalian host cells. This signaling pathway is composed of CckA, ChpT, CtrA and CpdR. CckA autophosphorylates in the presence of ATP on a conserved His residue and transfers a phosphoryl group to a conserved Asp residue on its C-terminal receiver domain. CckA-P transfers phosphoryl groups to the ChpT phosphotransferase. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. This gene cannot be deleted or disrupted in the absence of a complementary copy expressed in trans, indicating this gene is essential in B.abortus.