A Survey of Two-Component Systems in Coxiella burnetii Reveals Redundant Regulatory Schemes and a Requirement for an Atypical PhoBR System in Mammalian Cell Infection

C. burnetii is an obligate intracellular bacterium with a spore-like stability allowing it to survive long periods of time in the environment. This stability is likely due to its biphasic developmental cycle, whereby it can transition from an environmentally stable small-cell variant (SCV) to a metabolically active large-cell variant (LCV).