The human pathogen Coxiella burnetii is the causative agent of Q fever, a febrile illness which can cause a serious chronic infection. Coxiella is a unique Gram negative intracellular bacterium that replicates within host cell lysosome-derived vacuoles. The molecular mechanisms utilised by Coxiella to facilitate success within this normally hostile compartment are unknown. In a previous study, a transposon mutagenesis screen revealed that disruption of the gene encoding the novel protein CBU2072 renders Coxiella incapable of intracellular replication. We have demonstrated that genetic complementation, with plasmid encoded cbu2072, restores the ability of the transposon mutant to replicate inside host cells, confirming that CBU2072 is essential for intracellular replication of Coxiella. Through further complementation experiments, using truncated and site-directed mutations of CBU2072, several important regions of this protein have been identified. Interestingly, when the cbu2072 mutant coinhabits a replicative vacuole with either wild type Coxiella or Leishmania mexicana during coinfection experiments, intracellular replication of the transposon mutant is restored. In addition, CBU2072 has low homology to pyridine nucleotide transhydrogenases, which are involved in regulating the balance between NAD(H) and NADP(H). These observations indicate that CBU2072 may modulate the environment within the replicative vacuole, possibly influencing redox balance to support replication. CBU2072 is not translocated through the essential Dot/Icm Type IV secretion system encoded by Coxiella. However, our current studies are investigating the localisation of CBU2072 during infection, with preliminary data suggesting that it may be secreted into the replicative vacuole. Functional characterisation of CBU2072 aims to elucidate the mechanisms utilised by Coxiella burnetii to replicate inside the phagolysosomal environment within human host cells.