Identification of a outer membrane porin required for intracellular replication.

is a gram-negative, obligate intracellular pathogen that causes human Q fever. Within host cells, proliferates in a spacious, acidic, lysosome-derived -containing vacuole (CCV) by a process that requires the Dot/Icm type IVB secretion system to deliver effectors that manipulate host cell functions. A previous transposon mutagenesis screen identified the gene as being important for intracellular replication of . Here, the function of Cbu0937 was investigated. The ::Tn mutant had no detectable defect replicating in the axenic acidified citrate cysteine medium 2. Additionally, intracellular replication of the ::Tn mutant was not restored by co-infection of host cells with an isogenic wild-type strain of . Thus, the ::Tn mutant has a cell-intrinsic intracellular replication defect. Intracellular replication of the ::Tn mutant was restored by complementing the gene with a plasmid encoding either untagged or an epitope-tagged version of Cbu0937. Analysis of the predicted structure of the Cbu0937 protein using AlphaFold revealed high similarity between Cbu0937 and several bacterial porins. Fractionation studies and surface labeling of producing a functional epitope-tagged protein indicated the localization of Cbu0937 to the bacterial outer membrane. From these data, we conclude that encodes a porin that plays an essential role in supporting intracellular replication, which likely involves the acquisition of an important metabolite in the CCV lumen.