DcaP-family porins are required for carboxylic acid utilization and infection in Acinetobacter baumannii

Acinetobacter baumannii is a pathogen of concern and a leading cause of multidrug-resistant healthcare-associated infections. The A. baumannii outer membrane is a barrier to antimicrobials and host defenses but must also allow essential nutrients to permeate. Here, we investigate the functional importance of the putative DcaP-family outer membrane porins, which include a proposed vaccine target in A. baumannii. All A. baumannii genomes surveyed encode multiple DcaP family porins, which we classify in four classes based on protein sequence phylogeny (DcaP1-4). DcaP proteins encoded by species in other genera could not be mapped to these DcaP classes and phylogenetic analysis suggests DcaP1-4 proteins diversified within Acinetobacter. Phenotypic array assays and additional experiments show that the DcaP proteins were necessary for growth on multiple di- and tri-carboxylic acids as sole carbon sources, including citric acid and tricarballylic acid. Specifically, DcaP3 was required; however, DcaP1, DcaP2, and DcaP4 were all able to complement the total dcaP knockout to varying degrees, suggesting partial functional overlap. Finally, a mutant lacking all DcaP proteins was attenuated in the liver and spleen in a mouse model of bloodstream infection and complemented by expression of DcaP3. However, a ∆dcaP3 mutant had no defect, demonstrating functional redundancy among DcaP proteins during infection. These findings provide insight on how A. baumannii acquires nutrients through the outer membrane barrier and show DcaP proteins are important during infection in specific host niches, validating their potential as a therapeutic target.