Uncovering Mechanisms of Cell Envelope Integrity and Nutrient Acquisition in Acinetobacter baumannii

Acinetobacter baumannii is an emerging bacterial pathogen of critical concern due to increasing multidrug resistance. The outer membrane (OM) of A. baumannii is a key barrier to antimicrobials and stressors but must also allow the entry of essential nutrients. The maintenance of lipid asymmetry (Mla) system is the primary homeostatic mechanism in Gram-negative bacteria to maintain lipid asymmetry by removing mislocalized phospholipids from the OM. In A. baumannii and other bacteria, loss of the Mla system results in increased sensitivity to membrane stressors and some antibiotics as well as attenuated virulence. In A. baumannii lacking the Mla system, we show that the cellular levels of the essential glycan carrier undecaprenyl phosphate (Und-P) are critically important for maintaining cell envelope integrity and promoting pathogenicity. In an independent study, we characterize a family of OM porins required for growth on carboxylates. The dicarboxylic acid porin (DcaP) was putatively assigned dicarboxylate specificity based on genomic context. We show that major A. baumannii vaccine candidate DcaP3 is important for growth on tricarboxylates and dicarboxylates as sole carbon sources including the citric acid cycle intermediate, citrate. Loss of DcaP3 resulted in reduced bacterial burden from the liver and spleen of mice, suggesting one of the DcaP3-associated carbon sources is important during infection. Altogether, this thesis uncovers synergy between the Mla system and Und-P that is important for cell envelope integrity and characterizes a family of porins critical for nutrient acquisition in the bacterial pathogen A. baumannii.