Characterization of Acinetobacter baumannii core oligosaccharide synthesis reveals novel aspects of lipooligosaccharide assembly

• Published in: mBio 2024-03, Vol.15 (3), p.e0301323-e0301323
• Main Authors: VanOtterloo, Leah M, Macias, Luis A, Powers, Matthew J, Brodbelt, Jennifer S, Trent, M Stephen
• Format: Article
• Language: English
• Subjects: Bacteriology; Kdo; lipooligosaccharide; lipopolysaccharide; LOS; LPS; outer membrane; Research Article
• ISSN: 2150-7511; 2150-7511
• DOI: 10.1128/mbio.03013-23

A fundamental feature of Gram-negative bacteria is their outer membrane that protects the cell against environmental stressors. This defense is predominantly due to its asymmetry, with glycerophospholipids located in the inner leaflet and lipopolysaccharide (LPS) or lipooligosaccharide (LOS) confined to the outer leaflet. LPS consists of a lipid A anchor, a core oligosaccharide, and a distal O-antigen while LOS lacks O-antigen. While LPS/LOS is typically essential for growth, this is not the case for . Despite this unique property, the synthesis of the core oligosaccharide of LOS is not well-described. Here, we characterized the LOS chemotypes of strains with mutations in a predicted core oligosaccharide locus via tandem mass spectrometry. This allowed for an extensive identification of genes required for core assembly that can be exploited to generate precise structural LOS modifications in many strains. We further investigated two chemotypically identical yet phenotypically distinct mutants, ∆ and ∆ , that exposed a possible link between LOS and the peptidoglycan cell wall-two cell envelope components whose coordination has not yet been described in . Selective reconstruction of the core oligosaccharide via expression of 2903 and LpsB revealed that these proteins rely on each other for the unusual tandem transfer of two residues, KdoIII and N-acetylglucosaminuronic acid. The data presented not only allow for better usage of as a tool to study outer membrane integrity but also provide further evidence for a novel mechanism of core oligosaccharide assembly.IMPORTANCE is a multidrug-resistant pathogen that produces lipooligosaccharide (LOS), a glycolipid that confers protective asymmetry to the bacterial outer membrane. The core oligosaccharide is a ubiquitous component of LOS that typically follows a well-established model of synthesis. In addition to providing an extensive analysis of the genes involved in the synthesis of the core region, we demonstrate that this organism has evidently diverged from the long-held archetype of core synthesis. Moreover, our data suggest that LOS assembly is important for cell division and likely intersects with the synthesis of the peptidoglycan cell wall, another essential component of the Gram-negative cell envelope. This connection between LOS and cell wall synthesis provides an intriguing foundation for a unique method of outer membrane biogenesis and cell envelope coordination.