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Characterization of an Acinetobacter baumannii lptD deletion strain: Permeability defects and response to inhibition of lipopolysaccharide and fatty acid biosynthesis

Bojkovic, Jade and Richie, Daryl and Six, David and Rath, Christopher and Sawyer, William and Hu, Daniel and Dean, Charles (2016) Characterization of an Acinetobacter baumannii lptD deletion strain: Permeability defects and response to inhibition of lipopolysaccharide and fatty acid biosynthesis. Journal of Bacteriology, 198 (4). pp. 731-741. ISSN 1098-5530

Abstract

Lipid A on the Gram-negative outer membrane (OM) is synthesized in the cytoplasm by the Lpx pathway and translocated to the OM by the Lpt pathway. Some Acinetobacter baumannii strains can tolerate the complete loss of lipopolysaccharide (LPS) resulting from the inactivation of early LPS pathway genes such as lpxC. Here, we characterized a mutant deleted for lptD, which encodes anOMprotein that mediates the final translocation of fully synthesized LPS to the OM. Cells lacking lptD had a growth defect comparable to that of an lpxC deletion mutant under the growth conditions tested but were more sensitive to hydrophobic antibiotics, revealing a more significant impact on cell permeability from impaired LPS translocation than from the loss of LPS synthesis. Consistent with this, ATP leakage and N-phenyl-1-naphthylamine (NPN) fluorescence assays indicated a more severe impact of lptD deletion than of lpxC deletion on inner and outer membrane permeability, respectively. Targeted liquid chromatography-mass spectrometry (LCMS) analysis of LPS intermediates from UDP-3-O-R-3-hydroxylauroyl-N-acetyl-α-Dglucosamine through lipid IVA showed that the loss of LptD caused an accumulation of lipid IVA. This suggested that pathway intermediate accumulation or mislocalization caused by the blockage of later LPS pathway steps impacts envelope integrity. Supporting this notion, chemical inhibition of lipid A precursor enzymes, including LpxC and FabB/F, in the lptD deletion strain partially rescued growth and permeability defects.

Item Type: Article
Date Deposited: 10 Mar 2018 00:45
Last Modified: 25 Jan 2019 00:45
URI: https://oak.novartis.com/id/eprint/26294

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