The Mla pathway in Acinetobacter baumannii has no demonstrable role in anterograde lipid transport

The asymmetric outer membrane (OM) of Gram-negative bacteria functions as a selective permeability barrier to the environment. Perturbations to OM lipid asymmetry sensitize the cell to antibiotics. As such, mechanisms involved in lipid asymmetry are fundamental to our understanding of OM lipid homeostasis. One such mechanism, the Maintenance of lipid asymmetry (Mla) pathway has been proposed to extract mislocalized glycerophospholipids from the outer leaflet of the OM and return them to the inner membrane (IM). Work on this pathway in Acinetobacter baumannii support conflicting models for the directionality of the Mla system being retrograde (OM to IM) or anterograde (IM to OM). Here, we show conclusively that A. baumannii mla mutants exhibit no defects in anterograde transport. Furthermore, we identify an allele of the GTPase obgE that is synthetically sick in the absence of Mla; providing another link between cell envelope homeostasis and stringent response.

[1]  Nicole P. Giordano,et al.  Separation of the Cell Envelope for Gram-negative Bacteria into Inner and Outer Membrane Fractions with Technical Adjustments for Acinetobacter baumannii. , 2020, Journal of visualized experiments : JoVE.

[2]  Aimee R. P. Tierney,et al.  Characterization of RelA in Acinetobacter baumannii , 2020, Journal of bacteriology.

[3]  J. Naismith,et al.  Porins and small-molecule translocation across the outer membrane of Gram-negative bacteria , 2019, Nature Reviews Microbiology.

[4]  Marcin Grabowicz,et al.  Countering Gram-Negative Antibiotic Resistance: Recent Progress in Disrupting the Outer Membrane with Novel Therapeutics , 2019, Antibiotics.

[5]  R. Losick,et al.  Robust Suppression of Lipopolysaccharide Deficiency in Acinetobacter baumannii by Growth in Minimal Medium , 2019, Journal of bacteriology.

[6]  M. Powers,et al.  Intermembrane transport: Glycerophospholipid homeostasis of the Gram-negative cell envelope , 2019, Proceedings of the National Academy of Sciences.

[7]  Gareth W. Hughes,et al.  Evidence for phospholipid export from the bacterial inner membrane by the Mla ABC transport system , 2019, Nature Microbiology.

[8]  M. Trent,et al.  Pushing the envelope: LPS modifications and their consequences , 2019, Nature Reviews Microbiology.

[9]  Xiongfeng Dai,et al.  (p)ppGpp: the magic governor of bacterial growth economy , 2019, Current Genetics.

[10]  Marcin Grabowicz.  Lipoproteins and Their Trafficking to the Outer Membrane , 2019, EcoSal Plus.

[11]  A. Jerse,et al.  Neisseria gonorrhoeae MlaA influences gonococcal virulence and membrane vesicle production , 2019, PLoS pathogens.

[12]  Shu-Sin Chng,et al.  Characterization of Interactions and Phospholipid Transfer between Substrate Binding Proteins of the OmpC-Mla System. , 2018, Biochemistry.

[13]  M. Powers,et al.  Isolation of Lipid Cell Envelope Components from Acinetobacter baumannii. , 2019, Methods in molecular biology.

[14]  M. Powers,et al.  RecET-Mediated Recombineering in Acinetobacter baumannii. , 2019, Methods in molecular biology.

[15]  M. Powers,et al.  Phospholipid retention in the absence of asymmetry strengthens the outer membrane permeability barrier to last-resort antibiotics , 2018, Proceedings of the National Academy of Sciences.

[16]  Samuel I. Miller,et al.  The Acinetobacter baumannii Mla system and glycerophospholipid transport to the outer membrane , 2018, bioRxiv.

[17]  B. Luisi,et al.  Multidrug efflux pumps: structure, function and regulation , 2018, Nature Reviews Microbiology.

[18]  M. Surette,et al.  The Mla Pathway Plays an Essential Role in the Intrinsic Resistance of Burkholderia cepacia Complex Species to Antimicrobials and Host Innate Components , 2018, Journal of bacteriology.

[19]  C. Ortiz-de-Solórzano,et al.  Modulation of Haemophilus influenzae interaction with hydrophobic molecules by the VacJ/MlaA lipoprotein impacts strongly on its interplay with the airways , 2018, Scientific Reports.

[20]  T. Silhavy,et al.  The Escherichia coli Phospholipase PldA Regulates Outer Membrane Homeostasis via Lipid Signaling , 2018, mBio.

[21]  M. Powers,et al.  Expanding the paradigm for the outer membrane: Acinetobacter baumannii in the absence of endotoxin , 2018, Molecular microbiology.

[22]  D. Bumann,et al.  Structural basis for maintenance of bacterial outer membrane lipid asymmetry , 2017, Nature Microbiology.

[23]  J. Mohr,et al.  The antibiotic pipeline: reviving research and development and speeding drugs to market , 2017, Expert review of anti-infective therapy.

[24]  R. Shrivastava,et al.  Outer membrane lipid homeostasis via retrograde phospholipid transport in Escherichia coli , 2017, bioRxiv.

[25]  I. Henderson,et al.  Architectures of Lipid Transport Systems for the Bacterial Outer Membrane , 2016, Cell.

[26]  B. Fox,et al.  The Power of Asymmetry: Architecture and Assembly of the Gram-Negative Outer Membrane Lipid Bilayer. , 2016, Annual review of microbiology.

[27]  M. Wenk,et al.  Defining key roles for auxiliary proteins in an ABC transporter that maintains bacterial outer membrane lipid asymmetry , 2016, eLife.

[28]  V. Nizet,et al.  Molecular dynamic study of MlaC protein in Gram‐negative bacteria: conformational flexibility, solvent effect and protein‐phospholipid binding , 2016, Protein science : a publication of the Protein Society.

[29]  David J. Sherman,et al.  Lipopolysaccharide transport and assembly at the outer membrane: the PEZ model , 2016, Nature Reviews Microbiology.

[30]  K. C. Huang,et al.  Disruption of lipid homeostasis in the Gram-negative cell envelope activates a novel cell death pathway , 2016, Proceedings of the National Academy of Sciences.

[31]  P. Kohl,et al.  A novel mechanism for the biogenesis of outer membrane vesicles in Gram-negative bacteria , 2016, Nature Communications.

[32]  Brent S. Weber,et al.  Pathogenic Acinetobacter: from the Cell Surface to Infinity and Beyond , 2015, Journal of bacteriology.

[33]  Z. Chong,et al.  Osmoporin OmpC forms a complex with MlaA to maintain outer membrane lipid asymmetry in Escherichia coli , 2015, Molecular microbiology.

[34]  Samuel I. Miller,et al.  Delivery of cardiolipins to the Salmonella outer membrane is necessary for survival within host tissues and virulence. , 2015, Cell host & microbe.

[35]  M. Feldman,et al.  Prokaryotic membrane vesicles: new insights on biogenesis and biological roles , 2015, Biological chemistry.

[36]  M. Trent,et al.  Defining Gene-Phenotype Relationships in Acinetobacter baumannii through One-Step Chromosomal Gene Inactivation , 2014, mBio.

[37]  C. Whitfield,et al.  Biosynthesis and export of bacterial lipopolysaccharides. , 2014, Annual review of biochemistry.

[38]  T. Silhavy,et al.  Assembly of Outer Membrane β-Barrel Proteins: the Bam Complex. , 2011, EcoSal Plus.

[39]  S. Lovett,et al.  The ObgE/CgtA GTPase influences the stringent response to amino acid starvation in Escherichia coli , 2009, Molecular microbiology.

[40]  T. Silhavy,et al.  An ABC transport system that maintains lipid asymmetry in the Gram-negative outer membrane , 2009, Proceedings of the National Academy of Sciences.

[41]  Samuel I. Miller,et al.  PhoPQ-Mediated Regulation Produces a More Robust Permeability Barrier in the Outer Membrane of Salmonella enterica Serovar Typhimurium , 2007, Journal of bacteriology.

[42]  S. M. Sullivan,et al.  The Escherichia coli GTPase CgtAE Cofractionates with the 50S Ribosomal Subunit and Interacts with SpoT, a ppGpp Synthetase/Hydrolase , 2004, Journal of bacteriology.

[43]  H. Nikaido.  Molecular Basis of Bacterial Outer Membrane Permeability Revisited , 2003, Microbiology and Molecular Biology Reviews.

[44]  J. W. Campbell,et al.  The Enigmatic Escherichia coli fadE Gene Is yafH , 2002, Journal of bacteriology.

[45]  K. H. Kalk,et al.  Structural evidence for dimerization-regulated activation of an integral membrane phospholipase , 1999, Nature.

[46]  J. Tommassen,et al.  Escherichia coli outer membrane phospholipase A: role of two serines in enzymatic activity. , 1996, Biochemistry.

[47]  R. Heath,et al.  Guanosine tetraphosphate inhibition of fatty acid and phospholipid synthesis in Escherichia coli is relieved by overexpression of glycerol-3-phosphate acyltransferase (plsB). , 1994, The Journal of biological chemistry.

[48]  H. Nikaido,et al.  Porins and specific diffusion channels in bacterial outer membranes. , 1994, The Journal of biological chemistry.

[49]  H. Bremer,et al.  Escherichia coli ppGpp synthetase II activity requires spoT. , 1991, The Journal of biological chemistry.

[50]  H. Nikaido,et al.  Asymmetric localization of lipopolysaccharides on the outer membrane of Salmonella typhimurium , 1980, Journal of bacteriology.

[51]  M. Schindler,et al.  Interaction of divalent cations and polymyxin B with lipopolysaccharide. , 1979, Biochemistry.

[52]  M. Osborn,et al.  Translocation of phospholipids between the outer and inner membranes of Salmonella typhimurium. , 1977, The Journal of biological chemistry.

[53]  C. Scandella,et al.  A membrane-bound phospholipase A1 purified from Escherichia coli. , 1971, Biochemistry.