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Pushing the envelope: LPS modifications and their consequences


The defining feature of the Gram-negative cell envelope is the presence of two cellular membranes, with the specialized glycolipid lipopolysaccharide (LPS) exclusively found on the surface of the outer membrane. The surface layer of LPS contributes to the stringent permeability properties of the outer membrane, which is particularly resistant to permeation of many toxic compounds, including antibiotics. As a common surface antigen, LPS is recognized by host immune cells, which mount defences to clear pathogenic bacteria. To alter properties of the outer membrane or evade the host immune response, Gram-negative bacteria chemically modify LPS in a wide variety of ways. Here, we review key features and physiological consequences of LPS biogenesis and modifications.

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  1. 1.

    Muhlradt, P. F. & Golecki, J. R. Asymmetrical distribution and artifactual reorientation of lipopolysaccharide in the outer membrane bilayer of Salmonella typhimurium. Eur. J. Biochem. 51, 343–352 (1975).

  2. 2.

    Nikaido, H. & Vaara, M. Molecular basis of bacterial outer membrane permeability. Microbiol. Rev. 49, 1–32 (1985).

  3. 3.

    Whitfield, C. & Trent, M. S. Biosynthesis and export of bacterial lipopolysaccharides. Annu. Rev. Biochem. 83, 99–128 (2014).

  4. 4.

    Muhlradt, P. F., Menzel, J., Golecki, J. R. & Speth, V. Outer membrane of Salmonella. Sites of export of newly synthesised lipopolysaccharide on the bacterial surface. Eur. J. Biochem. 35, 471–481 (1973).

  5. 5.

    Osborn, M. J., Gander, J. E. & Parisi, E. Mechanism of assembly of the outer membrane of Salmonella typhimurium. Site of synthesis of lipopolysaccharide. J. Biol. Chem. 247, 3973–3986 (1972).

  6. 6.

    Young, H. E. et al. Discovery of the elusive UDP-diacylglucosamine hydrolase in the lipid A biosynthetic pathway in Chlamydia trachomatis. mBio 7, e00090 (2016).

  7. 7.

    Rubin, E. J., O’Brien, J. P., Ivanov, P. L., Brodbelt, J. S. & Trent, M. S. Identification of a broad family of lipid A late acyltransferases with non-canonical substrate specificity. Mol. Microbiol. 91, 887–899 (2014).

  8. 8.

    Hankins, J. V. et al. Elucidation of a novel Vibrio cholerae lipid A secondary hydroxy-acyltransferase and its role in innate immune recognition. Mol. Microbiol. 81, 1313–1329 (2011).

  9. 9.

    Okuda, S., Sherman, D. J., Silhavy, T. J., Ruiz, N. & Kahne, D. Lipopolysaccharide transport and assembly at the outer membrane: the PEZ model. Nat. Rev. Microbiol. 14, 337–345 (2016).

  10. 10.

    Sweet, C. R. et al. Enzymatic synthesis of lipid A molecules with four amide-linked acyl chains. LpxA acyltransferases selective for an analog of UDP-N-acetylglucosamine in which an amine replaces the 3”-hydroxyl group. J. Biol. Chem. 279, 25411–25419 (2004).

  11. 11.

    van Mourik, A. et al. Altered linkage of hydroxyacyl chains in lipid A of Campylobacter jejuni reduces TLR4 activation and antimicrobial resistance. J. Biol. Chem. 285, 15828–15836 (2010).

  12. 12.

    Gattis, S. G., Chung, H. S., Trent, M. S. & Raetz, C. R. The origin of 8-amino-3,8-dideoxy-D-manno-octulosonic acid (Kdo8N) in the lipopolysaccharide of Shewanella oneidensis. J. Biol. Chem. 288, 9216–9225 (2013).

  13. 13.

    Belunis, C. J. & Raetz, C. R. Biosynthesis of endotoxins. Purification and catalytic properties of 3-deoxy-D-manno-octulosonic acid transferase from Escherichia coli. J. Biol. Chem. 267, 9988–9997 (1992).

  14. 14.

    Hankins, J. V. & Trent, M. S. Secondary acylation of Vibrio cholerae lipopolysaccharide requires phosphorylation of Kdo. J. Biol. Chem. 284, 25804–25812 (2009).

  15. 15.

    Lobau, S., Mamat, U., Brabetz, W. & Brade, H. Molecular cloning, sequence analysis, and functional characterization of the lipopolysaccharide biosynthetic gene kdtA encoding 3-deoxy-α-D-manno-octulosonic acid transferase of Chlamydia pneumoniae strain TW-183. Mol. Microbiol. 18, 391–399 (1995).

  16. 16.

    Mamat, U., Baumann, M., Schmidt, G. & Brade, H. The genus-specific lipopolysaccharide epitope of Chlamydia is assembled in C. psittaci and C. trachomatis by glycosyltransferases of low homology. Mol. Microbiol. 10, 935–941 (1993).

  17. 17.

    Chung, H. S. & Raetz, C. R. Dioxygenases in Burkholderia ambifaria and Yersinia pestis that hydroxylate the outer Kdo unit of lipopolysaccharide. Proc. Natl Acad. Sci. USA 108, 510–515 (2011).

  18. 18.

    White, K. A., Lin, S., Cotter, R. J. & Raetz, C. R. A. Haemophilus influenzae gene that encodes a membrane bound 3-deoxy-D-manno-octulosonic acid (Kdo) kinase. Possible involvement of Kdo phosphorylation in bacterial virulence. J. Biol. Chem. 274, 31391–31400 (1999).

  19. 19.

    Boll, J. M. et al. Reinforcing lipid A acylation on the cell surface of Acinetobacter baumannii promotes cationic antimicrobial peptide resistance and desiccation survival. mBio 6, e00478–15 (2015). This study identified secondary acyltransferases in A. baumannii , including an unusual, dual-functioning LpxM that catalyses transfer of acyl chains to two positions.

  20. 20.

    Eshghi, A., Henderson, J., Trent, M. S. & Picardeau, M. Leptospira interrogans lpxD homologue is required for thermal acclimatization and virulence. Infect. Immun. 83, 4314–4321 (2015).

  21. 21.

    Li, Y. et al. LPS remodeling is an evolved survival strategy for bacteria. Proc. Natl Acad. Sci. USA 109, 8716–8721 (2012).

  22. 22.

    Guo, L. et al. Lipid A acylation and bacterial resistance against vertebrate antimicrobial peptides. Cell 95, 189–198 (1998).

  23. 23.

    Reynolds, C. M. et al. An outer membrane enzyme encoded by Salmonella typhimurium lpxR that removes the 3´-acyloxyacyl moiety of lipid A. J. Biol. Chem. 281, 21974–21987 (2006).

  24. 24.

    Trent, M. S., Ribeiro, A. A., Lin, S., Cotter, R. J. & Raetz, C. R. An inner membrane enzyme in Salmonella and Escherichia coli that transfers 4-amino-4-deoxy-L-arabinose to lipid A: induction on polymyxin-resistant mutants and role of a novel lipid-linked donor. J. Biol. Chem. 276, 43122–43131 (2001).

  25. 25.

    Gibbons, H. S., Lin, S., Cotter, R. J. & Raetz, C. R. Oxygen requirement for the biosynthesis of the S-2-hydroxymyristate moiety in Salmonella typhimurium lipid A. Function of LpxO, A new Fe2+/α-ketoglutarate-dependent dioxygenase homologue. J. Biol. Chem. 275, 32940–32949 (2000).

  26. 26.

    Hankins, J. V., Madsen, J. A., Giles, D. K., Brodbelt, J. S. & Trent, M. S. Amino acid addition to Vibrio cholerae LPS establishes a link between surface remodeling in gram-positive and gram-negative bacteria. Proc. Natl Acad. Sci. USA 109, 8722–8727 (2012).

  27. 27.

    Needham, B. D. & Trent, M. S. Fortifying the barrier: the impact of lipid A remodelling on bacterial pathogenesis. Nat. Rev. Microbiol. 11, 467–481 (2013).

  28. 28.

    Kanistanon, D. et al. A Francisella mutant in lipid A carbohydrate modification elicits protective immunity. PLOS Pathog. 4, e24 (2008).

  29. 29.

    Herrera, C. M., Hankins, J. V. & Trent, M. S. Activation of PmrA inhibits LpxT-dependent phosphorylation of lipid A promoting resistance to antimicrobial peptides. Mol. Microbiol. 76, 1444–1460 (2010).

  30. 30.

    Nowicki, E. M., O’Brien, J. P., Brodbelt, J. S. & Trent, M. S. Characterization of Pseudomonas aeruginosa LpxT reveals dual positional lipid A kinase activity and co-ordinated control of outer membrane modification. Mol. Microbiol. 94, 728–741 (2014).

  31. 31.

    Lerouge, I. & Vanderleyden, J. O-Antigen structural variation: mechanisms and possible roles in animal/plant-microbe interactions. FEMS Microbiol. Rev. 26, 17–47 (2002).

  32. 32.

    Samuel, G. & Reeves, P. Biosynthesis of O-antigens: genes and pathways involved in nucleotide sugar precursor synthesis and O-antigen assembly. Carbohydr. Res. 338, 2503–2519 (2003).

  33. 33.

    Stead, C. et al. A novel 3-deoxy-D-manno-octulosonic acid (Kdo) hydrolase that removes the outer Kdo sugar of Helicobacter pylori lipopolysaccharide. J. Bacteriol. 187, 3374–3383 (2005).

  34. 34.

    Stead, C. M., Beasley, A., Cotter, R. J. & Trent, M. S. Deciphering the unusual acylation pattern of Helicobacter pylori lipid A. J. Bacteriol. 190, 7012–7021 (2008).

  35. 35.

    Tran, A. X. et al. Periplasmic cleavage and modification of the 1-phosphate group of Helicobacter pylori lipid A. J. Biol. Chem. 279, 55780–55791 (2004).

  36. 36.

    Tran, A. X., Stead, C. M. & Trent, M. S. Remodeling of Helicobacter pylori lipopolysaccharide. J. Endotoxin Res. 11, 161–166 (2005).

  37. 37.

    Chen, H. D. & Groisman, E. A. The biology of the PmrA/PmrB two-component system: the major regulator of lipopolysaccharide modifications. Annu. Rev. Microbiol. 67, 83–112 (2013).

  38. 38.

    Prost, L. R. & Miller, S. I. The Salmonellae PhoQ sensor: mechanisms of detection of phagosome signals. Cell. Microbiol. 10, 576–582 (2008).

  39. 39.

    Garcia Vescovi, E., Soncini, F. C. & Groisman, E. A. Mg2+ as an extracellular signal: environmental regulation of Salmonella virulence. Cell 84, 165–174 (1996).

  40. 40.

    Richards, S. M., Strandberg, K. L., Conroy, M. & Gunn, J. S. Cationic antimicrobial peptides serve as activation signals for the Salmonella Typhimurium PhoPQ and PmrAB regulons in vitro and in vivo. Front. Cell. Infect. Microbiol. 2, 102 (2012).

  41. 41.

    Yuan, J., Jin, F., Glatter, T. & Sourjik, V. Osmosensing by the bacterial PhoQ/PhoP two-component system. Proc. Natl Acad. Sci. USA 114, E10792–E10798 (2017).

  42. 42.

    Gooderham, W. J. et al. The sensor kinase PhoQ mediates virulence in Pseudomonas aeruginosa. Microbiology 155, 699–711 (2009).

  43. 43.

    Bader, M. W. et al. Recognition of antimicrobial peptides by a bacterial sensor kinase. Cell 122, 461–472 (2005).

  44. 44.

    Prost, L. R. et al. Activation of the bacterial sensor kinase PhoQ by acidic pH. Mol. Cell 26, 165–174 (2007).

  45. 45.

    Choi, J. & Groisman, E. A. Acidic pH sensing in the bacterial cytoplasm is required for Salmonella virulence. Mol. Microbiol. 101, 1024–1038 (2016).

  46. 46.

    Choi, J. & Groisman, E. A. Activation of master virulence regulator PhoP in acidic pH requires the Salmonella-specific protein UgtL. Sci. Signal. 10, eaan6284 (2017).

  47. 47.

    Guo, L. et al. Regulation of lipid A modifications by Salmonella typhimurium virulence genes phoP-phoQ. Science 276, 250–253 (1997).

  48. 48.

    Kox, L. F., Wosten, M. M. & Groisman, E. A. A small protein that mediates the activation of a two-component system by another two-component system. EMBO J. 19, 1861–1872 (2000).

  49. 49.

    Rubin, E. J., Herrera, C. M., Crofts, A. A. & Trent, M. S. PmrD is required for modifications to Escherichia coli endotoxin that promote antimicrobial resistance. Antimicrob. Agents Chemother. 59, 2051–2061 (2015).

  50. 50.

    Kato, A. & Groisman, E. A. Connecting two-component regulatory systems by a protein that protects a response regulator from dephosphorylation by its cognate sensor. Genes Dev. 18, 2302–2313 (2004).

  51. 51.

    Lippa, A. M. & Goulian, M. Feedback inhibition in the PhoQ/PhoP signaling system by a membrane peptide. PLOS Genet. 5, e1000788 (2009).

  52. 52.

    Wosten, M. M., Kox, L. F., Chamnongpol, S., Soncini, F. C. & Groisman, E. A. A signal transduction system that responds to extracellular iron. Cell 103, 113–125 (2000).

  53. 53.

    Perez, J. C. & Groisman, E. A. Acid pH activation of the PmrA/PmrB two-component regulatory system of Salmonella enterica. Mol. Microbiol. 63, 283–293 (2007).

  54. 54.

    Kato, A., Chen, H. D., Latifi, T. & Groisman, E. A. Reciprocal control between a bacterium’s regulatory system and the modification status of its lipopolysaccharide. Mol. Cell 47, 897–908 (2012).

  55. 55.

    Fernandez, P. A. et al. Fnr and ArcA regulate lipid A hydroxylation in Salmonella enteritidis by controlling lpxO expression in response to oxygen availability. Front. Microbiol. 9, 1220 (2018).

  56. 56.

    Nowicki, E. M., O’Brien, J. P., Brodbelt, J. S. & Trent, M. S. Extracellular zinc induces phosphoethanolamine addition to Pseudomonas aeruginosa lipid A via the ColRS two-component system. Mol. Microbiol. 97, 166–178 (2015).

  57. 57.

    Fernandez, L. et al. Adaptive resistance to the “last hope” antibiotics polymyxin B and colistin in Pseudomonas aeruginosa is mediated by the novel two-component regulatory system ParR-ParS. Antimicrob. Agents Chemother. 54, 3372–3382 (2010).

  58. 58.

    Fernandez, L. et al. The two-component system CprRS senses cationic peptides and triggers adaptive resistance in Pseudomonas aeruginosa independently of ParRS. Antimicrob. Agents Chemother. 56, 6212–6222 (2012).

  59. 59.

    Bilecen, K. et al. Polymyxin B resistance and biofilm formation in Vibrio cholerae are controlled by the response regulator CarR. Infect. Immun. 83, 1199–1209 (2015).

  60. 60.

    Herrera, C. M. et al. The Vibrio cholerae VprA-VprB. two-component system controls virulence through endotoxin modification. mBio 5, e02283–14 (2014).

  61. 61.

    Cheng, Y. H., Lin, T. L., Lin, Y. T. & Wang, J. T. Amino acid substitutions of CrrB responsible for resistance to colistin through CrrC in Klebsiella pneumoniae. Antimicrob. Agents Chemother. 60, 3709–3716 (2016).

  62. 62.

    Coornaert, A. et al. MicA sRNA links the PhoP regulon to cell envelope stress. Mol. Microbiol. 76, 467–479 (2010).

  63. 63.

    Moon, K. & Gottesman, S. A. PhoQ/P-regulated small RNA regulates sensitivity of Escherichia coli to antimicrobial peptides. Mol. Microbiol. 74, 1314–1330 (2009).

  64. 64.

    Kawasaki, K., Ernst, R. K. & Miller, S. I. Inhibition of Salmonella enterica serovar Typhimurium lipopolysaccharide deacylation by aminoarabinose membrane modification. J. Bacteriol. 187, 2448–2457 (2005).

  65. 65.

    Reines, M. et al. Deciphering the acylation pattern of Yersinia enterocolitica lipid A. PLoS Pathog. 8, e1002978 (2012).

  66. 66.

    Bishop, R. E. et al. Transfer of palmitate from phospholipids to lipid A in outer membranes of Gram-negative bacteria. EMBO J. 19, 5071–5080 (2000).

  67. 67.

    Jia, W. et al. Lipid trafficking controls endotoxin acylation in outer membranes of Escherichia coli. J. Biol. Chem. 279, 44966–44975 (2004).

  68. 68.

    Murata, T., Tseng, W., Guina, T., Miller, S. I. & Nikaido, H. PhoPQ-mediated regulation produces a more robust permeability barrier in the outer membrane of Salmonella enterica serovar typhimurium. J. Bacteriol. 189, 7213–7222 (2007). LPS modifications upregulated by PhoPQ and PmrAB alter the permeability of the outer membrane to be more stable in Mg 2+ -limiting environments but less stable in high-Mg 2+ -concentration environments.

  69. 69.

    Sassi, N., Paul, C., Martin, A., Bettaieb, A. & Jeannin, J. F. Lipid A-induced responses in vivo. Adv. Exp. Med. Biol. 667, 69–80 (2010).

  70. 70.

    Kong, Q. et al. Palmitoylation state impacts induction of innate and acquired immunity by the Salmonella enterica serovar Typhimurium msbB mutant. Infect. Immun. 79, 5027–5038 (2011).

  71. 71.

    Kong, Q. et al. Phosphate groups of lipid A are essential for Salmonella enterica serovar Typhimurium virulence and affect innate and adaptive immunity. Infect. Immun. 80, 3215–3224 (2012).

  72. 72.

    Casella, C. R. & Mitchell, T. C. Putting endotoxin to work for us: monophosphoryl lipid A as a safe and effective vaccine adjuvant. Cell. Mol. Life Sci. 65, 3231–3240 (2008).

  73. 73.

    Yamamoto, M. & Akira, S. Lipid A receptor TLR4-mediated signaling pathways. Adv. Exp. Med. Biol. 667, 59–68 (2010).

  74. 74.

    Cullen, T. W. et al. Helicobacter pylori versus the host: remodeling of the bacterial outer membrane is required for survival in the gastric mucosa. PLOS Pathog. 7, e1002454 (2011).

  75. 75.

    Mandell, L. et al. Intact gram-negative Helicobacter pylori, Helicobacter felis, and Helicobacter hepaticus bacteria activate innate immunity via toll-like receptor 2 but not toll-like receptor 4. Infect. Immun. 72, 6446–6454 (2004).

  76. 76.

    Llobet, E. et al. Deciphering tissue-induced Klebsiella pneumoniae lipid A structure. Proc. Natl Acad. Sci. USA 112, E6369–E6378 (2015).

  77. 77.

    Shi, J. et al. Inflammatory caspases are innate immune receptors for intracellular LPS. Nature 514, 187–192 (2014).

  78. 78.

    Hagar, J. A., Powell, D. A., Aachoui, Y., Ernst, R. K. & Miao, E. A. Cytoplasmic LPS activates caspase-11: implications in TLR4-independent endotoxic shock. Science 341, 1250–1253 (2013).

  79. 79.

    Kayagaki, N. et al. Noncanonical inflammasome activation by intracellular LPS independent of TLR4. Science 341, 1246–1249 (2013). Along with reference 78, this study discovered that murine caspase 11 interacts with cytoplasmic LPS and stimulates the inflammasome independently of TLR4.

  80. 80.

    Guo, H., Callaway, J. B. & Ting, J. P. Inflammasomes: mechanism of action, role in disease, and therapeutics. Nat. Med. 21, 677–687 (2015).

  81. 81.

    Lagrange, B. et al. Human caspase-4 detects tetra-acylated LPS and cytosolic Francisella and functions differently from murine caspase-11. Nat. Commun. 9, 242 (2018).

  82. 82.

    Peschel, A. & Sahl, H. G. The co-evolution of host cationic antimicrobial peptides and microbial resistance. Nat. Rev. Microbiol. 4, 529–536 (2006).

  83. 83.

    Faith, J. J. et al. The long-term stability of the human gut microbiota. Science 341, 1237439 (2013).

  84. 84.

    Cullen, T. W. et al. Gut microbiota. Antimicrobial peptide resistance mediates resilience of prominent gut commensals during inflammation. Science 347, 170–175 (2015). LPS modifications that mediate AMP resistance contribute to stable maintenance of the gut microbiota.

  85. 85.

    Schwarz, S. & Johnson, A. P. Transferable resistance to colistin: a new but old threat. J. Antimicrob. Chemother. 71, 2066–2070 (2016).

  86. 86.

    Schwechheimer, C. & Kuehn, M. J. Outer-membrane vesicles from Gram-negative bacteria: biogenesis and functions. Nat. Rev. Microbiol. 13, 605–619 (2015).

  87. 87.

    Haurat, M. F. et al. Selective sorting of cargo proteins into bacterial membrane vesicles. J. Biol. Chem. 286, 1269–1276 (2011).

  88. 88.

    Horstman, A. L. & Kuehn, M. J. Enterotoxigenic Escherichia coli secretes active heat-labile enterotoxin via outer membrane vesicles. J. Biol. Chem. 275, 12489–12496 (2000).

  89. 89.

    Horstman, A. L., Bauman, S. J. & Kuehn, M. J. Lipopolysaccharide 3-deoxy-D-manno-octulosonic acid (Kdo) core determines bacterial association of secreted toxins. J. Biol. Chem. 279, 8070–8075 (2004).

  90. 90.

    Chen, Y. Y. et al. The outer membrane protein LptO is essential for the O-deacylation of LPS and the co-ordinated secretion and attachment of A-LPS and CTD proteins in Porphyromonas gingivalis. Mol. Microbiol. 79, 1380–1401 (2011).

  91. 91.

    Rangarajan, M. et al. LptO (PG0027) is required for lipid A 1-phosphatase activity in Porphyromonas gingivalis W50. J. Bacteriol. 199, e00751–16 (2017).

  92. 92.

    Sato, K. et al. Identification of Porphyromonas gingivalis proteins secreted by the Por secretion system. FEMS Microbiol. Lett. 338, 68–76 (2013).

  93. 93.

    Gabarrini, G. et al. Conserved citrullinating exoenzymes in Porphyromonas species. J. Dent. Res. 97, 556–562 (2018).

  94. 94.

    Konig, M. F. et al. Defining the role of Porphyromonas gingivalis peptidylarginine deiminase (PPAD) in rheumatoid arthritis through the study of PPAD biology. Ann. Rheum. Dis. 74, 2054–2061 (2015).

  95. 95.

    Wegner, N. et al. Autoimmunity to specific citrullinated proteins gives the first clues to the etiology of rheumatoid arthritis. Immunol. Rev. 233, 34–54 (2010).

  96. 96.

    Gabarrini, G. et al. Dropping anchor: attachment of peptidylarginine deiminase via A-LPS to secreted outer membrane vesicles of Porphyromonas gingivalis. Sci. Rep. 8, 8949 (2018).

  97. 97.

    Gabarrini, G. et al. There’s no place like OM: vesicular sorting and secretion of the peptidylarginine deiminase of Porphyromonas gingivalis. Virulence 9, 456–464 (2018).

  98. 98.

    Mashburn-Warren, L. et al. Interaction of quorum signals with outer membrane lipids: insights into prokaryotic membrane vesicle formation. Mol. Microbiol. 69, 491–502 (2008).

  99. 99.

    Li, A., Schertzer, J. W. & Yong, X. Molecular conformation affects the interaction of the Pseudomonas quinolone signal with the bacterial outer membrane. J. Biol. Chem. 294, 1089–1094 (2018).

  100. 100.

    Elhenawy, W. et al. LPS remodeling triggers formation of outer membrane vesicles in Salmonella. mBio 7, e00940–16 (2016). PagL-mediated deacylation of LPS in S . Typhimurium stimulates production of OMVs.

  101. 101.

    Bonnington, K. E. & Kuehn, M. J. Outer membrane vesicle production facilitates LPS remodeling and outer membrane maintenance in Salmonella during environmental transitions. mBio 7, e01532–16 (2016). During environmental transitions that alter LPS modification, certain LPS species are selectively secreted and others are under-represented in OMVs.

  102. 102.

    Cipolla, L. et al. New targets for antibacterial design: Kdo biosynthesis and LPS machinery transport to the cell surface. Curr. Med. Chem. 18, 830–852 (2011).

  103. 103.

    Zhou, P. & Zhao, J. Structure, inhibition, and regulation of essential lipid A enzymes. Biochim. Biophys. Acta Mol. Cell Biol. Lipids 1862, 1424–1438 (2017).

  104. 104.

    Erwin, A. L. Antibacterial drug discovery targeting the lipopolysaccharide biosynthetic enzyme LpxC. Cold Spring Harb. Perspect. Med. 6, a025304 (2016).

  105. 105.

    Richie, D. L. et al. Toxic accumulation of LPS pathway intermediates underlies the requirement of LpxH for growth of Acinetobacter baumannii ATCC 19606. PLOS ONE 11, e0160918 (2016).

  106. 106.

    Wei, J. R. et al. LpxK is essential for growth of Acinetobacter baumannii ATCC 19606: relationship to toxic accumulation of lipid A pathway intermediates. mSphere 2, e00199–17 (2017).

  107. 107.

    Piizzi, G. et al. Design, synthesis, and properties of a potent inhibitor of Pseudomonas aeruginosa deacetylase LpxC. J. Med. Chem. 60, 5002–5014 (2017).

  108. 108.

    Pratap, S. et al. Acyl chain preference and inhibitor identification of Moraxella catarrhalis LpxA: Insight through crystal structure and computational studies. Int. J. Biol. Macromol. 96, 759–765 (2017).

  109. 109.

    Nayar, A. S. et al. Novel antibacterial targets and compounds revealed by a high-throughput cell wall reporter assay. J. Bacteriol. 197, 1726–1734 (2015).

  110. 110.

    Richie, D. L. et al. A pathway-directed positive growth restoration assay to facilitate the discovery of lipid A and fatty acid biosynthesis inhibitors in Acinetobacter baumannii. PLOS ONE 13, e0193851 (2018).

  111. 111.

    Ho, H. et al. Structural basis for dual-mode inhibition of the ABC transporter MsbA. Nature 557, 196–201 (2018).

  112. 112.

    Zhang, G. et al. Cell-based screen for discovering lipopolysaccharide biogenesis inhibitors. Proc. Natl Acad. Sci. USA 115, 6834–6839 (2018).

  113. 113.

    May, J. M. et al. The antibiotic novobiocin binds and activates the ATPase that powers lipopolysaccharide transport. J. Am. Chem. Soc. 139, 17221–17224 (2017).

  114. 114.

    Mandler, M. D. et al. Novobiocin enhances polymyxin activity by stimulating lipopolysaccharide transport. J. Am. Chem. Soc. 140, 6749–6753 (2018).

  115. 115.

    Srinivas, N. et al. Peptidomimetic antibiotics target outer-membrane biogenesis in Pseudomonas aeruginosa. Science 327, 1010–1013 (2010).

  116. 116.

    Vetterli, S. U., Moehle, K. & Robinson, J. A. Synthesis and antimicrobial activity against Pseudomonas aeruginosa of macrocyclic beta-hairpin peptidomimetic antibiotics containing N-methylated amino acids. Bioorg. Med. Chem. 24, 6332–6339 (2016).

  117. 117.

    Werneburg, M. et al. Inhibition of lipopolysaccharide transport to the outer membrane in Pseudomonas aeruginosa by peptidomimetic antibiotics. Chembiochem 13, 1767–1775 (2012).

  118. 118.

    Vetterli, S. U. et al. Thanatin targets the intermembrane protein complex required for lipopolysaccharide transport in Escherichia coli. Sci. Adv. 4, eaau2634 (2018).

  119. 119.

    Zhang, X. et al. Identification of an anti-Gram-negative bacteria agent disrupting the interaction between LPS transporters LptA and LptC. Int. J. Antimicrob. Agents 53, 442–448 (2018).

  120. 120.

    Harris, T. L. et al. Small molecule downregulation of PmrAB reverses lipid A modification and breaks colistin resistance. ACS Chem. Biol. 9, 122–127 (2014).

  121. 121.

    Kline, T. et al. Synthesis of and evaluation of lipid A modification by 4-substituted 4-deoxy arabinose analogs as potential inhibitors of bacterial polymyxin resistance. Bioorg. Med. Chem. Lett. 18, 1507–1510 (2008).

  122. 122.

    Anandan, A. et al. Structure of a lipid A phosphoethanolamine transferase suggests how conformational changes govern substrate binding. Proc. Natl Acad. Sci. USA 114, 2218–2223 (2017).

  123. 123.

    Touze, T., Tran, A. X., Hankins, J. V., Mengin-Lecreulx, D. & Trent, M. S. Periplasmic phosphorylation of lipid A is linked to the synthesis of undecaprenyl phosphate. Mol. Microbiol. 67, 264–277 (2008).

  124. 124.

    Cullen, T. W. et al. EptC of Campylobacter jejuni mediates phenotypes involved in host interactions and virulence. Infect. Immun. 81, 430–440 (2013).

  125. 125.

    Cullen, T. W. & Trent, M. S. A link between the assembly of flagella and lipooligosaccharide of the Gram-negative bacterium Campylobacter jejuni. Proc. Natl Acad. Sci. USA 107, 5160–5165 (2010).

  126. 126.

    Bach, J. F. & Chatenoud, L. The hygiene hypothesis: an explanation for the increased frequency of insulin-dependent diabetes. Cold Spring Harb. Perspect. Med. 2, a007799 (2012).

  127. 127.

    Vatanen, T. et al. Variation in microbiome LPS immunogenicity contributes to autoimmunity in humans. Cell 165, 1551 (2016).

  128. 128.

    Raetz, C. R., Reynolds, C. M., Trent, M. S. & Bishop, R. E. Lipid A modification systems in gram-negative bacteria. Annu. Rev. Biochem. 76, 295–329 (2007).

  129. 129.

    Moffatt, J. H. et al. Colistin resistance in Acinetobacter baumannii is mediated by complete loss of lipopolysaccharide production. Antimicrob. Agents Chemother. 54, 4971–4977 (2010).

  130. 130.

    Peng, D., Hong, W., Choudhury, B. P., Carlson, R. W. & Gu, X. X. Moraxella catarrhalis bacterium without endotoxin, a potential vaccine candidate. Infect. Immun. 73, 7569–7577 (2005).

  131. 131.

    Steeghs, L. et al. Meningitis bacterium is viable without endotoxin. Nature 392, 449–450 (1998).

  132. 132.

    Beceiro, A. et al. Biological cost of different mechanisms of colistin resistance and their impact on virulence in Acinetobacter baumannii. Antimicrob. Agents Chemother. 58, 518–526 (2014).

  133. 133.

    Boll, J. M. et al. A penicillin-binding protein inhibits selection of colistin-resistant, lipooligosaccharide-deficient Acinetobacter baumannii. Proc. Natl Acad. Sci. USA 113, E6228–E6237 (2016).

  134. 134.

    Henry, R. et al. Colistin-resistant, lipopolysaccharide-deficient Acinetobacter baumannii responds to lipopolysaccharide loss through increased expression of genes involved in the synthesis and transport of lipoproteins, phospholipids, and poly-beta-1,6-N-acetylglucosamine. Antimicrob. Agents Chemother. 56, 59–69 (2012).

  135. 135.

    Powers, M. J. & Trent, M. S. Phospholipid retention in the absence of asymmetry strengthens the outer membrane permeability barrier to last-resort antibiotics. Proc. Natl Acad. Sci. USA 115, E8518–E8527 (2018).

  136. 136.

    Qureshi, N., Takayama, K. & Ribi, E. Purification and structural determination of nontoxic lipid A obtained from the lipopolysaccharide of Salmonella typhimurium. J. Biol. Chem. 257, 11808–11815 (1982).

  137. 137.

    Needham, B. D. et al. Modulating the innate immune response by combinatorial engineering of endotoxin. Proc. Natl Acad. Sci. USA 110, 1464–1469 (2013).

  138. 138.

    Gregg, K. A. et al. Rationally designed TLR4 ligands for vaccine adjuvant discovery. mBio 8, e00492–17 (2017).

  139. 139.

    Zariri, A., Pupo, E., van Riet, E., van Putten, J. P. & van der Ley, P. Modulating endotoxin activity by combinatorial bioengineering of meningococcal lipopolysaccharide. Sci. Rep. 6, 36575 (2016).

  140. 140.

    Sanders, H. & Feavers, I. M. Adjuvant properties of meningococcal outer membrane vesicles and the use of adjuvants in Neisseria meningitidis protein vaccines. Expert Rev. Vaccines 10, 323–334 (2011).

  141. 141.

    Price, N. L. et al. Glycoengineered outer membrane vesicles: a novel platform for bacterial vaccines. Sci. Rep. 6, 24931 (2016). This study engineered non-pathogenic E. coli to produce LPS modified with glycans from pathogenic bacteria, such as capsule from Streptococcus pneumoniae and heptasaccharide N -glycan from C. jejuni, that can be isolated in OMVs and used as vaccines.

  142. 142.

    Chen, L. et al. Outer membrane vesicles displaying engineered glycotopes elicit protective antibodies. Proc. Natl Acad. Sci. USA 113, E3609–E3618 (2016). This study engineered non-pathogenic E. coli to produce LPS modified with glycans from pathogenic bacteria, such as O antigen from F. tularensis subsp. tularensis, that can be isolated in OMVs and used as vaccines.

  143. 143.

    Valentine, J. L. et al. Immunization with outer membrane vesicles displaying designer glycotopes yields class-switched, glycan-specific antibodies. Cell Chem. Biol. 23, 655–665 (2016).

  144. 144.

    Zhou, Z., White, K. A., Polissi, A., Georgopoulos, C. & Raetz, C. R. Function of Escherichia coli MsbA, an essential ABC family transporter, in lipid A and phospholipid biosynthesis. J. Biol. Chem. 273, 12466–12475 (1998).

  145. 145.

    Mamat, U. et al. Single amino acid substitutions in either YhjD or MsbA confer viability to 3-deoxy-d-manno-oct-2-ulosonic acid-depleted Escherichia coli. Mol. Microbiol. 67, 633–648 (2008).

  146. 146.

    Mi, W. et al. Structural basis of MsbA-mediated lipopolysaccharide transport. Nature 549, 233–237 (2017). This structural snapshot of MsbA 2 in complex with LPS suggests a ‘trap and flip’ model for LPS flipping across the inner membrane.

  147. 147.

    Ortega, X. P. et al. A putative gene cluster for aminoarabinose biosynthesis is essential for Burkholderia cenocepacia viability. J. Bacteriol. 189, 3639–3644 (2007).

  148. 148.

    Hamad, M. A., Di Lorenzo, F., Molinaro, A. & Valvano, M. A. Aminoarabinose is essential for lipopolysaccharide export and intrinsic antimicrobial peptide resistance in Burkholderia cenocepacia. Mol. Microbiol. 85, 962–974 (2012).

  149. 149.

    Bertani, B. R., Taylor, R. J., Nagy, E., Kahne, D. & Ruiz, N. A cluster of residues in the lipopolysaccharide exporter that selects substrate variants for transport to the outer membrane. Mol. Microbiol. 109, 541–554 (2018). In E. coli , extraction of LPS from the inner membrane by the LPS transporter requires interactions with the 1 and 4′ positions of lipid A.

  150. 150.

    Li, Y., Orlando, B. J. & Liao, M. Structural basis of lipopolysaccharide extraction by the LptB2FGC complex. Nature 567, 486–490 (2019).

  151. 151.

    Owens, T. W. et al. Structural basis of unidirectional export of lipopolysaccharide to the cell surface. Nature 567, 550–553 (2019).

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The authors gratefully acknowledge funding from the National Institutes of Health (RO1s AI129940, AI138576, AI076322 to M.S.T.)

Reviewer information

Nature Reviews Microbiology thanks Mario Feldman, Marcin Grabowicz and Alessandra Polissi for their contribution to the peer review of this work.

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Both authors researched data for the article, discussed the content, wrote the article and reviewed and edited the manuscript before submission.

Competing interests

The authors declare no conflicts of interest.

Correspondence to M. Stephen Trent.

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  1. Supplementary Information



(LOS). A form of lipopolysaccharide with an extended core oligosaccharide, but lacking O antigen.

Outer membrane vesicles

(OMVs). Small, spherical outer membrane blebs that are released from Gram-negative bacterial cells and contain membrane and periplasmic components.

Small RNAs

(sRNAs). Typically short, non-coding RNA molecules that interact with mRNAs to regulate gene expression or interact with proteins to regulate activity.


An intracellular, multiprotein complex in mammalian cells that recognizes microbial molecules and activates inflammatory responses, including pyroptosis and proinflammatory cytokines.

Toll-like receptor 4–myeloid differentiation factor 2

(TLR4–MD2). A pattern-recognition receptor of the innate immune system that recognizes lipopolysaccharide and lipooligosaccharide, initiating a robust signal cascade and inflammatory responses in mammals.


An inflammatory, programmed cell death that typically is associated with infection of intracellular pathogens.


A thick layer of polysaccharides that surrounds a bacterial cell, also referred to as capsular polysaccharide.

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Fig. 1: Lipopolysaccharide biogenesis, structure and modifications.
Fig. 2: Regulation of lipopolysaccharide modifications.
Fig. 3: Consequences of lipopolysaccharide modifications.
Fig. 4: Summary of therapeutic strategies to target lipopolysaccharide biogenesis.