Umeå University's logo

umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Acinetobacter baumannii Can Survive with an Outer Membrane Lacking Lipooligosaccharide Due to Structural Support from Elongasome Peptidoglycan Synthesis
Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, GA, Athens, United States.
Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, GA, Athens, United States.
Show others and affiliations
2021 (English)In: mBio, ISSN 2161-2129, E-ISSN 2150-7511, Vol. 12, no 6, article id e03099-21Article in journal (Refereed) Published
Abstract [en]

Gram-negative bacteria resist external stresses due to cell envelope rigidity, which is provided by two membranes and a peptidoglycan layer. The outer membrane (OM) surface contains lipopolysaccharide (LPS; contains O-antigen) or lipooligosaccharide (LOS). LPS/LOS are essential in most Gram-negative bacteria and may contribute to cellular rigidity. Acinetobacter baumannii is a useful tool for testing these hypotheses as it can survive without LOS. Previously, our group found that strains with naturally high levels of penicillin binding protein 1A (PBP1A) could not become LOS deficient unless the gene encoding it was deleted, highlighting the relevance of peptidoglycan biosynthesis and suggesting that high PBP1A levels were toxic during LOS deficiency. Transposon sequencing and follow-up analysis found that axial peptidoglycan synthesis by the elongasome and a peptidoglycan recycling enzyme, ElsL, were vital in LOS-deficient cells. The toxicity of high PBP1A levels during LOS deficiency was clarified to be due to a negative impact on elongasome function. Our data suggest that during LOS deficiency, the strength of the peptidoglycan specifically imparted by elongasome synthesis becomes essential, supporting that the OM and peptidoglycan contribute to cell rigidity. IMPORTANCE Gram-negative bacteria have a multilayered cell envelope with a layer of cross-linked polymers (peptidoglycan) sandwiched between two membranes. Peptidoglycan was long thought to exclusively provide rigidity to the cell providing mechanical strength. Recently, the most outer membrane of the cell was also proposed to contribute to rigidity due to properties of a unique molecule called lipopolysaccharide (LPS). LPS is located on the cell surface in the outer membrane and is typically required for growth. By using Acinetobacter baumannii, a Gram-negative bacterium that can grow without LPS, we found that key features of the peptidoglycan structure also become essential. This finding supports that both the outer membrane and peptidoglycan contribute to cell rigidity.

Place, publisher, year, edition, pages
American Society for Microbiology , 2021. Vol. 12, no 6, article id e03099-21
Keywords [en]
Carboxypeptidase, Cell envelope, ElsL, Lipopolysaccharide, Outer membrane, PBP1A, Peptidoglycan
National Category
Microbiology in the medical area Microbiology
Identifiers
URN: urn:nbn:se:umu:diva-191116DOI: 10.1128/mBio.03099-21ISI: 000736925100002PubMedID: 34844428Scopus ID: 2-s2.0-85122087371OAI: oai:DiVA.org:umu-191116DiVA, id: diva2:1625992
Available from: 2022-01-10 Created: 2022-01-10 Last updated: 2024-11-06Bibliographically approved
In thesis
1. Studies on cell wall biosynthesis and remodeling in Acinetobacter baumannii
Open this publication in new window or tab >>Studies on cell wall biosynthesis and remodeling in Acinetobacter baumannii
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Studier om cellväggens biosyntes och ombyggnad hos Acinetobacter baumannii
Abstract [en]

The bacterial cell envelope is a complex and dynamic structure with essential functions in fitness and adaptation. In Gram-negative bacteria, the envelope is composed of an inner (IM) and an outer membrane (OM) that create a space in between called periplasm, where the peptidoglycan (PG) cell wall is located. This PG forms a net-like structure that surrounds the bacteria, determining its shape, counteracting osmotic pressure, and serving as a scaffold for proteins. PG synthesis starts in the cytoplasm, where the membrane-associated PG precursor lipid-II is made through a series of reactions. Lipid-II is then flipped into the periplasm, where it is polymerized to build the mature the sacculus. In rod-shaped bacteria such as Escherichia coli, two multiprotein complexes are responsible for PG synthesis: the divisome (septal synthesis) and the elongasome (axial synthesis). Since the discovery of penicillin, PG synthesis has been the focus of research due to its importance as therapeutic target. In this thesis, we explore various mechanisms that contribute to envelope homeostasis in the pathogen Acinetobacter baumannii. In the first chapter, we examine the remarkable ability of A. baumannii to survive without the elongasome. We phenotypically characterized deletion mutants of the genes encoding the individual components of the elongasome, followed by long-term evolution experiments to identify genetic cues that could explain the non-essentiality of the elongasome in this bacterium. The second chapter of the thesis focuses on the study of ElsL, an uncharacterized protein that allowed A. baumannii to keep its rod shape and withstand antibiotics that attack the septum of the cell wall. Although ElsL possesses a YkuD-like domain, which is usually found in periplasmic L,D-transpeptidases, we showed that ElsL is actually a cytoplasmic L,D-carboxypeptidase involved in PG recycling. Absence of ElsL produces a toxic build-up of murein tetrapeptide precursors that negatively affects cell wall integrity. Additionally, inactivation of ElsL perturbs other pathways such as outer membrane lipid homeostasis or L,D-crosslink formation. In the third chapter we focus on the crosstalk between the OM and the PG in A. baumannii. This bacterium is an outstanding model to study OM contribution in envelope stability due to its ability to lose its lipooligosacharide (LOS) layer. Using transposon sequencing we found that the elongasome and the PG recycling enzyme ElsL are essential in LOS-deficient A. baumannii strains. We further demonstrated that high PBP1A levels impacted negatively on the elongasome function, thus preventing these strains to lose their LOS. In the final chapter of the thesis, we studied how A. baumannii employs its type VI secretion system to kill Gram-positive and Gram-negative bacteria. This is dependent on Tse4, a bifunctional enzyme possessing lytic transglycosylase and endopeptidase activities. Additionally, we showed that A. baumannii also secretes D-lysine, which gets incorporated into its PG and increased the pH of the environment to enhance Tse4 activity.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2024. p. 34
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 2333
Keywords
Peptidoglycan, lipopolysaccharide, bacterial cell wall, antibiotics, Acinetobacter baumannii, elongasome
National Category
Microbiology in the medical area Microbiology
Identifiers
urn:nbn:se:umu:diva-231493 (URN)978-91-8070-548-6 (ISBN)978-91-8070-549-3 (ISBN)
Public defence
2024-12-13, Major Groove, Building 6L, NUS, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2024-11-22 Created: 2024-11-06 Last updated: 2024-11-07Bibliographically approved

Open Access in DiVA

fulltext(3593 kB)608 downloads
File information
File name FULLTEXT01.pdfFile size 3593 kBChecksum SHA-512
a5366fe7e2b9b2648ab5e3f813d0780fae4a2f4f0a720c0a516f7b66b28f7307dab84e17090e5e15e1ea76204ab181ee494d200195af1509283bde81ace2fc21
Type fulltextMimetype application/pdf

Other links

Publisher's full textPubMedScopus

Authority records

Nieckarz, MartaPinedo, VictorCava, Felipe

Search in DiVA

By author/editor
Nieckarz, MartaPinedo, VictorCava, Felipe
By organisation
Molecular Infection Medicine Sweden (MIMS)Umeå Centre for Microbial Research (UCMR)Department of Molecular Biology (Faculty of Medicine)
In the same journal
mBio
Microbiology in the medical areaMicrobiology

Search outside of DiVA

GoogleGoogle Scholar
Total: 609 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

doi
pubmed
urn-nbn

Altmetric score

doi
pubmed
urn-nbn
Total: 292 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf