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Studies on cell wall recycling and modification in Gram-negative bacteria
Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).ORCID iD: 0000-0002-6848-5134
2024 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Studier om cellväggsåtervinning och modifiering i gramnegativa bakterier (Swedish)
Abstract [en]

The bacterial cell wall is made from peptidoglycan (PG), a heteropolymer which forms a bag-like exoskeleton that envelopes the cell. PG is constantly remodelled during growth and division, and in response to environmental stimuli. Decades of study of this process have focused largely on a select few model organisms, leaving its diversity poorly understood. In this thesis, I present studies on different aspects of PG recycling and modification in several Gram-negative models, with a particular focus on the plant pathogen Agrobacterium tumefaciens, a model of the Hyphomicrobiales group of the Alphaproteobacteria which includes several species of medical and environmental interest. It is shown that A. tumefaciens encodes a novel PG transporter, which is vital for cell wall integrity and resistance to β- lactam antibiotics, and widely conserved in the Hyphomicrobiales and Rhodobacterales orders. Growth defects caused by the loss of the transporter are suppressed by mutations in a novel glycopolymer, which is hypothesized to play a role in sequestering metal ions and thereby lowering periplasmic oxidative stress. Next, in collaboration, it is shown that PG recycling in the best studied model, Escherichia coli, is more complicated than previously thought. Rather than depending mostly on the MFS-family transporter AmpG, E. coli uses an ABC transporter, MppA-OppBCDF or AmpG depending on the growth phase and conditions. Finally, two studies on modification of PG by deacetylation are presented. First, A. tumefaciens is shown to encode a novel anhydroMurNAc deacetylase, which specifically deacetylates the PG chain termini. Then, it is shown that the causative agent of Legionnaires’ disease, Legionella pneumophila, depends on deacetylation of its PG during infection for defence against host lysozyme and correct polar placement of its type IV secretion system. 

Place, publisher, year, edition, pages
Umeå: Umeå University, 2024. , p. 53
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 2300
Keywords [en]
Peptidoglycan recycling, bacterial cell wall, antibiotics, Agrobacterium tumefaciens, Escherichia coli, Legionella pneumophila
National Category
Microbiology
Research subject
Microbiology; Biochemistry
Identifiers
URN: urn:nbn:se:umu:diva-222530ISBN: 978-91-8070-295-9 (print)ISBN: 978-91-8070-296-6 (print)OAI: oai:DiVA.org:umu-222530DiVA, id: diva2:1845849
Public defence
2024-04-19, Major Groove, Building 6L, Norrlands Universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Note

Number in series missing in publication. 

Available from: 2024-03-28 Created: 2024-03-20 Last updated: 2024-03-21Bibliographically approved
List of papers
1. Peptidoglycan recycling mediated by an ABC transporter in the plant pathogen Agrobacterium tumefaciens
Open this publication in new window or tab >>Peptidoglycan recycling mediated by an ABC transporter in the plant pathogen Agrobacterium tumefaciens
2022 (English)In: Nature Communications, E-ISSN 2041-1723, Vol. 13, no 1, article id 7927Article in journal (Refereed) Published
Abstract [en]

During growth and division, the bacterial cell wall peptidoglycan (PG) is remodelled, resulting in the liberation of PG muropeptides which are typically reinternalized and recycled. Bacteria belonging to the Rhizobiales and Rhodobacterales orders of the Alphaproteobacteria lack the muropeptide transporter AmpG, despite having other key PG recycling enzymes. Here, we show that an alternative transporter, YejBEF-YepA, takes over this role in the Rhizobiales phytopathogen Agrobacterium tumefaciens. Muropeptide import by YejBEF-YepA governs expression of the β-lactamase AmpC in A. tumefaciens, contributing to β-lactam resistance. However, we show that the absence of YejBEF-YepA causes severe cell wall defects that go far beyond lowered AmpC activity. Thus, contrary to previously established Gram-negative models, PG recycling is vital for cell wall integrity in A. tumefaciens. YepA is widespread in the Rhizobiales and Rhodobacterales, suggesting that YejBEF-YepA-mediated PG recycling could represent an important but overlooked aspect of cell wall biology in these bacteria.

Place, publisher, year, edition, pages
Nature Publishing Group, 2022
National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-202244 (URN)10.1038/s41467-022-35607-5 (DOI)000971044000010 ()36566216 (PubMedID)2-s2.0-85144637346 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationThe Kempe Foundations
Available from: 2023-01-09 Created: 2023-01-09 Last updated: 2024-03-20Bibliographically approved
2. A metal ion-sequestering polymer protects the Agrobacterium tumefaciens periplasm from oxidative damage
Open this publication in new window or tab >>A metal ion-sequestering polymer protects the Agrobacterium tumefaciens periplasm from oxidative damage
(English)Manuscript (preprint) (Other academic)
National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-222529 (URN)
Available from: 2024-03-20 Created: 2024-03-20 Last updated: 2024-04-02
3. Escherichia coli utilizes multiple peptidoglycan recycling permeases with distinct strategies of recycling
Open this publication in new window or tab >>Escherichia coli utilizes multiple peptidoglycan recycling permeases with distinct strategies of recycling
Show others...
2023 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 120, no 44, article id e2308940120Article in journal (Refereed) Published
Abstract [en]

Bacteria produce a structural layer of peptidoglycan (PG) that enforces cell shape, resists turgor pressure, and protects the cell. As bacteria grow and divide, the existing layer of PG is remodeled and PG fragments are released. Enterics such as Escherichia coli go to great lengths to internalize and reutilize PG fragments. E. coli is estimated to break down one-third of its cell wall, yet only loses ~0 to 5% of meso-diaminopimelic acid, a PG-specific amino acid, per generation. Two transporters were identified early on to possibly be the primary permease that facilitates PG fragment recycling, i) AmpG and ii) the Opp ATP binding cassette transporter in conjunction with a PG-specific periplasmic binding protein, MppA. The contribution of each transporter to PG recycling has been debated. Here, we have found that AmpG and MppA/Opp are differentially regulated by carbon source and growth phase. In addition, MppA/Opp is uniquely capable of high-affinity scavenging of muropeptides from growth media, demonstrating that AmpG and MppA/Opp allow for different strategies of recycling PG fragments. Altogether, this work clarifies environmental contexts under which E. coli utilizes distinct permeases for PG recycling and explores how scavenging by MppA/Opp could be beneficial in mixed communities.

Place, publisher, year, edition, pages
Proceedings of the National Academy of Sciences (PNAS), 2023
Keywords
AmpG, cell wall, muropeptides, peptidoglycan, peptidoglycan recycling
National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-216380 (URN)10.1073/pnas.2308940120 (DOI)001124085100001 ()37871219 (PubMedID)2-s2.0-85175497598 (Scopus ID)
Funder
Swedish Research Council, 2018-05882Swedish Research Council, 2018-02823Knut and Alice Wallenberg Foundation, KAW2012.0184The Kempe FoundationsNIH (National Institutes of Health), AI176776NIH (National Institutes of Health), AI138576NIH (National Institutes of Health), AI150098NIH (National Institutes of Health), F32 GM137554
Available from: 2023-11-10 Created: 2023-11-10 Last updated: 2024-03-20Bibliographically approved
4. A peptidoglycan N-deacetylase specific for anhydroMurNAc chain termini in Agrobacterium tumefaciens
Open this publication in new window or tab >>A peptidoglycan N-deacetylase specific for anhydroMurNAc chain termini in Agrobacterium tumefaciens
Show others...
2024 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 300, no 2, article id 105611Article in journal (Refereed) Published
Abstract [en]

During growth, bacteria remodel and recycle their peptidoglycan (PG). A key family of PG-degrading enzymes is the lytic transglycosylases, which produce anhydromuropeptides, a modification that caps the PG chains and contributes to bacterial virulence. Previously, it was reported that the polar-growing Gram-negative plant pathogen Agrobacterium tumefaciens lacks anhydromuropeptides. Here, we report the identification of an enzyme, MdaA (MurNAc deacetylase A), which specifically removes the acetyl group from anhydromuropeptide chain termini in A. tumefaciens, resolving this apparent anomaly. A. tumefaciens lacking MdaA accumulates canonical anhydromuropeptides, whereas MdaA was able to deacetylate anhydro-N-acetyl muramic acid in purified sacculi that lack this modification. As for other PG deacetylases, MdaA belongs to the CE4 family of carbohydrate esterases but harbors an unusual Cys residue in its active site. MdaA is conserved in other polar-growing bacteria, suggesting a possible link between PG chain terminus deacetylation and polar growth.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Agrobacterium tumefaciens, anhydromuropeptide, deacetylase, lytic transglycosylase, peptidoglycan
National Category
Microbiology Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-220439 (URN)10.1016/j.jbc.2023.105611 (DOI)38159848 (PubMedID)2-s2.0-85183154845 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationThe Kempe Foundations
Available from: 2024-02-07 Created: 2024-02-07 Last updated: 2024-03-20Bibliographically approved
5. Peptidoglycan deacetylation controls type IV secretion and the intracellular survival of the bacterial pathogen Legionella pneumophila
Open this publication in new window or tab >>Peptidoglycan deacetylation controls type IV secretion and the intracellular survival of the bacterial pathogen Legionella pneumophila
Show others...
2023 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 120, no 23, article id  e2119658120Article in journal (Refereed) Published
Abstract [en]

Peptidoglycan is a critical component of the bacteria cell envelope. Remodeling of the peptidoglycan is required for numerous essential cellular processes and has been linked to bacterial pathogenesis. Peptidoglycan deacetylases that remove the acetyl group of the N-acetylglucosamine (NAG) subunit protect bacterial pathogens from immune recognition and digestive enzymes secreted at the site of infection. However, the full extent of this modification on bacterial physiology and pathogenesis is not known. Here, we identify a polysaccharide deacetylase of the intracellular bacterial pathogen Legionella pneumophila and define a two-tiered role for this enzyme in Legionella pathogenesis. First, NAG deacetylation is important for the proper localization and function of the Type IVb secretion system, linking peptidoglycan editing to the modulation of host cellular processes through the action of secreted virulence factors. As a consequence, the Legionella vacuole mis-traffics along the endocytic pathway to the lysosome, preventing the formation of a replication permissive compartment. Second, within the lysosome, the inability to deacetylate the peptidoglycan renders the bacteria more sensitive to lysozyme-mediated degradation, resulting in increased bacterial death. Thus, the ability to deacetylate NAG is important for bacteria to persist within host cells and in turn, Legionella virulence. Collectively, these results expand the function of peptidoglycan deacetylases in bacteria, linking peptidoglycan editing, Type IV secretion, and the intracellular fate of a bacterial pathogen.

Place, publisher, year, edition, pages
Proceedings of the National Academy of Sciences (PNAS), 2023
Keywords
DotK, Legionella, peptidoglycan, polysaccharide deacetylase, type IV secretion system
National Category
Microbiology in the medical area Microbiology
Identifiers
urn:nbn:se:umu:diva-209548 (URN)10.1073/pnas.2119658120 (DOI)37252954 (PubMedID)2-s2.0-85160607728 (Scopus ID)
Funder
NIH (National Institutes of Health), AI119580-01
Available from: 2023-06-13 Created: 2023-06-13 Last updated: 2024-03-20Bibliographically approved

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Gilmore, Michael C.

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