scholarly journals Mechanisms of Resistance to the Contact-Dependent Bacteriocin CdzC/D inCaulobacter crescentus

2019 ◽  
Vol 201 (8) ◽  
Author(s):  
Leonor García-Bayona ◽  
Kevin Gozzi ◽  
Michael T. Laub
Keyword(s):  
Outer Membrane ◽  
Caulobacter Crescentus ◽  
Cell Envelope ◽  
Target Cells ◽  
Dependent Manner ◽  
Content Type ◽  
Repeat Protein ◽  
Outer Membranes ◽  
Oligotrophic Bacterium ◽  
Small Hydrophobic

ABSTRACTThe Cdz bacteriocin system allows the aquatic oligotrophic bacteriumCaulobacter crescentusto kill closely related species in a contact-dependent manner. The toxin, which aggregates on the surfaces of producer cells, is composed of two small hydrophobic proteins, CdzC and CdzD, each bearing an extended glycine-zipper motif, that together induce inner membrane depolarization and kill target cells. To further characterize the mechanism of Cdz delivery and toxicity, we screened for mutations that render a target strain resistant to Cdz-mediated killing. These mutations mapped to four loci, including a TonB-dependent receptor, a three-gene operon (namedzerRABforzipperenveloperesistance), andperA(forpentapeptideenveloperesistance). Mutations in thezerRABlocus led to its overproduction and to potential changes in cell envelope composition, which may diminish the susceptibility of cells to Cdz toxins. TheperAgene is also required to maintain a normal cell envelope, but our screen identified mutations that confer resistance to Cdz toxins without substantially affecting the cell envelope functions of PerA. We demonstrate that PerA, which encodes a pentapeptide repeat protein predicted to form a quadrilateral β-helix, localizes primarily to the outer membrane of cells, where it may serve as a receptor for the Cdz toxins. Collectively, these results provide new insights into the function and mechanisms of an atypical, contact-dependent bacteriocin system.IMPORTANCEBacteriocins are commonly used by bacteria to kill neighboring cells that compete for resources. Although most bacteriocins are secreted, the aquatic, oligotrophic bacteriumCaulobacter crescentusproduces a two-peptide bacteriocin, CdzC/D, that remains attached to the outer membranes of cells, enabling contact-dependent killing of cells lacking the immunity protein CdzI. The receptor for CdzC/D has not previously been reported. Here, we describe a genetic screen for mutations that confer resistance to CdzC/D. One locus identified,perA, encodes a pentapeptide repeat protein that resides in the outer membrane of target cells, where it may act as the direct receptor for CdzC/D. Collectively, our results provide new insight into bacteriocin function and diversity.

scholarly journals A Multiprotein Complex Anchors Adhesive Holdfast at the Outer Membrane ofCaulobacter crescentus

2019 ◽  
Vol 201 (18) ◽  
Author(s):  
Nina I. Sulkowski ◽  
Gail G. Hardy ◽  
Yves V. Brun ◽  
Tanmay A. M. Bharat
Keyword(s):  
Cell Surface ◽  
Outer Membrane ◽  
Biofilm Formation ◽  
Caulobacter Crescentus ◽  
Cell Envelope ◽  
Bacterial Colonization ◽  
Bacterial Species ◽  
Specific Cell ◽  
Content Type ◽  
In Cells

ABSTRACTAdhesion allows microbes to colonize surfaces and is the first stage in biofilm formation. Stable attachment of the freshwater alphaproteobacteriumCaulobacter crescentusto surfaces requires an adhesive polysaccharide called holdfast, which is synthesized at a specific cell pole and ultimately found at the tip of cylindrical extensions of the cell envelope called stalks. Secretion and anchoring of holdfast to the cell surface are governed by proteins HfsDAB and HfaABD, respectively. The arrangement and organization of these proteins with respect to each other and the cell envelope, and the mechanism by which the holdfast is anchored on cells, are unknown. In this study, we have imaged a series ofC. crescentusmutants using electron cryotomography, revealing the architecture and arrangement of the molecular machinery involved in holdfast anchoring in cells. We found that the holdfast is anchored to cells by a defined complex made up of the HfaABD proteins and that the HfsDAB secretion proteins are essential for proper assembly and localization of the HfaABD anchor. Subtomogram averaging of cell stalk tips showed that the HfaABD complex spans the outer membrane. The anchor protein HfaB is the major component of the anchor complex located on the periplasmic side of the outer membrane, while HfaA and HfaD are located on the cell surface. HfaB is the critical component of the complex, without which no HfaABD complex was observed in cells. These results allow us to propose a working model of holdfast anchoring, laying the groundwork for further structural and cell biological investigations.IMPORTANCEAdhesion and biofilm formation are fundamental processes that accompany bacterial colonization of surfaces, which are of critical importance in many infections.Caulobacter crescentusbiofilm formation proceeds via irreversible adhesion mediated by a polar polysaccharide called holdfast. Mechanistic and structural details of how the holdfast is secreted and anchored on cells are still lacking. Here, we have assigned the location and described the arrangement of the holdfast anchor complex. This work increases our knowledge of the relatively underexplored field of polysaccharide-mediated adhesion by identifying structural elements that anchor polysaccharides to the cell envelope, which is important in a variety of bacterial species.

scholarly journals The Helicobacter pylori Autotransporter ImaA (HP0289) Modulates the Immune Response and Contributes to Host Colonization

2012 ◽  
Vol 80 (7) ◽  
pp. 2286-2296 ◽  
Author(s):  
William E. Sause ◽  
Andrea R. Castillo ◽  
Karen M. Ottemann
Keyword(s):  
Immune Response ◽  
Helicobacter Pylori ◽  
Membrane Protein ◽  
Outer Membrane ◽  
Outer Membrane Protein ◽  
Dependent Manner ◽  
Wild Type ◽  
Content Type ◽  
H Pylori ◽  
Murine Infections

ABSTRACTThe human pathogenHelicobacter pyloriemploys a diverse collection of outer membrane proteins to colonize, persist, and drive disease within the acidic gastric environment. In this study, we sought to elucidate the function of the host-induced geneHP0289, which encodes an uncharacterized outer membrane protein. We first generated an isogenicH. pylorimutant that lacksHP0289and found that the mutant has a colonization defect in single-strain infections and is greatly outcompeted in mouse coinfection experiments with wild-typeH. pylori. Furthermore, we used protease assays and biochemical fractionation coupled with an HP0289-targeted peptide antibody to verify that the HP0289 protein resides in the outer membrane. Our previous findings showed that theHP0289promoter is upregulated in the mouse stomach, and here we demonstrate thatHP0289expression is induced under acidic conditions in an ArsRS-dependent manner. Finally, we have shown that theHP0289mutant induces greater expression of the chemokine interleukin-8 (IL-8) and the cytokine tumor necrosis factor alpha (TNF-α) in gastric carcinoma cells (AGS). Similarly, transcription of the IL-8 homolog keratinocyte-derived chemokine (KC) is elevated in murine infections with the HP0289 mutant than in murine infections with wild-typeH. pylori. On the basis of this phenotype, we renamed HP0289 ImaA forimmunomodulatoryautotransporter protein. Our work has revealed that genes inducedin vivoplay an important role inH. pyloripathogenesis. Specifically, the outer membrane protein ImaA modulates a component of the host inflammatory response, and thus may allowH. pylorito fine tune the host immune response based on ImaA expression.

scholarly journals Neurons Are Host Cells for Mycobacterium tuberculosis

2014 ◽  
Vol 82 (5) ◽  
pp. 1880-1890 ◽  
Author(s):  
Philippa J. Randall ◽  
Nai-Jen Hsu ◽  
Dirk Lang ◽  
Susan Cooper ◽  
Boipelo Sebesho ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Mycobacterium Tuberculosis ◽  
Host Cells ◽  
Productive Infection ◽  
Target Cells ◽  
Dependent Manner ◽  
Content Type ◽  
The Central Nervous System

ABSTRACTMycobacterium tuberculosisinfection of the central nervous system is thought to be initiated once the bacilli have breached the blood brain barrier and are phagocytosed, primarily by microglial cells. In this study, the interactions ofM. tuberculosiswith neuronsin vitroandin vivowere investigated. The data obtained demonstrate that neurons can act as host cells forM. tuberculosis.M. tuberculosisbacilli were internalized by murine neuronal cultured cells in a time-dependent manner after exposure, with superior uptake by HT22 cells compared to Neuro-2a cells (17.7% versus 9.8%). Internalization ofM. tuberculosisbacilli by human SK-N-SH cultured neurons suggested the clinical relevance of the findings. Moreover, primary murine hippocampus-derived neuronal cultures could similarly internalizeM. tuberculosis. InternalizedM. tuberculosisbacilli represented a productive infection with retention of bacterial viability and replicative potential, increasing 2- to 4-fold within 48 h.M. tuberculosisbacillus infection of neurons was confirmedin vivoin the brains of C57BL/6 mice after intracerebral challenge. This study, therefore, demonstrates neurons as potential new target cells forM. tuberculosiswithin the central nervous system.

scholarly journals Pushing beyond the Envelope: the Potential Roles of OprF inPseudomonas aeruginosaBiofilm Formation and Pathogenicity

2019 ◽  
Vol 201 (18) ◽  
Author(s):  
Erin K. Cassin ◽  
Boo Shan Tseng
Keyword(s):  
Extracellular Matrix ◽  
Outer Membrane ◽  
Biofilm Formation ◽  
Matrix Protein ◽  
Cell Envelope ◽  
Outer Membrane Vesicles ◽  
Extracellular Dna ◽  
Future Research ◽  
Content Type ◽  
Biofilm Matrix

ABSTRACTThe ability ofPseudomonas aeruginosato form biofilms, which are communities of cells encased in a self-produced extracellular matrix, protects the cells from antibiotics and the host immune response. While some biofilm matrix components, such as exopolysaccharides and extracellular DNA, are relatively well characterized, the extracellular matrix proteins remain understudied. Multiple proteomic analyses of theP. aeruginosasoluble biofilm matrix and outer membrane vesicles, which are a component of the matrix, have identified OprF as an abundant matrix protein. To date, the few reports on the effects ofoprFmutations on biofilm formation are conflicting, and little is known about the potential role of OprF in the biofilm matrix. The majority of OprF studies focus on the protein as a cell-associated porin. As a component of the outer membrane, OprF assumes dual conformations and is involved in solute transport, as well as cell envelope integrity. Here, we review the current literature on OprF inP. aeruginosa, discussing how the structure and function of the cell-associated and matrix-associated protein may affect biofilm formation and pathogenesis in order to inform future research on this understudied matrix protein.

scholarly journals A New Family of Membrane Electron Transporters and Its Substrates, Including a New Cell Envelope Peroxiredoxin, Reveal a Broadened Reductive Capacity of the Oxidative Bacterial Cell Envelope

mBio ◽  
2012 ◽  
Vol 3 (2) ◽  
Author(s):  
Seung-Hyun Cho ◽  
Derek Parsonage ◽  
Casey Thurston ◽  
Rachel J. Dutton ◽  
Leslie B. Poole ◽  
...  
Keyword(s):  
Bacterial Cell ◽  
Protein Disulfide Isomerase ◽  
Caulobacter Crescentus ◽  
Cell Envelope ◽  
Content Type ◽  
Disulfide Isomerase ◽  
Bacterial Cell Envelope ◽  
Peroxide Reduction ◽  
Protein Disulfide ◽  
Novel Protein

ABSTRACTTheEscherichia colimembrane protein DsbD functions as an electron hub that dispatches electrons received from the cytoplasmic thioredoxin system to periplasmic oxidoreductases involved in protein disulfide isomerization, cytochromecbiogenesis, and sulfenic acid reduction. Here, we describe a new class of DsbD proteins, named ScsB, whose members are found in proteobacteria andChlamydia. ScsB has a domain organization similar to that of DsbD, but its amino-terminal domain differs significantly. In DsbD, this domain directly interacts with substrates to reduce them, which suggests that ScsB acts on a different array of substrates. UsingCaulobacter crescentusas a model organism, we searched for the substrates of ScsB. We discovered that ScsB provides electrons to the first peroxide reduction pathway identified in the bacterial cell envelope. The reduction pathway comprises a thioredoxin-like protein, TlpA, and a peroxiredoxin, PprX. We show that PprX is a thiol-dependent peroxidase that efficiently reduces both hydrogen peroxide and organic peroxides. Moreover, we identified two additional proteins that depend on ScsB for reduction, a peroxiredoxin-like protein, PrxL, and a novel protein disulfide isomerase, ScsC. Altogether, our results reveal that the array of proteins involved in reductive pathways in the oxidative cell envelope is significantly broader than was previously thought. Moreover, the identification of a new periplasmic peroxiredoxin indicates that in some bacteria, it is important to directly scavenge peroxides in the cell envelope even before they reach the cytoplasm.IMPORTANCEPeroxides are reactive oxygen species (ROS) that damage cellular components such as lipids, proteins, and nucleic acids. The presence of protection mechanisms against ROS is essential for cell survival. Bacteria express cytoplasmic catalases and thiol-dependent peroxidases to directly scavenge harmful peroxides. We report the identification of a peroxide reduction pathway active in the periplasm ofCaulobacter crescentus, which reveals that, in some bacteria, it is important to directly scavenge peroxides in the cell envelope even before they reach the cytoplasm. The electrons required for peroxide reduction are delivered to this pathway by ScsB, a new type of membrane electron transporter. We also identified two additional likely ScsB substrates, including a novel protein disulfide isomerase. Our results reveal that the array of proteins involved in reductive pathways in the oxidative environment of the cell envelope is significantly broader than was previously thought.

scholarly journals Evolution of Mycolic Acid Biosynthesis Genes and Their Regulation during Starvation in Mycobacterium tuberculosis

2015 ◽  
Vol 197 (24) ◽  
pp. 3797-3811 ◽  
Author(s):  
Stevie Jamet ◽  
Yves Quentin ◽  
Coralie Coudray ◽  
Pauline Texier ◽  
Françoise Laval ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Outer Membrane ◽  
Cell Envelope ◽  
Stringent Response ◽  
Mycolic Acid ◽  
Content Type ◽  
New Targets ◽  
Key Enzyme ◽  
Unique Cell ◽  
Translational Apparatus

ABSTRACTMycobacterium tuberculosis, the etiological agent of tuberculosis, is a Gram-positive bacterium with a unique cell envelope composed of an essential outer membrane. Mycolic acids, which are very-long-chain (up to C100) fatty acids, are the major components of this mycomembrane. The enzymatic pathways involved in the biosynthesis and transport of mycolates are fairly well documented and are the targets of the major antituberculous drugs. In contrast, only fragmented information is available on the expression and regulation of the biosynthesis genes. In this study, we report that thehadA,hadB, andhadCgenes, which code for the mycolate biosynthesis dehydratase enzymes, are coexpressed with three genes that encode proteins of the translational apparatus. Consistent with the well-established control of the translation potential by nutrient availability, starvation leads to downregulation of thehadABCgenes along with most of the genes required for the synthesis, modification, and transport of mycolates. The downregulation of a subset of the biosynthesis genes is partially dependent on RelMtb, the key enzyme of the stringent response. We also report the phylogenetic evolution scenario that has shaped the current genetic organization, characterized by the coregulation of thehadABCoperon with genes of the translational apparatus and with genes required for the modification of the mycolates.IMPORTANCEMycobacterium tuberculosisinfects one-third of the human population worldwide, and despite the available therapeutic arsenal, it continues to kill millions of people each year. There is therefore an urgent need to identify new targets and develop a better understanding of how the bacterium is adapting itself to host defenses during infection. A prerequisite of this understanding is knowledge of how this adaptive skill has been implanted by evolution. Nutrient scarcity is an environmental condition the bacterium has to cope with during infection. In many bacteria, adaptation to starvation relies partly on the stringent response.M. tuberculosis's unique outer membrane layer, the mycomembrane, is crucial for its viability and virulence. Despite its being the target of the major antituberculosis drugs, only scattered information exists on how the genes required for biosynthesis of the mycomembrane are expressed and regulated during starvation. This work has addressed this issue as a step toward the identification of new targets in the fight againstM. tuberculosis.

scholarly journals Extracellular gluco-oligosaccharide degradation by Caulobacter crescentus

Microbiology ◽  
2014 ◽  
Vol 160 (3) ◽  
pp. 635-645 ◽  
Author(s):  
Gerald N. Presley ◽  
Matthew J. Payea ◽  
Logan R. Hurst ◽  
Annie E. Egan ◽  
Brandon S. Martin ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Organic Molecules ◽  
Caulobacter Crescentus ◽  
Nutrient Transport ◽  
Proton Motive Force ◽  
Facilitated Diffusion ◽  
Extracellular Medium ◽  
Oligotrophic Bacterium ◽  
Carbonyl Cyanide ◽  
Dependent Transport

The oligotrophic bacterium Caulobacter crescentus has the ability to metabolize various organic molecules, including plant structural carbohydrates, as a carbon source. The nature of β-glucosidase (BGL)-mediated gluco-oligosaccharide degradation and nutrient transport across the outer membrane in C. crescentus was investigated. All gluco-oligosaccharides tested (up to celloheptose) supported growth in M2 minimal media but not cellulose or CM-cellulose. The periplasmic and outer membrane fractions showed highest BGL activity, but no significant BGL activity was observed in the cytosol or extracellular medium. Cells grown in cellobiose showed expression of specific BGLs and TonB-dependent receptors (TBDRs). Carbonyl cyanide 3-chlorophenylhydrazone lowered the rate of cell growth in cellobiose but not in glucose, indicating potential cellobiose transport into the cell by a proton motive force-dependent process, such as TBDR-dependent transport, and facilitated diffusion of glucose across the outer membrane via specific porins. These results suggest that C. crescentus acquires carbon from cellulose-derived gluco-oligosaccharides found in the environment by extracellular and periplasmic BGL activity and TBDR-mediated transport. This report on extracellular degradation of gluco-oligosaccharides and methods of nutrient acquisition by C. crescentus supports a broader suite of carbohydrate metabolic capabilities suggested by the C. crescentus genome sequence that until now have not been reported.

scholarly journals Suppressor Analysis of the Fusogenic Lambda Spanins

2017 ◽  
Vol 91 (14) ◽  
Author(s):  
Jesse Cahill ◽  
Manoj Rajaure ◽  
Ashley Holt ◽  
Russell Moreland ◽  
Chandler O'Leary ◽  
...  
Keyword(s):  
Genetic Analysis ◽  
Membrane Fusion ◽  
Cell Envelope ◽  
Coiled Coil ◽  
Class I ◽  
Intermediate Structure ◽  
Content Type ◽  
Outer Membranes ◽  
Fusion Systems ◽  
Suppressor Analysis

ABSTRACT The final step of lysis in phage λ infections of Escherichia coli is mediated by the spanins Rz and Rz1. These proteins form a complex that bridges the cell envelope and that has been proposed to cause fusion of the inner and outer membranes. Accordingly, mutations that block spanin function are found within coiled-coil domains and the proline-rich region, motifs essential in other fusion systems. To gain insight into spanin function, pseudorevertant alleles that restored plaque formation for lysis-defective mutants of Rz and Rz1 were selected. Most second-site suppressors clustered within a coiled-coil domain of Rz near the outer leaflet of the cytoplasmic membrane and were not allele specific. Suppressors largely encoded polar insertions within the hydrophobic core of the coiled-coil interface. Such suppressor changes resulted in decreased proteolytic stability of the Rz double mutants in vivo. Unlike the wild type, in which lysis occurs while the cells retain a rod shape, revertant alleles with second-site suppressor mutations supported lysis events that were preceded by spherical cell formation. This suggests that destabilization of the membrane-proximal coiled coil restores function for defective spanin alleles by increasing the conformational freedom of the complex at the cost of its normal, all-or-nothing functionality. IMPORTANCE Caudovirales encode cell envelope-spanning proteins called spanins, which are thought to fuse the inner and outer membranes during phage lysis. Recent genetic analysis identified the functional domains of the lambda spanins, which are similar to class I viral fusion proteins. While the pre- and postfusion structures of model fusion systems have been well characterized, the intermediate structure(s) formed during the fusion reaction remains elusive. Genetic analysis would be expected to identify functional connections between intermediates. Since most membrane fusion systems are not genetically tractable, only few such investigations have been reported. Here, we report a suppressor analysis of lambda spanin function. To our knowledge this is the first suppression analysis of a class I-like complex and also the first such analysis of a prokaryote membrane fusion system.

scholarly journals Appropriate Regulation of the σE-Dependent Envelope Stress Response Is Necessary To Maintain Cell Envelope Integrity and Stationary-Phase Survival in Escherichia coli

2017 ◽  
Vol 199 (12) ◽  
Author(s):  
Hervé Nicoloff ◽  
Saumya Gopalkrishnan ◽  
Sarah E. Ades
Keyword(s):  
Escherichia Coli ◽  
Stationary Phase ◽  
Outer Membrane ◽  
Stress Responses ◽  
Cell Envelope ◽  
Membrane Integrity ◽  
Point Mutations ◽  
Content Type ◽  
Envelope Stress ◽  
Outer Membrane Porins

ABSTRACT The alternative sigma factor σE is a key component of the Escherichia coli response to cell envelope stress and is required for viability even in the absence of stress. The activity of σE increases during entry into stationary phase, suggesting an important role for σE when nutrients are limiting. Elevated σE activity has been proposed to activate a pathway leading to the lysis of nonculturable cells that accumulate during early stationary phase. To better understand σE-directed cell lysis and the role of σE in stationary phase, we investigated the effects of elevated σE activity in cultures grown for 10 days. We demonstrate that high σE activity is lethal for all cells in stationary phase, not only those that are nonculturable. Spontaneous mutants with reduced σE activity, due primarily to point mutations in the region of σE that binds the −35 promoter motif, arise and take over cultures within 5 to 6 days after entry into stationary phase. High σE activity leads to large reductions in the levels of outer membrane porins and increased membrane permeability, indicating membrane defects. These defects can be counteracted and stationary-phase lethality delayed significantly by stabilizing membranes with Mg2+ and buffering the growth medium or by deleting the σE-dependent small RNAs (sRNAs) MicA, RybB, and MicL, which inhibit the expression of porins and Lpp. Expression of these sRNAs also reverses the loss of viability following depletion of σE activity. Our results demonstrate that appropriate regulation of σE activity, ensuring that it is neither too high nor too low, is critical for envelope integrity and cell viability. IMPORTANCE The Gram-negative cell envelope and cytoplasm differ significantly, and separate responses have evolved to combat stress in each compartment. An array of cell envelope stress responses exist, each of which is focused on different parts of the envelope. The σE response is conserved in many enterobacteria and is tuned to monitor pathways for the maturation and delivery of outer membrane porins, lipoproteins, and lipopolysaccharide to the outer membrane. The activity of σE is tightly regulated to match the production of σE regulon members to the needs of the cell. In E. coli, loss of σE results in lethality. Here we demonstrate that excessive σE activity is also lethal and results in decreased membrane integrity, the very phenotype the system is designed to prevent.

scholarly journals DpaA Detaches Braun’s Lipoprotein from Peptidoglycan

mBio ◽  
2021 ◽  
Vol 12 (3) ◽  
Author(s):  
Matthias Winkle ◽  
Víctor M. Hernández-Rocamora ◽  
Karthik Pullela ◽  
Emily C. A. Goodall ◽  
Alessandra M. Martorana ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Cell Envelope ◽  
Stress Conditions ◽  
Permeability Barrier ◽  
Gram Negative Bacteria ◽  
Sequence Motifs ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Impermeable Barrier

ABSTRACT Gram-negative bacteria have a unique cell envelope with a lipopolysaccharide-containing outer membrane that is tightly connected to a thin layer of peptidoglycan. The tight connection between the outer membrane and peptidoglycan is needed to maintain the outer membrane as an impermeable barrier for many toxic molecules and antibiotics. Enterobacteriaceae such as Escherichia coli covalently attach the abundant outer membrane-anchored lipoprotein Lpp (Braun’s lipoprotein) to tripeptides in peptidoglycan, mediated by the transpeptidases LdtA, LdtB, and LdtC. LdtD and LdtE are members of the same family of ld-transpeptidases but they catalyze a different reaction, the formation of 3-3 cross-links in the peptidoglycan. The function of the sixth homologue in E. coli, LdtF, remains unclear, although it has been shown to become essential in cells with inhibited lipopolysaccharide export to the outer membrane. We now show that LdtF hydrolyzes the Lpp-peptidoglycan linkage, detaching Lpp from peptidoglycan, and have renamed LdtF to peptidoglycan meso-diaminopimelic acid protein amidase A (DpaA). We show that the detachment of Lpp from peptidoglycan is beneficial for the cell under certain stress conditions and that the deletion of dpaA allows frequent transposon inactivation in the lapB (yciM) gene, whose product downregulates lipopolysaccharide biosynthesis. DpaA-like proteins have characteristic sequence motifs and are present in many Gram-negative bacteria, of which some have no Lpp, raising the possibility that DpaA has other substrates in these species. Overall, our data show that the Lpp-peptidoglycan linkage in E. coli is more dynamic than previously appreciated. IMPORTANCE Gram-negative bacteria have a complex cell envelope with two membranes and a periplasm containing the peptidoglycan layer. The outer membrane is firmly connected to the peptidoglycan by highly abundant proteins. The outer membrane-anchored Braun’s lipoprotein (Lpp) is the most abundant protein in E. coli, and about one-third of the Lpp molecules become covalently attached to tripeptides in peptidoglycan. The attachment of Lpp to peptidoglycan stabilizes the cell envelope and is crucial for the outer membrane to function as a permeability barrier for a range of toxic molecules and antibiotics. So far, the attachment of Lpp to peptidoglycan has been considered to be irreversible. We have now identified an amidase, DpaA, which is capable of detaching Lpp from peptidoglycan, and we show that the detachment of Lpp is important under certain stress conditions. DpaA-like proteins are present in many Gram-negative bacteria and may have different substrates in these species.

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