lfnA from Pseudomonas aeruginosa O12 and wbuX from Escherichia coli O145 encode membrane-associated proteins and are required for expression of 2,6-dideoxy-2-acetamidino-L-galactose in lipopolysaccharide O antigen

Thioglycosides Act as Metabolic Inhibitors of Bacterial Glycan Biosynthesis

Glycans that coat the surface of bacteria are compelling antibiotic targets because they contain distinct monosaccharides that are linked to pathogenesis and are absent in human cells. Disrupting glycan biosynthesis presents a path to inhibiting the ability of a bacterium to infect the host. We previously demonstrated that O-glycosides act as metabolic inhibitors and disrupt bacterial glycan biosynthesis. Inspired by a recent study which showed that thioglycosides (S-glycosides) are 10 times more effective than O-glycosides at inhibiting glycan biosynthesis in mammalian cells, we crafted a panel of S-glycosides based on rare bacterial monosaccharides. The novel thioglycosides altered glycan biosynthesis and fitness in pathogenic bacteria but had no notable effect on glycosylation or growth in beneficial bacteria or mammalian cells. In contrast to findings in mammalian cells, S-glycosides and O-glycosides exhibited comparable potency in bacteria. However, S-glycosides exhibited enhanced selectivity relative to O-glycosides. These novel metabolic inhibitors will allow selective perturbation of the bacterial glycocalyx for functional studies and set the stage to expand our antibiotic arsenal.

Synthesis and Application of Rare Deoxy Amino l-Sugar Analogues to Probe Glycans in Pathogenic Bacteria

Bacterial cell envelope glycans are compelling antibiotic targets as they are critical for strain fitness and pathogenesis yet are virtually absent from human cells. However, systematic study and perturbation of bacterial glycans remains challenging due to their utilization of rare deoxy amino l-sugars, which impede traditional glycan analysis and are not readily available from natural sources. The development of chemical tools to study bacterial glycans is a crucial step toward understanding and altering these biomolecules. Here we report an expedient methodology to access azide-containing analogues of a variety of unusual deoxy amino l-sugars starting from readily available l-rhamnose and l-fucose. Azide-containing l-sugar analogues facilitated metabolic profiling of bacterial glycans in a range of Gram-negative bacteria and revealed differential utilization of l-sugars in symbiotic versus pathogenic bacteria. Further application of these probes will refine our knowledge of the glycan repertoire in diverse bacteria and aid in the design of novel antibiotics.

Participation of Acyl-Coenzyme A Synthetase FadD4 of Pseudomonas aeruginosa PAO1 in Acyclic Terpene/Fatty Acid Assimilation and Virulence by Lipid A Modification

The pathogenic bacterium Pseudomonas aeruginosa possesses high metabolic versatility, with its effectiveness to cause infections likely due to its well-regulated genetic content. P. aeruginosa PAO1 has at least six fadD paralogous genes, which have been implicated in fatty acid (FA) degradation and pathogenicity. In this study, we used mutagenesis and a functional approach in P. aeruginosa PAO1 to determine the roles of the fadD4 gene in acyclic terpene (AT) and FA assimilation and on pathogenicity. The results indicate that fadD4 encodes a terpenoyl-CoA synthetase utilized for AT and FA assimilation. Additionally, mutations in fadD paralogs led to the modification of the quorum-sensing las/rhl systems, as well as the content of virulence factors pyocyanin, biofilm, rhamnolipids, lipopolysaccharides (LPS), and polyhydroxyalkanoates. In a Caenorhabditis elegans in vivo pathogenicity model, culture supernatants from the 24-h-grown fadD4 single mutant increased lethality compared to the PAO1 wild-type (WT) strain; however, the double mutants fadD1/fadD2, fadD1/fadD4, and fadD2/fadD4 and single mutant fadD2 increased worm survival. A correlation analysis indicated an interaction between worm death by the PAO1 strain, the fadD4 mutation, and the virulence factor LPS. Fatty acid methyl ester (FAME) analysis of LPS revealed that a proportion of the LPS and FA on lipid A were modified by the fadD4 mutation, suggesting that FadD4 is also involved in the synthesis/degradation and modification of the lipid A component of LPS. LPS isolated from the fadD4 mutant and double mutants fadD1/fadD4 and fadD2/fadD4 showed a differential behavior to induce an increase in body temperature in rats injected with LPS compared to the WT strain or from the fadD1 and fadD2 mutants. In agreement, LPS isolated from the fadD4 mutant and double mutants fadD1/fadD2 and fadD2/fadD4 increased the induction of IL-8 in rat sera, but IL1-β cytokine levels decreased in the double mutants fadD1/fadD2 and fadD1/fadD4. The results indicate that the fadD genes are implicated in the degree of pathogenicity of P. aeruginosa PAO1 induced by LPS-lipid A, suggesting that FadD4 contributes to the removal of acyl-linked FA from LPS, rendering modification in its immunogenic response associated to Toll-like receptor TLR4. The genetic redundancy of fadD is important for bacterial adaptability and pathogenicity over the host.

Characterization of the First Bacterial and Thermostable GDP-Mannose 3,5-Epimerase

GDP-mannose 3,5-epimerase (GM35E) catalyzes the conversion of GDP-mannose towards GDP-l-galactose and GDP-l-gulose. Although this reaction represents one of the few enzymatic routes towards the production of l-sugars and derivatives, it has not yet been exploited for that purpose. One of the reasons is that so far only GM35Es from plants have been characterized, yielding biocatalysts that are relatively unstable and difficult to express heterologously. Through the mining of sequence databases, we succeeded in identifying a promising bacterial homologue. The gene from the thermophilic organism Methylacidiphilum fumariolicum was codon optimized for expression in Escherichia coli, resulting in the production of 40 mg/L of recombinant protein. The enzyme was found to act as a self-sufficient GM35E, performing three chemical reactions in the same active site. Furthermore, the biocatalyst was highly stable at temperatures up to 55 °C, making it well suited for the synthesis of new carbohydrate products with application in the pharma industry.

Unique Regions of the Polysaccharide Copolymerase Wzz2 from Pseudomonas aeruginosa Are Essential for O-Specific Antigen Chain Length Control

The outer leaflet of the outer membrane of nearly all Gram-negative bacteria contains lipopolysaccharide (LPS). The distal end of LPS may be capped with O antigen, a long polysaccharide that can range from a few to hundreds of sugars in length. The chain length of the polysaccharide has many implications for bacterial survival and consequently is tightly controlled. In the Wzx/Wzy-dependent route of O antigen synthesis, one or more Wzz proteins determine the chain length via an unknown mechanism. To gain insight into this mechanism, we identified and characterized important regions of two Wzz proteins in Pseudomonas aeruginosa serotype O13, which confer the production of "long" (Wzz₁) and "very long" (Wzz₂) chain lengths, respectively. We found that compared to Wzz₁, Wzz₂ has distinct amino acid insertions in the central α-helices (ins_α6 and ins_α7) and in membrane-distal (ins_L4) and -proximal (ins_IL) loops. When these regions were deleted in Wzz₂, the mutant proteins conferred drastically shortened chain lengths. Within these regions we identified several conserved amino acid residues that were then targeted for site-directed mutagenesis. Our results implicate an RTE motif in loop 4 and a "hot spot" of charged and polar residues in ins_α7 in the function of Wzz₂ We present evidence that the functionally important residues of ins_α7 are likely involved in stabilizing Wzz through coiled-coil interactions.IMPORTANCE O antigen is an important virulence factor presented on the cell surface of Gram-negative bacteria that is critical for bacterial physiology and pathogenesis. However, some aspects of O antigen biosynthesis, such as the mechanisms for determining polysaccharide chain length, are poorly understood. In this study, we identified unique regions in the O antigen chain length regulators (termed Wzz) of the problematic opportunistic pathogen Pseudomonas aeruginosa We show that these regions are critical for determining O antigen chain length, which provides new insight into the model of the Wzz mechanism. Ultimately, our work adds knowledge toward understanding an important step in the biosynthesis of this virulence factor, which is applicable to a wide range of Gram-negative pathogens.

Overexpression of O-polysaccharide chain length regulators in Gram-negative bacteria using the Wzx-/Wzy-dependent pathway enhances production of defined modal length O-polysaccharide polymers for use as haptens in glycoconjugate vaccines

Aims

O‐polysaccharide (OPS) molecules are protective antigens for several bacterial pathogens, and have broad utility as components of glycoconjugate vaccines. Variability in the OPS chain length is one obstacle towards further development of these vaccines. Introduction of sizing steps during purification of OPS molecules of suboptimal or of mixed lengths introduces additional costs and complexity while decreasing the final yield. The overall goal of this study was to demonstrate the utility of engineering Gram‐negative bacteria to produce homogenous O‐polysaccharide populations that can be used as the basis of carbohydrate vaccines by overexpressing O‐polysaccharide chain length regulators of the Wzx‐/Wzy‐dependent pathway.

Method and Results

The O‐polysaccharide chain length regulators wzzB and fepE from Salmonella Typhimurium I77 and wzz2 from Pseudomonas aeruginosa PAO1 were cloned and expressed in the homologous organism or in other Gram‐negative bacteria. Overexpression of these Wzz proteins in the homologous organism significantly increased the proportion of long or very long chain O‐polysaccharides. The same observation was made when wzzB was overexpressed in Salmonella Paratyphi A and Shigella flexneri, and wzz2 was overexpressed in two other strains of P. aeruginosa.

Conclusions

Overexpression of Wzz proteins in Gram‐negative bacteria using the Wzx/Wzy‐dependant pathway for lipopolysaccharide synthesis provides a genetic method to increase the production of an O‐polysaccharide population of a defined size.

Significance and Impact of the Study

The methods presented herein represent a cost‐effective and improved strategy for isolating preferred OPS vaccine haptens, and could facilitate the further use of O‐polysaccharides in glycoconjugate vaccine development.

Pseudomonas aeruginosa ExlA and Serratia marcescens ShlA trigger cadherin cleavage by promoting calcium influx and ADAM10 activation

Pore-forming toxins are potent virulence factors secreted by a large array of bacteria. Here, we deciphered the action of ExlA from Pseudomonas aeruginosa and ShlA from Serratia marcescens on host cell-cell junctions. ExlA and ShlA are two members of a unique family of pore-forming toxins secreted by a two-component secretion system. Bacteria secreting either toxin induced an ExlA- or ShlA-dependent rapid cleavage of E-cadherin and VE-cadherin in epithelial and endothelial cells, respectively. Cadherin proteolysis was executed by ADAM10, a host cell transmembrane metalloprotease. ADAM10 activation is controlled in the host cell by cytosolic Ca²⁺ concentration. We show that Ca²⁺ influx, induced by ExlA or ShlA pore formation in the plasma membrane, triggered ADAM10 activation, thereby leading to cadherin cleavage. Our data suggest that ADAM10 is not a cellular receptor for ExlA and ShlA, further confirming that ADAM10 activation occurred via Ca²⁺ signalling. In conclusion, ExlA- and ShlA-secreting bacteria subvert a regulation mechanism of ADAM10 to activate cadherin shedding, inducing intercellular junction rupture, cell rounding and loss of tissue barrier integrity.

Pore-forming toxins are the most widespread toxins delivered by pathogenic bacteria and are required for full virulence. Pore-forming toxins perforate membranes of host cells for intracellular delivery of bacterial factors, for bacterial escape from phagosomes or in order to kill cells. Loss of membrane integrity, especially the plasma membrane, has broad implications on cell and tissue physiology. Here, we show that two members of a unique family of pore-forming toxins, secreted by Pseudomonas aeruginosa and Serratia marcescens, have the capacity to disrupt cell-cell junctions of epithelial and endothelial cells, hence breaching two major tissue barriers.

Utilization of bench-stable and readily available nickel(II) triflate for access to 1,2-cis-2-aminoglycosides

The utilization of substoichiometric amounts of commercially available nickel(II) triflate as an activator in the reagent-controlled glycosylation reaction for the stereoselective construction of biologically relevant targets containing 1,2-cis-2-amino glycosidic linkages is reported. This straightforward and accessible methodology is mild, operationally simple and safe through catalytic activation by readily available Ni(OTf)₂ in comparison to systems employing our previously in-house prepared Ni(4-F-PhCN)₄(OTf)₂. We anticipate that the bench-stable and inexpensive Ni(OTf)₂, coupled with little to no extra laboratory training to set up the glycosylation reaction and no requirement of specialized equipment, should make this methodology be readily adopted by non-carbohydrate specialists. This report further highlights the efficacy of Ni(OTf)₂ to prepare several bioactive motifs, such as blood type A-type V and VI antigens, heparin sulfate disaccharide repeating unit, aminooxy glycosides, and α-GalNAc-Serine conjugate, which cannot be achieved in high yield and α-selectivity utilizing in-house prepared Ni(4-F-PhCN)₄(OTf)₂ catalyst. The newly-developed protocol eliminates the need for the synthesis of Ni(4-F-PhCN)₄(OTf)₂ and is scalable and reproducible. Furthermore, computational simulations in combination with ¹H NMR studies analyzed the effects of various solvents on the intramolecular hydrogen bonding network of tumor-associated mucin Fmoc-protected GalNAc-threonine amino acid antigen derivative, verifying discrepancies found that were previously unreported.

Phenotype and toxicity of the recently discovered exlA-positive Pseudomonas aeruginosa strains collected worldwide

We recently identified a hypervirulent strain of Pseudomonas aeruginosa, differing significantly from the classical strains in that it lacks the type 3 secretion system (T3SS), a major determinant of P. aeruginosa virulence. This new strain secretes a novel toxin, called ExlA, which induces plasma membrane rupture in host cells. For this study, we collected 18 other exlA-positive T3SS-negative strains, analyzed their main virulence factors and tested their toxicity in various models. Phylogenetic analysis revealed two groups. The strains were isolated on five continents from patients with various pathologies or in the environment. Their proteolytic activity and their motion abilities were highly different, as well as their capacity to infect epithelial, endothelial, fibroblastic and immune cells, which correlated directly with ExlA secretion levels. In contrast, their toxicity towards human erythrocytes was limited. Some strains were hypervirulent in a mouse pneumonia model and others on chicory leaves. We conclude that (i) exlA-positive strains can colonize different habitats and may induce various infection types, (ii) the strains secreting significant amounts of ExlA are cytotoxic for most cell types but are poorly hemolytic, (iii) toxicity in planta does not correlate with ExlA secretion.

Pseudomonas aeruginosa renews its virulence factors

Highly divergent strains of the major human opportunistic pathogen Pseudomonas aeruginosa have been isolated around the world by different research laboratories. They came from patients with various types of infectious diseases or from the environment. These strains are devoid of the major virulence factor used by classical strains, the Type III secretion system, but possess additional putative virulence factors, including a novel two-partner secretion system, ExlBA, responsible for the hypervirulent behavior of some clinical isolates. Here, we review the genetic and phenotypic characteristics of these recently-discovered P. aeruginosa outliers.

Monoclonal Antibodies to Lipopolysaccharide O Antigens of Enterohemorrhagic Escherichia coli Strains in Serogroups O26, O45, O103, O111, O121, and O145

Non-O157 enterohemorrhagic Escherichia coli in priority serogroups O26, O45, O103, O111, O121, and O145 are increasingly recognized as important human pathogens. In the present study, a panel of monoclonal antibodies (MAbs) to the lipopolysaccharide O antigens of E. coli in serogroups O26, O45, O103, O111, O121, and O145 was produced. The specificity was evaluated by examining the reactivity of the MAbs with 50 E. coli strains and 42 non-E. coli bacteria, and several MAbs highly specific for E. coli strains in each of the six non-O157 priority serogroups were identified. The use of these highly specific MAbs may be of considerable value for determining whether an E. coli isolate belongs to one of the six priority non-O157 serogroups, for developing specific detection assays for these organisms, and for characterizing the lipopolysaccharide O antigens of isolates in these serogroups.

Structural diversity in Salmonella O antigens and its genetic basis

This review covers the structures and genetics of the 46 O antigens of Salmonella, a major pathogen of humans and domestic animals. The variation in structures underpins the serological specificity of the 46 recognized serogroups. The O antigen is important for the full function and virulence of many bacteria, and the considerable diversity of O antigens can confer selective advantage. Salmonella O antigens can be divided into two major groups: those which have N-acetylglucosamine (GlcNAc) or N-acetylgalactosamine (GalNAc) and those which have galactose (Gal) as the first sugar in the O unit. In recent years, we have determined 21 chemical structures and sequenced 28 gene clusters for GlcNAc-/GalNAc-initiated O antigens, thus completing the structure and DNA sequence data for the 46 Salmonella O antigens. The structures and gene clusters of the GlcNAc-/GalNAc-initiated O antigens were found to be highly diverse, and 24 of them were found to be identical or closely related to Escherichia coli O antigens. Sequence comparisons indicate that all or most of the shared gene clusters were probably present in the common ancestor, although alternative explanations are also possible. In contrast, the better-known eight Gal-initiated O antigens are closely related both in structures and gene cluster sequences.

Identification of genes involved in the acetamidino group modification of the flagellin N-linked glycan of Methanococcus maripaludis

N-linked glycosylation of protein is a posttranslational modification found in all three domains of life. The flagellin proteins of the archaeon Methanococcus maripaludis are known to be modified with an N-linked tetrasaccharide consisting of N-acetylgalactosamine (GalNAc), a diacetylated glucuronic acid (GlcNAc3NAc), an acetylated and acetamidino-modified mannuronic acid with a substituted threonine group (ManNAc3NAmA6Thr), and a novel terminal sugar residue [(5S)-2-acetamido-2,4-dideoxy-5-O-methyl-α-L-erythro-hexos-5-ulo-1,5-pyranose]. To identify genes involved in biosynthesis of the component sugars of this glycan, three genes, mmp1081, mmp1082, and mmp1083, were targeted for in-frame deletion, based on their annotation and proximity to glycosyltransferase genes known to be involved in assembly of the glycan. Mutants carrying a deletion in any of these three genes remained flagellated and motile. A strain with a deletion of mmp1081 had lower-molecular-mass flagellins in Western blots. Mass spectrometry of purified flagella revealed a truncated glycan with the terminal sugar absent and the threonine residue and the acetamidino group missing from the third sugar. No glycan modification was seen in either the Δmmp1082 or Δmmp1083 mutant grown in complex Balch III medium. However, a glycan identical to the Δmmp1081 glycan was observed when the Δmmp1082 or Δmmp1083 mutant was grown under ammonia-limited conditions. We hypothesize that MMP1082 generates ammonia and tunnels it through MMP1083 to MMP1081, which acts as the amidotransferase, modifying the third sugar residue of the M. maripaludis glycan with the acetamidino group.

Primary mechanisms mediating aminoglycoside resistance in the multidrug-resistant Pseudomonas aeruginosa clinical isolate PA7

The multiresistant taxonomic outlier Pseudomonas aeruginosa PA7 possesses the conserved efflux genes, mexXY; however these are linked to a unique gene encoding an outer membrane channel, dubbed oprA, that is absent in most P. aeruginosa strains. Using genetic knockouts and single copy chromosomal complementation, we showed that aminoglycoside resistance in PA7 is mediated in part by the MexXY-OprA pump, and intriguingly that MexXY in this strain can utilize either the OprA or OprM outer membrane channel, linked to the mexAB efflux genes. We also identified a small portion of the oprA gene immediately downstream of the mexY gene in PAO1, suggesting that non-PA7 P. aeruginosa strains might have possessed, but lost, the intact mexXY-oprA efflux pump locus. Consistent with this, most of a panel of serotype strains possessed the truncated oprA but the serotype O12 isolate had an intact mexXY-oprA locus, similar to PA7 and the related strain DSM 1128. We also showed that the mexZ repressor gene upstream of mexXY-oprA in PA7 is mutated, leading to overexpression of mexXY-oprA, using sequencing, homologous replacement and real-time quantitative reverse transcriptase PCR. Finally we assessed the contribution of MexXY and aminoglycoside modifying enzymes AAC together to resistance in PA7 and the AAC(6')-Iae-mediated amikacin-resistant clinical isolate IMCJ2.S1, concluding that the effect of the modifying enzymes is enhanced by functional efflux, especially in the presence of divalent cations, to develop high-level aminoglycoside resistance in P. aeruginosa.

Biosynthesis of uronamide sugars in Pseudomonas aeruginosa O6 and Escherichia coli O121 O antigens

The major component of the outer leaflet of the outer membrane of Gram-negative bacteria is lipopolysaccharide (LPS). The outermost domain of LPS is a polysaccharide called O antigen. Pseudomonas aeruginosa establishes biofilms on wet surfaces in a wide range of habitats and mutations in O-antigen biosynthesis genes affect bacterial adhesion and the structure of these biofilms. The P. aeruginosa O6 O antigen contains a 2-acetamido-2-deoxy-d-galacturonamide (d-GalNAcAN) residue. O-antigen biosynthesis in this serotype requires the wbpS gene, which encodes a protein with conserved domains of the glutamine-dependent amidotransferase family. Replacement of conserved amino acids in the N-terminal glutaminase conserved domain of WbpS inhibited O-antigen biosynthesis under restricted-ammonia conditions, but not in rich media; suggesting that this domain functions to provide ammonia for O-antigen biosynthesis under restricted-ammonia conditions, by hydrolysis of glutamine. Escherichia coli O121 also produces a d-GalNAcAN-containing O antigen, and possesses a homologue of wbpS called wbqG. An E. coli O121 wbqG mutant was cross-complemented by providing wbpS in trans, and vice versa, showing that these two genes are functionally interchangeable. The E. coli O121 wbqG mutant O antigen contains 2-acetamido-2-deoxy-d-galacturonate (d-GalNAcA), instead of d-GalNAcAN, demonstrating that wbqG is specifically required for biosynthesis of the carboxamide in this sugar.

Review: Lipopolysaccharide biosynthesis in Pseudomonas aeruginosa

Pseudomonas aeruginosa causes serious nosocomial infections, and an important virulence factor produced by this organism is lipopolysaccharide (LPS). This review summarizes knowledge about biosynthesis of all three structural domains of LPS - lipid A, core oligosaccharide, and O polysaccharides. In addition, based on similarities with other bacterial species, this review proposes new hypothetical pathways for unstudied steps in the biosynthesis of P. aeruginosa LPS. Lipid A biosynthesis is discussed in relation to Escherichia coli and Salmonella, and the biosyntheses of core sugar precursors and core oligosaccharide are summarised. Pseudomonas aeruginosa attaches a Common Polysaccharide Antigen and O-Specific Antigen polysaccharides to lipid A-core. Both forms of O polysaccharide are discussed with respect to their independent synthesis mechanisms. Recent advances in understanding O-polysaccharide biosynthesis since the last major review on this subject, published nearly a decade ago, are highlighted. Since P. aeruginosa O polysaccharides contain unusual sugars, sugar-nucleotide biosynthesis pathways are reviewed in detail. Knowledge derived from detailed studies in the O5, O6 and O11 serotypes is applied to predict biosynthesis pathways of sugars in poorly-studied serotypes, especially O1, O4, and O13/O14. Although further work is required, a full understanding of LPS biosynthesis in P. aeruginosa is almost within reach.

Structure of O-antigen and functional characterization of O-antigen gene cluster of Salmonella enterica O47 containing ribitol phosphate and 2-acetimidoylamino-2,6-dideoxy-L-galactose

An O-polysaccharide was isolated by mild acid degradation of the lipopolysaccharide of Salmonella enterica O47 and studied by sugar analysis along with one- and two-dimensional 1H- and 13C-NMR spectroscopy. The following structure of the linear ribitol phosphate-containing repeating unit of the O-polysaccharide was established: -->2)-D-Ribitol-5-P-(O-->6)-alpha-D-Galp-(1-->3)-alpha-L-FucpNAm-(1-->3)-beta-D-GlcpNAc-(1-->, where FucNAm stands for 2-acetimidoylamino-2,6-dideoxy-L-galactose. About 10% of Gal is O-acetylated at position 4 and another minor O-acetyl group is present at an undetermined position. Functions of the S. enterica O47 antigen biosynthetic genes were tentatively assigned by comparison with gene databases and found to be in agreement with the O-polysaccharide structure. A comparison of the O-antigen gene clusters of S. enterica O47 and E. coli O145 suggested their close evolutionary relationship.

Post-assembly modification of Bordetella bronchiseptica O polysaccharide by a novel periplasmic enzyme encoded by wbmE

Bordetella bronchiseptica is a pathogen of humans and animals that colonizes the respiratory tract. It produces a lipopolysaccharide O antigen that contains a homopolymer of 2,3-dideoxy-2,3-diacetamido-l-galacturonic acid (l-GalNAc3NAcA). Some of these sugars are found in the uronamide form (l-GalNAc3NAcAN), and there is no discernible pattern in the distribution of amides along the chain. A B. bronchiseptica wbmE mutant expresses an O polysaccharide unusually rich in uronamides. The WbmE protein localizes to the periplasm and catalyzes the deamidation of uronamide-rich O chains in lipopolysaccharide purified from the mutant, to attain a wild-type uronamide/uronic acid ratio. WbmE is a member of the papain-like transglutaminase superfamily, and this categorization is consistent with a deamidase role. The periplasmic location of WbmE and its acceptance of complete lipopolysaccharide as substrate indicate that it operates at a late stage in lipopolysaccharide biosynthesis, after polymerization and export of the O chain from the cytoplasm. This is the first report of such a modification of O antigen after assembly. The expression of wbmE is controlled by the Bordetella virulence gene two-component regulatory system, BvgAS, suggesting that this deamidation is a novel mechanism by which these bacteria modify their cell surface charge in response to environmental stimuli.