Ght protein of Neisseria meningitidis is involved in the regulation of lipopolysaccharide biosynthesis

Regulated Expression of lpxC Allows for Reduction of Endotoxicity in Bordetella pertussis

The Gram-negative bacterium Bordetella pertussis is the causative agent of a respiratory infection known as whooping cough. Previously developed whole-cell pertussis vaccines were effective, but appeared to be too reactogenic mainly due to the presence of lipopolysaccharide (LPS, also known as endotoxin) in the outer membrane (OM). Here, we investigated the possibility of reducing endotoxicity by modulating the LPS levels. The promoter of the lpxC gene, which encodes the first committed enzyme in LPS biosynthesis, was replaced by an isopropyl β-D-1-thiogalactopyranoside (IPTG)-inducible promoter. The IPTG was essential for growth, even when the construct was moved into a strain that should allow for the replacement of LPS in the outer leaflet of the OM with phospholipids by defective phospholipid transporter Mla and OM phospholipase A. LpxC depletion in the absence of IPTG resulted in morphological changes of the cells and in overproduction of outer-membrane vesicles (OMVs). The reduced amounts of LPS in whole-cell preparations and in isolated OMVs of LpxC-depleted cells resulted in lower activation of Toll-like receptor 4 in HEK-Blue reporter cells. We suggest that, besides lipid A engineering, also a reduction in LPS synthesis is an attractive strategy for the production of either whole-cell- or OMV-based vaccines, with reduced reactogenicity for B. pertussis and other Gram-negative bacteria.

Acclimation to Nutritional Immunity and Metal Intoxication Requires Zinc, Manganese, and Copper Homeostasis in the Pathogenic Neisseriae

Neisseria gonorrhoeae and Neisseria meningitidis are human-specific pathogens in the Neisseriaceae family that can cause devastating diseases. Although both species inhabit mucosal surfaces, they cause dramatically different diseases. Despite this, they have evolved similar mechanisms to survive and thrive in a metal-restricted host. The human host restricts, or overloads, the bacterial metal nutrient supply within host cell niches to limit pathogenesis and disease progression. Thus, the pathogenic Neisseria require appropriate metal homeostasis mechanisms to acclimate to such a hostile and ever-changing host environment. This review discusses the mechanisms by which the host allocates and alters zinc, manganese, and copper levels and the ability of the pathogenic Neisseria to sense and respond to such alterations. This review will also discuss integrated metal homeostasis in N. gonorrhoeae and the significance of investigating metal interplay.

Border Control: Regulating LPS Biogenesis

The outer membrane (OM) is a defining feature of Gram-negative bacteria that serves as a permeability barrier and provides rigidity to the cell. Critical to OM function is establishing and maintaining an asymmetrical bilayer structure with phospholipids in the inner leaflet and the complex glycolipid lipopolysaccharide (LPS) in the outer leaflet. Cells ensure this asymmetry by regulating the biogenesis of lipid A, the conserved and essential anchor of LPS. Here we review the consequences of disrupting the regulatory components that control lipid A biogenesis, focusing on the rate-limiting step performed by LpxC. Dissection of these processes provides critical insights into bacterial physiology and potential new targets for antibiotics able to overcome rapidly spreading resistance mechanisms.

Regulated Assembly of LPS, Its Structural Alterations and Cellular Response to LPS Defects

Distinguishing feature of the outer membrane (OM) of Gram-negative bacteria is its asymmetry due to the presence of lipopolysaccharide (LPS) in the outer leaflet of the OM and phospholipids in the inner leaflet. Recent studies have revealed the existence of regulatory controls that ensure a balanced biosynthesis of LPS and phospholipids, both of which are essential for bacterial viability. LPS provides the essential permeability barrier function and act as a major virulence determinant. In Escherichia coli, more than 100 genes are required for LPS synthesis, its assembly at inner leaflet of the inner membrane (IM), extraction from the IM, translocation to the OM, and in its structural alterations in response to various environmental and stress signals. Although LPS are highly heterogeneous, they share common structural elements defining their most conserved hydrophobic lipid A part to which a core polysaccharide is attached, which is further extended in smooth bacteria by O-antigen. Defects or any imbalance in LPS biosynthesis cause major cellular defects, which elicit envelope responsive signal transduction controlled by RpoE sigma factor and two-component systems (TCS). RpoE regulon members and specific TCSs, including their non-coding arm, regulate incorporation of non-stoichiometric modifications of LPS, contributing to LPS heterogeneity and impacting antibiotic resistance.

Proteomics, Bioinformatics and Structure-Function Antigen Mining For Gonorrhea Vaccines

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the serious health consequences combined with the prevalence and the dire possibility of untreatable gonorrhea. Reverse vaccinology, which includes genome and proteome mining, has proven successful in the discovery of vaccine candidates against many pathogenic bacteria. Here, we describe proteomic applications including comprehensive, quantitative proteomic platforms and immunoproteomics coupled with broad-ranging bioinformatics that have been applied for antigen mining to develop gonorrhea vaccine(s). We further focus on outlining the vaccine candidate decision tree, describe the structure-function of novel proteome-derived antigens as well as ways to gain insights into their roles in the cell envelope, and underscore new lessons learned about the fascinating biology of Neisseria gonorrhoeae.

Deciphering the Function of New Gonococcal Vaccine Antigens Using Phenotypic Microarrays

The function and extracellular location of cell envelope proteins make them attractive candidates for developing vaccines against bacterial diseases, including challenging drug-resistant pathogens, such as Neisseria gonorrhoeae A proteomics-driven reverse vaccinology approach has delivered multiple gonorrhea vaccine candidates; however, the biological functions of many of them remain to be elucidated. Herein, the functions of six gonorrhea vaccine candidates-NGO2121, NGO1985, NGO2054, NGO2111, NGO1205, and NGO1344-in cell envelope homeostasis were probed using phenotype microarrays under 1,056 conditions and a ΔbamE mutant (Δngo1780) as a reference of perturbed outer membrane integrity. Optimal growth conditions for an N. gonorrhoeae phenotype microarray assay in defined liquid medium were developed, which can be useful in other applications, including rapid and thorough antimicrobial susceptibility assessment. Our studies revealed 91 conditions having uniquely positive or negative effects on one of the examined mutants. A cluster analysis of 37 and 57 commonly beneficial and detrimental compounds, respectively, revealed three separate phenotype groups: NGO2121 and NGO1985; NGO1344 and BamE; and the trio of NGO1205, NGO2111, and NGO2054, with the last protein forming an independent branch of this cluster. Similar phenotypes were associated with loss of these vaccine candidates in the highly antibiotic-resistant WHO X strain. Based on their extensive sensitivity phenomes, NGO1985 and NGO2121 appear to be the most promising vaccine candidates. This study establishes the principle that phenotype microarrays can be successfully applied to a fastidious bacterial organism, such as N. gonorrhoeae IMPORTANCE Innovative approaches are required to develop vaccines against prevalent and neglected sexually transmitted infections, such as gonorrhea. Herein, we have utilized phenotype microarrays in the first such investigation into Neisseria gonorrhoeae to probe the function of proteome-derived vaccine candidates in cell envelope homeostasis. Information gained from this screening can feed the vaccine candidate decision tree by providing insights into the roles these proteins play in membrane permeability, integrity, and overall N. gonorrhoeae physiology. The optimized screening protocol can be applied in investigations into the function of other hypothetical proteins of N. gonorrhoeae discovered in the expanding number of whole-genome sequences, in addition to revealing phenotypic differences between clinical and laboratory strains.

Heme Synthesis and Acquisition in Bacterial Pathogens

Bacterial pathogens require the iron-containing cofactor heme to cause disease. Heme is essential to the function of hemoproteins, which are involved in energy generation by the electron transport chain, detoxification of host immune effectors, and other processes. During infection, bacterial pathogens must synthesize heme or acquire heme from the host; however, host heme is sequestered in high-affinity hemoproteins. Pathogens have evolved elaborate strategies to acquire heme from host sources, particularly hemoglobin, and both heme acquisition and synthesis are important for pathogenesis. Paradoxically, excess heme is toxic to bacteria and pathogens must rely on heme detoxification strategies. Heme is a key nutrient in the struggle for survival between host and pathogen, and its study has offered significant insight into the molecular mechanisms of bacterial pathogenesis.

How the Knowledge of Interactions between Meningococcus and the Human Immune System Has Been Used to Prepare Effective Neisseria meningitidis Vaccines

In the last decades, tremendous advancement in dissecting the mechanisms of pathogenicity of Neisseria meningitidis at a molecular level has been achieved, exploiting converging approaches of different disciplines, ranging from pathology to microbiology, immunology, and omics sciences (such as genomics and proteomics). Here, we review the molecular biology of the infectious agent and, in particular, its interactions with the immune system, focusing on both the innate and the adaptive responses. Meningococci exploit different mechanisms and complex machineries in order to subvert the immune system and to avoid being killed. Capsular polysaccharide and lipooligosaccharide glycan composition, in particular, play a major role in circumventing immune response. The understanding of these mechanisms has opened new horizons in the field of vaccinology. Nowadays different licensed meningococcal vaccines are available and used: conjugate meningococcal C vaccines, tetravalent conjugate vaccines, an affordable conjugate vaccine against the N. menigitidis serogroup A, and universal vaccines based on multiple antigens each one with a different and peculiar function against meningococcal group B strains.

Fratricide activity of MafB protein of N. meningitidis strain B16B6

BACKGROUND

Neisseria meningitidis is an inhabitant of the mucosal surfaces of the human nasopharynx. We recently demonstrated that the secreted meningococcal Two-partner secretion protein A (TpsA) is involved in interbacterial competition. The C-terminal end of the large TpsA protein contains a small toxic domain that inhibits the growth of target bacteria. The producing cells are protected from this toxic activity by a small immunity protein that is encoded by the gene immediately downstream of the tpsA gene. Further downstream on the chromosome, a repertoire of toxic modules, designated tpsC cassettes, is encoded that could replace the toxic module of TpsA by recombination. Each tpsC cassette is associated with a gene encoding a cognate immunity protein.

RESULTS

Blast searchers using the toxic domains of TpsA and TpsC proteins as queries identified homologies with the C-terminal part of neisserial MafB proteins, which, for the rest, showed no sequence similarity to TpsA proteins. On the chromosome, mafB genes are part of genomic islands, which include cassettes for additional toxic modules as well as genes putatively encoding immunity proteins. We demonstrate that a MafB protein of strain B16B6 inhibits the growth of a strain that does not produce the corresponding immunity protein. Assays in E. coli confirmed that the C-terminal region of MafB is responsible for toxicity, which is inhibited by the cognate immunity protein. Pull-down assays revealed direct interaction between MafB toxic domains and the cognate immunity proteins.

CONCLUSIONS

The meningococcal MafB proteins are novel toxic proteins involved in interbacterial competition.

Assembly of lipopolysaccharide in Escherichia coli requires the essential LapB heat shock protein

Here, we describe two new heat shock proteins involved in the assembly of LPS in Escherichia coli, LapA and LapB (lipopolysaccharide assembly protein A and B). lapB mutants were identified based on an increased envelope stress response. Envelope stress-responsive pathways control key steps in LPS biogenesis and respond to defects in the LPS assembly. Accordingly, the LPS content in ΔlapB or Δ(lapA lapB) mutants was elevated, with an enrichment of LPS derivatives with truncations in the core region, some of which were pentaacylated and exhibited carbon chain polymorphism. Further, the levels of LpxC, the enzyme that catalyzes the first committed step of lipid A synthesis, were highly elevated in the Δ(lapA lapB) mutant. Δ(lapA lapB) mutant accumulated extragenic suppressors that mapped either to lpxC, waaC, and gmhA, or to the waaQ operon (LPS biosynthesis) and lpp (Braun's lipoprotein). Increased synthesis of either FabZ (3-R-hydroxymyristoyl acyl carrier protein dehydratase), slrA (novel RpoE-regulated non-coding sRNA), lipoprotein YceK, toxin HicA, or MurA (UDP-N-acetylglucosamine 1-carboxyvinyltransferase) suppressed some of the Δ(lapA lapB) defects. LapB contains six tetratricopeptide repeats and, at the C-terminal end, a rubredoxin-like domain that was found to be essential for its activity. In pull-down experiments, LapA and LapB co-purified with LPS, Lpt proteins, FtsH (protease), DnaK, and DnaJ (chaperones). A specific interaction was also observed between WaaC and LapB. Our data suggest that LapB coordinates assembly of proteins involved in LPS synthesis at the plasma membrane and regulates turnover of LpxC, thereby ensuring balanced biosynthesis of LPS and phospholipids consistent with its essentiality.