Cloning of a Neisseria meningitidis gene for L-lactate dehydrogenase (L-LDH): evidence for a second meningococcal L-LDH with different regulation

Two NAD-independent l-lactate dehydrogenases drive l-lactate utilization in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa often establishes a chronic infection in the airways of patients with cystic fibrosis (CF). l-Lactate is the most abundant carbon source in the CF sputum, and l-lactate utilization may be important for P. aeruginosa to survive in the lungs of CF patients. In this study, the key enzymes involved in l-lactate utilization by P. aeruginosa PAO1 were characterized using the synthetic CF sputum medium (SCFM). A highly conserved membrane-bound NAD-independent l-lactate dehydrogenase (l-iLDH) encoded by lldD (PA4771) and a novel flavin-containing membrane-bound l-iLDH encoded by lldA (PA2382) were both found to contribute to l-lactate utilization by P. aeruginosa PAO1. In addition, an lldD and lldA double mutant was incapable of growing in a medium containing l-lactate as the sole carbon source. This study clarifies the mechanism and importance of l-lactate catabolism, and demonstrates the first Pseudomonas spp. expressing two l-lactate-oxidizing enzymes.

Host cell-derived lactate functions as an effector molecule in Neisseria meningitidis microcolony dispersal

The development of meningococcal disease, caused by the human pathogen Neisseria meningitidis, is preceded by the colonization of the epithelial layer in the nasopharynx. After initial adhesion to host cells meningococci form aggregates, through pilus-pilus interactions, termed microcolonies from which the bacteria later detach. Dispersal from microcolonies enables access to new colonization sites and facilitates the crossing of the cell barrier; however, this process is poorly understood. In this study, we used live-cell imaging to investigate the process of N. meningitidis microcolony dispersal. We show that direct contact with host cells is not required for microcolony dispersal, instead accumulation of a host-derived effector molecule induces microcolony dispersal. By using a host-cell free approach, we demonstrated that lactate, secreted from host cells, initiate rapid dispersal of microcolonies. Interestingly, metabolic utilization of lactate by the bacteria was not required for induction of dispersal, suggesting that lactate plays a role as a signaling molecule. Furthermore, Neisseria gonorrhoeae microcolony dispersal could also be induced by lactate. These findings reveal a role of host-secreted lactate in microcolony dispersal and virulence of pathogenic Neisseria.

The human restricted pathogen Neisseria meningitidis is a major cause of bacterial meningitis and sepsis worldwide. Colonization of the mucosal layer in the upper respiratory tract is essential to establish invasive disease. The initial interaction with host cells is characterized by bacterial proliferation and adhesion as aggregates, called microcolonies. Detachment from microcolonies in the nasopharyngeal epithelium facilitates crossing of the cell barrier that can result in invasive disease, yet this process is poorly understood. Here we demonstrate that lactate, an abundant molecule in host mucosal environments, induces N. meningitidis microcolony dispersal. Interestingly, metabolic utilization of lactate by the bacteria was not required for the process, suggesting that lactate play a role as a signaling molecule in pathogenic Neisseria. We propose that the microcolony dispersal in pathogenic Neisseria is influenced by environmental concentrations of lactate. These findings will assist in better understanding the transition from asymptomatic carriage to invasive disease.

Neisseria meningitidis: biology, microbiology, and epidemiology

Neisseria meningitidis (the meningococcus) causes significant morbidity and mortality in children and young adults worldwide through epidemic or sporadic meningitis and/or septicemia. In this review, we describe the biology, microbiology, and epidemiology of this exclusive human pathogen. N.meningitidis is a fastidious, encapsulated, aerobic gram-negative diplococcus. Colonies are positive by the oxidase test and most strains utilize maltose. The phenotypic classification of meningococci, based on structural differences in capsular polysaccharide, lipooligosaccharide (LOS) and outer membrane proteins, is now complemented by genome sequence typing (ST). The epidemiological profile of N. meningitidis is variable in different populations and over time and virulence of the meningococcus is based on a transformable/plastic genome and expression of certain capsular polysaccharides (serogroups A, B, C, W-135, Y and X) and non-capsular antigens. N. meningitidis colonizes mucosal surfaces using a multifactorial process involving pili, twitching motility, LOS, opacity associated, and other surface proteins. Certain clonal groups have an increased capacity to gain access to the blood, evade innate immune responses, multiply, and cause systemic disease. Although new vaccines hold great promise, meningococcal infection continues to be reported in both developed and developing countries, where universal vaccine coverage is absent and antibiotic resistance increasingly more common.

A widely conserved gene cluster required for lactate utilization in Bacillus subtilis and its involvement in biofilm formation

We report that catabolism of l-lactate in Bacillus subtilis depends on the previously uncharacterized yvfV-yvfW-yvbY (herein renamed lutABC) operon, which is inferred to encode three iron-sulfur-containing proteins. The operon is under the dual control of a GntR-type repressor (LutR, formerly YvfI) and the master regulator for biofilm formation SinR and is induced during growth in response to l-lactate. Operons with high similarity to lutABC are present in the genomes of a variety of gram-positive and gram-negative bacteria, raising the possibility that LutABC is a widely conserved and previously unrecognized pathway for the utilization of l-lactate or related metabolites.

Genomic reconstruction of Shewanella oneidensis MR-1 metabolism reveals a previously uncharacterized machinery for lactate utilization

The ability to use lactate as a sole source of carbon and energy is one of the key metabolic signatures of Shewanellae, a diverse group of dissimilatory metal-reducing bacteria commonly found in aquatic and sedimentary environments. Nonetheless, homology searches failed to recognize orthologs of previously described bacterial d- or l-lactate oxidizing enzymes (Escherichia coli genes dld and lldD) in any of the 13 analyzed genomes of Shewanella spp. By using comparative genomic techniques, we identified a conserved chromosomal gene cluster in Shewanella oneidensis MR-1 (locus tag: SO_1522-SO_1518) containing lactate permease and candidate genes for both d- and l-lactate dehydrogenase enzymes. The predicted d-LDH gene (dld-II, SO_1521) is a distant homolog of FAD-dependent lactate dehydrogenase from yeast, whereas the predicted l-LDH is encoded by 3 genes with previously unknown functions (lldEGF, SO_1520-SO_1518). Through a combination of genetic and biochemical techniques, we experimentally confirmed the predicted physiological role of these novel genes in S. oneidensis MR-1 and carried out successful functional validation studies in Escherichia coli and Bacillus subtilis. We conclusively showed that dld-II and lldEFG encode fully functional d-and l-LDH enzymes, which catalyze the oxidation of the respective lactate stereoisomers to pyruvate. Notably, the S. oneidensis MR-1 LldEFG enzyme is a previously uncharacterized example of a multisubunit lactate oxidase. Comparative analysis of >400 bacterial species revealed the presence of LldEFG and Dld-II in a broad range of diverse species accentuating the potential importance of these previously unknown proteins in microbial metabolism.

Modeling Neisseria meningitidis metabolism: from genome to metabolic fluxes

A genome-scale flux model for primary metabolism of Neisseria meningitidis was constructed; a minimal medium for growth of N. meningitidis was designed using the model and tested successfully in batch and chemostat cultures.

Background

Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. In general, most of the recent work on N. meningitidis focuses on potential antigens and their functions, immunogenicity, and pathogenicity mechanisms. Very little work has been carried out on Neisseria primary metabolism over the past 25 years.

Results

Using the genomic database of N. meningitidis serogroup B together with biochemical and physiological information in the literature we constructed a genome-scale flux model for the primary metabolism of N. meningitidis. The validity of a simplified metabolic network derived from the genome-scale metabolic network was checked using flux-balance analysis in chemostat cultures. Several useful predictions were obtained from in silico experiments, including substrate preference. A minimal medium for growth of N. meningitidis was designed and tested succesfully in batch and chemostat cultures.

Conclusion

The verified metabolic model describes the primary metabolism of N. meningitidis in a chemostat in steady state. The genome-scale model is valuable because it offers a framework to study N. meningitidis metabolism as a whole, or certain aspects of it, and it can also be used for the purpose of vaccine process development (for example, the design of growth media). The flux distribution of the main metabolic pathways (that is, the pentose phosphate pathway and the Entner-Douderoff pathway) indicates that the major part of pyruvate (69%) is synthesized through the ED-cleavage, a finding that is in good agreement with literature.

Lactate acquisition promotes successful colonization of the murine genital tract by Neisseria gonorrhoeae

Previous studies on Neisseria gonorrhoeae have demonstrated that metabolism of lactate in the presence of glucose increases the growth rate of the bacterium and enhances its resistance to complement-mediated killing. Although these findings in vitro suggest that the acquisition of lactate promotes gonococcal colonization, the significance of this carbon source to the survival of the gonococcus in vivo remains unknown. To investigate the importance of lactate utilization during Neisseria gonorrhoeae genital tract infection, we identified the gene lctP, which encodes the gonococcal lactate permease. A mutant that lacks a functional copy of lctP was unable to take up exogenous lactate and did not grow in defined medium with lactate as the sole carbon source, in contrast to the wild-type and complemented strains; the mutant strain exhibited no growth defect in defined medium containing glucose. In defined medium containing physiological concentrations of lactate and glucose, the lctP mutant demonstrated reduced early growth and increased sensitivity to complement-mediated killing compared with the wild-type strain; the enhanced susceptibility to complement was associated with a reduction in lipopolysaccharide sialylation of the lctP mutant. The importance of lactate utilization during colonization was evaluated in the murine model of lower genital tract infection. The lctP mutant was significantly attenuated in its ability to colonize and survive in the genital tract, while the complemented mutant exhibited no defect for colonization. Lactate is a micronutrient in the genital tract that contributes to the survival of the gonococcus.

Available carbon source influences the resistance of Neisseria meningitidis against complement

Neisseria meningitidis is an important cause of septicaemia and meningitis. To cause disease, the bacterium must acquire essential nutrients for replication in the systemic circulation, while avoiding exclusion by host innate immunity. Here we show that the utilization of carbon sources by N. meningitidis determines its ability to withstand complement-mediated lysis, through the intimate relationship between metabolism and virulence in the bacterium. The gene encoding the lactate permease, lctP, was identified and disrupted. The lctP mutant had a reduced growth rate in cerebrospinal fluid compared with the wild type, and was attenuated during bloodstream infection through loss of resistance against complement-mediated killing. The link between lactate and complement was demonstrated by the restoration of virulence of the lctP mutant in complement (C3(-/-))-deficient animals. The underlying mechanism for attenuation is mediated through the sialic acid biosynthesis pathway, which is directly connected to central carbon metabolism. The findings highlight the intimate relationship between bacterial physiology and resistance to innate immune killing in the meningococcus.

Genomic-scale analysis of Pasteurella multocida gene expression during growth within liver tissue of chickens with fowl cholera

We have recently reported the gene expression profile of Pasteurella multocida during growth in the blood of chickens with fowl cholera. Here we report the gene expression profile of P. multocida during growth in the livers of similarly infected chickens. We compared expression profiles of bacteria harvested from the livers of infected chickens with late-stage fowl cholera with those of bacteria grown in rich medium. Independent analysis of bacterial expression profiles from three individual chickens indicated that 93 P. multocida genes were always differentially expressed during growth in liver tissue. Of these 93 genes, 49 were upregulated and 44 downregulated in the host. Many of the upregulated genes were involved in energy production and conversion (9/49) and carbohydrate transport and metabolism (8/49), and a number of these have been shown to be induced under anaerobic conditions in other species. The downregulated genes were generally of unknown or poorly characterised functions (14/44). Comparison of the differentially regulated gene sets identified for growth in liver with those identified previously for growth in blood allowed the identification of a core set of 13 upregulated and 16 downregulated genes that were differentially regulated in at least five of the six infections studied.

Comparative whole-genome analyses reveal over 100 putative phase-variable genes in the pathogenic Neisseria spp

Previously, a complete genome analysis of Neisseria meningitidis strain MC58 revealed the largest repertoire of putative phase-variable genes described in any species to date. Initial comparisons with two incomplete Neisseria spp. genome sequences available at that time revealed differences in the repeats associated with these genes in the form of polymorphisms, the absence of the potentially unstable elements in some alleles, and in the repertoire of the genes that were present. Analyses of the complete genomes of N. meningitidis strain Z2491 and Neisseria gonorrhoeae strain FA1090 have been performed and are combined with a comprehensive comparative analysis between the three available complete genome sequences. This has increased the sensitivity of these searches and provided additional contextual information that facilitates the interpretation of the functional consequences of repeat instability. This analysis identified: (i) 68 phase-variable gene candidates in N. meningitidis strain Z2491, rather than the 27 previously reported; (ii) 83 candidates in N. gonorrhoeae strain FA1090; and (iii) 82 candidates in N. meningitidis strain MC58, including an additional 19 identified through cross-comparisons with the other two strains. In addition to the 18 members of the opa gene family, a repertoire of 119 putative phase-variable genes is described, indicating a huge potential for diversification mediated by this mechanism of gene switching in these species that is central to their interactions with the host and environmental transitions. Eighty-two of these are either known (14) or strong (68) candidates for phase variation, which together with the opa genes make a total of 100 identified genes. The repertoires of the genes identified in this analysis diverge from the different species groupings, indicating horizontal exchange that significantly affects the species and strain complements of these genes.

An NMR and enzyme study of the carbon metabolism of Neisseria meningitidis

The pathogenic neisseriae are fastidious bacteria that are only able to grow on a restricted range of carbon sources. The genome sequence of Neisseria meningitidis strain MC58 predicts the presence of a complete citric acid cycle (CAC), but there have been no detailed biochemical studies of carbon metabolism in this important pathogen. In this study, both NMR and conventional enzyme assays were used to investigate the central metabolic pathways of a serogroup B strain (K454). (13)C-NMR labelling patterns of amino acids from hydrolysed cell proteins after growth with either 2- or 3-[(13)C]pyruvate were consistent with the operation of a complete oxidative CAC. Enzyme assays showed that cell-free extracts contained all the CAC enzymes predicted from the genome sequence, including a membrane-bound malate:quinone oxidoreductase which is present in place of the conventional NAD-linked cytoplasmic malate dehydrogenase. (1)H-NMR studies showed that growth on glucose, lactate and, especially, pyruvate, resulted in the excretion of significant amounts of acetate into the culture supernatant. This occurred via the phosphotransacetylase (PTA)-acetate kinase (ACK) pathway. Extremely high specific activities of PTA (7-14 micromol min(-1) mg(-1)) were detected in cell-free extracts, although ACK activities were much lower (46-298 nmol min(-1) mg(-1)). Expression of PTA and ACK activities was not co-ordinately regulated during growth on combinations of carbon sources. This may be related to the presence of two ackA paralogues in N. meningitidis which are, unusually, unlinked to the pta gene.

In a medium containing glucose, lactate carbon is incorporated by gonococci predominantly into fatty acids and glucose carbon incorporation is increased: implications regarding lactate stimulation of metabolism

The reason for stimulation by lactate of metabolism of gonococci growing in a medium containing glucose, which enhances pathogenicity by increasing growth rate, lipopolysaccharide (LPS) synthesis and protein formation, has been investigated. Tricine dodecylpolyacrylamide gel electrophoresis (SDS-PAGE) and thin layer chromatography (TLC) on homogenates of gonococci grown in this medium with [14C]lactate showed that lactate carbon was preferentially incorporated into lipid and LPS. Nuclear magnetic resonance (NMR) spectroscopy on lipid extracted from gonococci grown in the glucose containing medium with [13C]lactate showed that lactate carbon was incorporated into fatty acid moieties and not into ethanolamine or glycerol moieties. In contrast, NMR on lipid from gonococci grown with [13C]glucose indicated glucose carbon in both moieties. When unlabelled lactate was added, lipid synthesis from [l3C]glucose was stimulated and small amounts of different fatty acids were formed. The NMR data shows that gluconeogenesis from lactate carbon does not occur in the presence of glucose, suggesting that lactate is used solely for rapid production, via pyruvate, of acetyl CoA, the precursor not only for fatty acid synthesis but also for the constituents and products of the citric acid cycle, including ATP. The rapid formation of a high level of acetyl CoA is the probable reason for the stimulation of metabolism and oxygen uptake by lactate. 14C label on LPS was detected in its fatty acids. Most proteins that stained with silver in tricine SDS-PAGE were not significantly labelled by [14C]lactate in the glucose-containing medium. Two of three appreciably labelled proteins were identified by N-terminal sequencing as GroEL and porin 1B, and one of the two less labelled proteins was similar to peroxiredoxin type proteins. There were no signs of specific induction of these proteins by lactate and their labelling was consistent with fatty acids in attached lipid.

Natural genetic exchange between Haemophilus and Neisseria: intergeneric transfer of chromosomal genes between major human pathogens

Members of the bacterial families Haemophilus and Neisseria, important human pathogens that commonly colonize the nasopharynx, are naturally competent for DNA uptake from their environment. In each genus this process is discriminant in favor of its own and against foreign DNA through sequence specificity of DNA receptors. The Haemophilus DNA uptake apparatus binds a 29-bp oligonucleotide domain containing a highly conserved 9-bp core sequence, whereas the neisserial apparatus binds a 10-bp motif. Each motif ("uptake sequence", US) is highly over-represented in the chromosome of the corresponding genus, particularly concentrated with core sequences in inverted pairs forming gene terminators. Two Haemophilus core USs were unexpectedly found forming the terminator of sodC in Neisseria meningitidis (meningococcus), and sequence analysis strongly suggests that this virulence gene, located next to IS1106, arose through horizontal transfer from Haemophilus. By using USs as search strings in a computer-based analysis of genome sequence, it was established that while USs of the "wrong" genus do not occur commonly in Neisseria or Haemophilus, where they do they are highly likely to flag domains of chromosomal DNA that have been transferred from Haemophilus. Three independent domains of Haemophilus-like DNA were found in the meningococcal chromosome, associated respectively with the virulence gene sodC, the bio gene cluster, and an unidentified orf. This report identifies intergenerically transferred DNA and its source in bacteria, and further identifies transformation with heterologous chromosomal DNA as a way of establishing potentially important chromosomal mosaicism in these pathogenic bacteria.

Conservation of the lipooligosaccharide synthesis locus lgt among strains of Neisseria gonorrhoeae: requirement for lgtE in synthesis of the 2C7 epitope and of the beta chain of strain 15253

The present study was undertaken to examine the extent to which the lgt locus varies among strains of gonococci. This locus encodes five glycosyl transferases involved in the synthesis of the lipooligosaccharide (LOS) of Neisseria gonorrhoeae. We examined seven gonococcal strains and found that the structure of the lgt locus is conserved among six of these strains. The locus is strikingly altered in strain 15253. This is one of the few strains where extensive structural analysis of its LOS is available, and therefore, we defined the altered lgt locus and focused on the reactivity of mAB 2C7. We found that strain 15253 contains only two lgt genes, lgtA and lgtE. As in F62, lgtA encodes a GlcNAc transferase and is subject to phase variation. In addition, by analysis of deletion mutants, we found that lgtE, which encodes a galactosyl transferase that is required for elongating the alpha-chain, is also necessary for completing the beta chain.