In this review we address the subject of dental caries pathogenicity from a genomic and metagenomic perspective. The application of genomic technologies is certain to yield novel insights into the relationship between the bacterial flora, dental health and disease. Three primary attributes of bacterial species are thought to have direct impact on caries development, these include: adherence on tooth surfaces (biofilm formation), acid production and acid tolerance. Attempts to define the specific aetiological agents of dental caries have proven to be elusive, supporting the notion that caries aetiology is perhaps complex and multi-faceted. The recently introduced Human Microbiome Project (HMP) that endeavors to characterise the micro-organisms living in and on the human body is likely to shed new light on these questions and improve our understanding of polymicrobial disease, microbial ecology in the oral cavity and provide new avenues for therapeutic and molecular diagnostics developments.
Caries; biofilm; bacterial species; genomic; metagenomic; Human Microbiome Project
In bacterial two-component regulatory systems (TCSs), dephosphorylation of phosphorylated response regulators is essential for resetting the activated systems to the pre-activation state. However, in the SaeRS TCS, a major virulence TCS of Staphylococcus aureus, the mechanism for dephosphorylation of the response regulator SaeR has not been identified. Here we report that two auxiliary proteins from the sae operon, SaeP and SaeQ, form a protein complex with the sensor kinase SaeS and activate the sensor kinase’s phosphatase activity. Efficient activation of the phosphatase activity required the presence of both SaeP and SaeQ. When SaeP and SaeQ were ectopically expressed, the expression of coagulase, a sae target with low affinity for phosphorylated SaeR, was greatly reduced, while the expression of alpha-hemolysin, a sae target with high affinity for phosphorylated SaeR, was not, demonstrating a differential effect of SaePQ on sae target gene expression. When expression of SaePQ was abolished, most sae target genes were induced at an elevated level. Since the expression of SaeP and SaeQ is induced by the SaeRS TCS, these results suggest that the SaeRS TCS returns to the pre-activation state by a negative feedback mechanism.
Bacteria; Membrane proteins; Lipoproteins; Negative-feedback; Phosphatase
Pan-aminoglycoside-resistant Pseudomonas aeruginosa mutants expressing the mexXY components of the aminoglycoside-accommodating MexXY-OprM multidrug efflux system but lacking mutations in the mexZ gene encoding a repressor of this efflux system and in the mexXY promoter have been reported (S. Fraud and K. Poole, Antimicrob. Agents Chemother. 55:1068–1074, 2011). Genome sequencing of one of these mutants, K2966, revealed the presence of a mutation within the predicted promoter region of the rplU-rpmA operon encoding ribosomal proteins L21 and L27, consistent with an observed 2-fold decrease in expression of this operon in the mutant relative to wild-type P. aeruginosa PAO1. Moreover, correction of the mutation restored rplU-rpmA expression and, significantly, reversed the elevated mexXY expression and pan-aminoglycoside resistance of the mutant. Reduced rplU-rpmA expression was also observed in a second mexXY-expressing pan-aminoglycoside-resistant mutant, K2968, which, however, lacked a mutation in the rplU-rpmA promoter region. Restoration of rplU-rpmA expression in the K2968 mutant following chromosomal integration of the rplU-rpmA operon derived from wild-type P. aeruginosa failed, however, to reverse the elevated mexXY expression and pan-aminoglycoside resistance of this mutant, although it did so for K2966, suggesting that the mutation impacting rplU-rpmA expression in K2968 also impacts other mexXY-related genes. Increased mexXY expression owing to reduced rplU-rpmA expression in K2966 and K2968 was dependent on PA5471, whose expression was also elevated in these mutants. Thus, mutational disruption of ribosome function, by limiting expression of ribosomal constituents, promotes recruitment of mexXY and does so via PA5471, reminiscent of mexXY induction by ribosome-disrupting antimicrobial agents. Interestingly, reduced rplU-rpmA expression was also observed in a mexXY-expressing pan-aminoglycoside-resistant clinical isolate, suggesting that ribosome-perturbing mutations have clinical relevance in the recruitment of the MexXY-OprM aminoglycoside resistance determinant.
Dental decay is one of the most prevalent chronic diseases worldwide. A variety of factors, including microbial, genetic, immunological, behavioral and environmental, interact to contribute to dental caries onset and development. Previous studies focused on the microbial basis for dental caries have identified species associated with both dental health and disease. The purpose of the current study was to improve our knowledge of the microbial species involved in dental caries and health by performing a comprehensive 16S rDNA profiling of the dental plaque microbiome of both caries-free and caries-active subjects. Analysis of over 50,000 nearly full-length 16S rDNA clones allowed the identification of 1,372 operational taxonomic units (OTUs) in the dental plaque microbiome. Approximately half of the OTUs were common to both caries-free and caries-active microbiomes and present at similar abundance. The majority of differences in OTU’s reflected very low abundance phylotypes. This survey allowed us to define the population structure of the dental plaque microbiome and to identify the microbial signatures associated with dental health and disease. The deep profiling of dental plaque allowed the identification of 87 phylotypes that are over-represented in either caries-free or caries-active subjects. Among these signatures, those associated with dental health outnumbered those associated with dental caries by nearly two-fold. A comparison of this data to other published studies indicate significant heterogeneity in study outcomes and suggest that novel approaches may be required to further define the signatures of dental caries onset and progression.
Oxygen sensing and redox signaling significantly affect bacterial physiology and host-pathogen interaction. Here we show that a Staphylococcus aureus two-component system, AirSR (anaerobic iron-sulfur cluster-containing redox sensor regulator, formerly YhcSR), responds to oxidation signals (O2, H2O2, NO, etc) by using a redox-active [2Fe-2S] cluster in the sensor kinase AirS. Mutagenesis studies demonstrate that the [2Fe-2S] cluster is essential for the kinase activity of AirS. We have also discovered that a homolog of IscS (SA1450) in S. aureus is active as a cysteine desulfurase, which enables the in vitro reconstitution of the [2Fe-2S] cluster in AirS. Phosphorylation assays show that the oxidized AirS with a [2Fe-2S]2+ cluster is the fully active form of the kinase but not the apo-AirS nor the reduced AirS possessing a [2Fe-2S]+ cluster. Over-oxidation by prolonged exposure to O2 or contact with H2O2 or NO led to inactivation of AirS. Transcriptome analysis revealed that mutation of airR impacts the expression of ~355 genes under anaerobic conditions. Moreover, the mutant strain displayed increased resistance toward H2O2, vancomycin, norfloxacin, and ciprofloxacin under anaerobic conditions. Together, our results show that S. aureus AirSR is a redox-dependent global regulatory system that plays important roles in gene regulation using a redox active Fe-S cluster under O2-limited conditions.
The structural characterization of acyl-carrier-protein synthase (AcpS) from three different pathogenic microorganisms is reported. One interesting finding of the present work is a crystal artifact related to the activity of the enzyme, which fortuitously represents an opportunity for a strategy to design a potential inhibitor of a pathogenic AcpS.
Some bacterial type II fatty-acid synthesis (FAS II) enzymes have been shown to be important candidates for drug discovery. The scientific and medical quest for new FAS II protein targets continues to stimulate research in this field. One of the possible additional candidates is the acyl-carrier-protein synthase (AcpS) enzyme. Its holo form post-translationally modifies the apo form of an acyl carrier protein (ACP), which assures the constant delivery of thioester intermediates to the discrete enzymes of FAS II. At the Center for Structural Genomics of Infectious Diseases (CSGID), AcpSs from Staphylococcus aureus (AcpSSA), Vibrio cholerae (AcpSVC) and Bacillus anthracis (AcpSBA) have been structurally characterized in their apo, holo and product-bound forms, respectively. The structure of AcpSBA is emphasized because of the two 3′,5′-adenosine diphosphate (3′,5′-ADP) product molecules that are found in each of the three coenzyme A (CoA) binding sites of the trimeric protein. One 3′,5′-ADP is bound as the 3′,5′-ADP part of CoA in the known structures of the CoA–AcpS and 3′,5′-ADP–AcpS binary complexes. The position of the second 3′,5′-ADP has never been described before. It is in close proximity to the first 3′,5′-ADP and the ACP-binding site. The coordination of two ADPs in AcpSBA may possibly be exploited for the design of AcpS inhibitors that can block binding of both CoA and ACP.
acyl-carrier-protein synthase; acyl carrier protein; type II fatty-acid synthesis; inhibition; 3′,5′-adenosine diphosphate; coenzyme A
Here we report the use of a multi-genome DNA microarray to investigate the genome diversity of Bacillus cereus group members and elucidate the events associated with the emergence of B. anthracis the causative agent of anthrax–a lethal zoonotic disease. We initially performed directed genome sequencing of seven diverse B. cereus strains to identify novel sequences encoded in those genomes. The novel genes identified, combined with those publicly available, allowed the design of a “species” DNA microarray. Comparative genomic hybridization analyses of 41 strains indicates that substantial heterogeneity exists with respect to the genes comprising functional role categories. While the acquisition of the plasmid-encoded pathogenicity island (pXO1) and capsule genes (pXO2) represent a crucial landmark dictating the emergence of B. anthracis, the evolution of this species and its close relatives was associated with an overall a shift in the fraction of genes devoted to energy metabolism, cellular processes, transport, as well as virulence.
Genome-scale metabolic network reconstruction and analysis of the murine leukemic macrophage cell line RAW 264.7 reveal a complementary relationship between how known metabolic immunomodulators are biochemically processed and their role in macrophage activation.
The RAW 264.7 metabolic model was constructed based on transcriptomic and proteomic data, and validated for its quantitative accuracy in the prediction of growth rate, ATP, and nitric oxide production.Metabolic network-based analyses identified well-established critical metabolite effectors and intracellular pathways that impact activation or suppression of M1- and M2-metabolic activation phenotypes.Three levels of high-throughput data (transcriptomic, proteomic, and metabolomic) were analyzed in the context of the model-based predictions to elucidate underlying metabolic mechanisms of macrophage activation.Results suggest a potential contending link between de-novo nucleotide synthesis and macrophage activation phenotypes at a glutamine junction.
Macrophages are central players in immune response, manifesting divergent phenotypes to control inflammation and innate immunity through release of cytokines and other signaling factors. Recently, the focus on metabolism has been reemphasized as critical signaling and regulatory pathways of human pathophysiology, ranging from cancer to aging, often converge on metabolic responses. Here, we used genome-scale modeling and multi-omics (transcriptomics, proteomics, and metabolomics) analysis to assess metabolic features that are critical for macrophage activation. We constructed a genome-scale metabolic network for the RAW 264.7 cell line to determine metabolic modulators of activation. Metabolites well-known to be associated with immunoactivation (glucose and arginine) and immunosuppression (tryptophan and vitamin D3) were among the most critical effectors. Intracellular metabolic mechanisms were assessed, identifying a suppressive role for de-novo nucleotide synthesis. Finally, underlying metabolic mechanisms of macrophage activation are identified by analyzing multi-omic data obtained from LPS-stimulated RAW cells in the context of our flux-based predictions. Our study demonstrates metabolism's role in regulating activation may be greater than previously anticipated and elucidates underlying connections between activation and metabolic effectors.
constraint-based modeling; immunometabolism; metabolic network reconstruction; RAW 264.7
What is the minimum number of genes or functions necessary to support cellular life? The concept of a 'minimal genome' has become popular, but is it a useful concept, and if so, what might a minimal genome encode? We argue that the concept may be useful, even though the goal of defining a general minimal genome may never be attained.
The pathogenic mold Aspergillus fumigatus is the most frequent infectious cause of death in severely immunocompromised individuals such as leukemia and bone marrow transplant patients. Germination of inhaled conidia (asexual spores) in the host is critical for the initiation of infection, but little is known about the underlying mechanisms of this process.
To gain insights into early germination events and facilitate the identification of potential stage-specific biomarkers and vaccine candidates, we have used quantitative shotgun proteomics to elucidate patterns of protein abundance changes during early fungal development. Four different stages were examined: dormant conidia, isotropically expanding conidia, hyphae in which germ tube emergence has just begun, and pre-septation hyphae. To enrich for glycan-linked cell wall proteins we used an alkaline cell extraction method. Shotgun proteomic resulted in the identification of 375 unique gene products with high confidence, with no evidence for enrichment of cell wall-immobilized and secreted proteins. The most interesting discovery was the identification of 52 proteins enriched in dormant conidia including 28 proteins that have never been detected in the A. fumigatus conidial proteome such as signaling protein Pil1, chaperones BipA and calnexin, and transcription factor HapB. Additionally we found many small, Aspergillus specific proteins of unknown function including 17 hypothetical proteins. Thus, the most abundant protein, Grg1 (AFUA_5G14210), was also one of the smallest proteins detected in this study (M.W. 7,367). Among previously characterized proteins were melanin pigment and pseurotin A biosynthesis enzymes, histones H3 and H4.1, and other proteins involved in conidiation and response to oxidative or hypoxic stress. In contrast, expanding conidia, hyphae with early germ tubes, and pre-septation hyphae samples were enriched for proteins responsible for housekeeping functions, particularly translation, respiratory metabolism, amino acid and carbohydrate biosynthesis, and the tricarboxylic acid cycle.
The observed temporal expression patterns suggest that the A. fumigatus conidia are dominated by small, lineage-specific proteins. Some of them may play key roles in host-pathogen interactions, signal transduction during conidial germination, or survival in hostile environments.
Mass spectrometry; LC-MS/MS; APEX; Shotgun proteomics; Aspergillus fumigatus; Germination; Spore; Conidia; Fungi; Hypothetical proteins
Dehydroquinate dehydratase (DHQD) catalyzes the third step in the biosynthetic shikimate pathway. We present three crystal structures of the Salmonella enterica type I DHQD which address the functionality of a surface loop that is observed to close over the active site following substrate binding. Two wild type structures with differing loop conformations and kinetic and structural studies of a mutant provide evidence of both direct and indirect mechanisms of loop involvement in substrate binding. In addition to allowing amino acid side chains to establish a direct interaction with the substrate, loop closure necessitates a conformational change of a key active site arginine, which in turn positions the substrate productively. The absence of DHQD in humans and its essentiality in many pathogenic bacteria makes the enzyme a target for the development of nontoxic antimicrobials. The structures and ligand binding insights presented here may inform the design of novel type I DHQD inhibiting molecules.
Toll-like receptors (TLRs) contribute to host resistance to microbial pathogens and drive the evolution of virulence mechanisms. We have examined the relationship between host resistance and pathogen virulence using mice with a functional allele of the Nramp-1 gene and lacking combinations of TLRs. Mice deficient in both TLR2 and TLR4 were highly susceptible to the intracellular bacterial pathogen Salmonella typhimurium, consistent with reduced innate immune function. However, mice lacking additional TLRs involved in S. typhimurium recognition were less susceptible to infection. In these TLR-deficient cells, bacteria failed to upregulate Salmonella pathogenicity island 2 (SPI-2) genes and did not form a replicative compartment. We demonstrate that TLR signaling enhances the rate of acidification of the Salmonella containing phagosome, and inhibition of this acidification prevents SPI-2 induction. Our results indicate that S. typhimurium requires cues from the innate immune system to regulate virulence genes necessary for intracellular survival, growth, and systemic infection.
In this work we describe the identification of a copper-inducible regulon in Mycobacterium tuberculosis (Mtb). Among the regulated genes was Rv0190/MT0200, a paralogue of the copper metalloregulatory repressor CsoR. The five-locus regulon, which includes a gene that encodes the copper-protective metallothionein MymT, was highly induced in wild type Mtb treated with copper, and highly expressed in an Rv0190/MT0200 mutant. Importantly, the Rv0190/MT0200 mutant was hyper-resistant to copper. The promoters of all five loci share a palindromic motif that was recognized by the gene product of Rv0190/MT0200. For this reason we named Rv0190/MT0200 RicR for regulated in copper repressor. Intriguingly, several of the RicR-regulated genes, including MymT, are unique to pathogenic Mycobacteria. The identification of a copper-responsive regulon specific to virulent mycobacterial species suggests copper homeostasis must be maintained during an infection. Alternatively, copper may provide a cue for the expression of genes unrelated to metal homeostasis, but nonetheless necessary for survival in a host.
Here we report the use of a multi-genome DNA microarray to elucidate the genomic events associated with the emergence of the clonal variants of H. influenzae biogroup aegyptius causing Brazilian Purpuric Fever (BPF), an important pediatric disease with a high mortality rate. We performed directed genome sequencing of strain HK1212 unique loci to construct a species DNA microarray. Comparative genome hybridization using this microarray enabled us to determine and compare gene complements, and infer reliable phylogenomic relationships among members of the species. The higher genomic variability observed in the genomes of BPF-related strains (clones) and their close relatives may be characterized by significant gene flux related to a subset of functional role categories. We found that the acquisition of a large number of virulence determinants featuring numerous cell membrane proteins coupled to the loss of genes involved in transport, central biosynthetic pathways and in particular, energy production pathways to be characteristics of the BPF genomic variants.
Haemophilus; Brazilian Purpuric Fever; pathogen emergence; virulence; comparative genomics; microarray
We describe here a clinical daptomycin treatment failure in a patient with recurrent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia in whom daptomycin was administered after a failed empirical treatment course with vancomycin and piperacillin-tazobactam. We had the opportunity to compare the genome sequences of an isogenic pair of daptomycin-susceptible and -resistant MRSA isolates obtained before and after initiation of daptomycin therapy, respectively. The genotype of both isolates was USA800, ST5, SCCmec type IV, agr type II. There was no increase in cell wall thickness in the daptomycin-resistant strain despite having decreased susceptibility to both vancomycin and daptomycin. By comparing the genome sequences by pyrosequencing, we identified a polymorphism (S337L) in the tenth transmembrane segment of the multiple peptide resistance factor, MprF, encoding lysyl phosphatidylglycerol transferase. This enzyme has been shown previously to promote repulsion of daptomycin at the cell surface by addition of positively charged lysine to phosphatidylglycerol. Also, the hlb open reading frame (ORF) encoding the β-toxin was interrupted by a prophage in the daptomycin-susceptible strain; this phage was missing in the daptomycin-resistant isolate and the hlb ORF was restored. Loss of the phage in the resistant isolate also resulted in loss of the virulence factor genes clpP, scn, and sak. This is the first study to use pyrosequencing to compare the genomes of a daptomycin-susceptible/resistant MRSA isolate pair obtained during failed daptomycin therapy in humans.
Shigella dysenteriae serotype 1 (SD1) causes the most severe form of epidemic bacillary dysentery. Quantitative proteome profiling of Shigella dysenteriae serotype 1 (SD1) in vitro (derived from LB cell cultures) and in vivo (derived from gnotobiotic piglets) was performed by 2D-LC-MS/MS and APEX, a label-free computationally modified spectral counting methodology.
Overall, 1761 proteins were quantitated at a 5% FDR (false discovery rate), including 1480 and 1505 from in vitro and in vivo samples, respectively. Identification of 350 cytoplasmic membrane and outer membrane (OM) proteins (38% of in silico predicted SD1 membrane proteome) contributed to the most extensive survey of the Shigella membrane proteome reported so far. Differential protein abundance analysis using statistical tests revealed that SD1 cells switched to an anaerobic energy metabolism under in vivo conditions, resulting in an increase in fermentative, propanoate, butanoate and nitrate metabolism. Abundance increases of transcription activators FNR and Nar supported the notion of a switch from aerobic to anaerobic respiration in the host gut environment. High in vivo abundances of proteins involved in acid resistance (GadB, AdiA) and mixed acid fermentation (PflA/PflB) indicated bacterial survival responses to acid stress, while increased abundance of oxidative stress proteins (YfiD/YfiF/SodB) implied that defense mechanisms against oxygen radicals were mobilized. Proteins involved in peptidoglycan turnover (MurB) were increased, while β-barrel OM proteins (OmpA), OM lipoproteins (NlpD), chaperones involved in OM protein folding pathways (YraP, NlpB) and lipopolysaccharide biosynthesis (Imp) were decreased, suggesting unexpected modulations of the outer membrane/peptidoglycan layers in vivo. Several virulence proteins of the Mxi-Spa type III secretion system and invasion plasmid antigens (Ipa proteins) required for invasion of colonic epithelial cells, and release of bacteria into the host cell cytosol were increased in vivo.
Global proteomic profiling of SD1 comparing in vivo vs. in vitro proteomes revealed differential expression of proteins geared towards survival of the pathogen in the host gut environment, including increased abundance of proteins involved in anaerobic energy respiration, acid resistance and virulence. The immunogenic OspC2, OspC3 and IpgA virulence proteins were detected solely under in vivo conditions, lending credence to their candidacy as potential vaccine targets.
The Staphylococcus aureus surface protein G (SasG) is an important mediator of biofilm formation in virulent S. aureus strains. A detailed analysis of its primary sequence has not been reported to date. SasG is highly abundant in the cell wall of the vancomycin-intermediate S. aureus strain HIP5827, and was purified and subjected to sequence analysis by MS. Data from MALDI-TOF and LC-MS/MS experiments confirmed the predicted N-terminal signal peptide cleavage site at residue A51 and the C-terminal cell wall anchor site at residue T1086. The protein was also derivatized with N-succinimidyloxycarbonyl-methyl-tris(2,4,6-trimethoxyphenyl) phosphonium bromide (TMPP-Ac-OSu) to assess the presence of additional N-terminal sites of mature SasG. TMPP-derivatized SasG peptides featured m/z peaks with a 572 Da mass increase over the equivalent underivatized peptides. Multiple N-terminal peptides, all of which were observed in the 150 amino acid segment following the signal peptide cleavage at the residue A51, were characterized from MS and MS/MS data, suggesting a series of successive N-terminal truncations of SasG. A strategy combining TMPP derivatization, multiple enzyme digestions to generate overlapping peptides and detailed MS analysis will be useful to determine and understand functional implications of PTMs in bacterial cell wall-anchored proteins, which are frequently involved in the modulation of virulence-associated bacterial surface properties.
N-terminal truncation; TMPP labeling; multiple enzyme digestion; SasG; mass spectrometry; post-translational modifications
Uncharacterized proteases naturally expressed by bacterial pathogens represents important topic in infectious disease research, because these enzymes may have critical roles in pathogenicity and cell physiology. It has been observed that cloning, expression and purification of proteases often fail due to their catalytic functions which, in turn, cause toxicity in the E. coli heterologous host.
In order to address this problem systematically, a modified pipeline of our high-throughput protein expression and purification platform was developed. This included the use of a specific E. coli strain, BL21(DE3) pLysS to tightly control the expression of recombinant proteins and various expression vectors encoding fusion proteins to enhance recombinant protein solubility. Proteases fused to large fusion protein domains, maltosebinding protein (MBP), SP-MBP which contains signal peptide at the N-terminus of MBP, disulfide oxidoreductase (DsbA) and Glutathione S-transferase (GST) improved expression and solubility of proteases. Overall, 86.1% of selected protease genes including hypothetical proteins were expressed and purified using a combination of five different expression vectors. To detect novel proteolytic activities, zymography and fluorescence-based assays were performed and the protease activities of more than 46% of purified proteases and 40% of hypothetical proteins that were predicted to be proteases were confirmed.
Multiple expression vectors, employing distinct fusion tags in a high throughput pipeline increased overall success rates in expression, solubility and purification of proteases. The combinatorial functional analysis of the purified proteases using fluorescence assays and zymography confirmed their function.
While the pneumococcal protein conjugate vaccines reduce the incidence in invasive pneumococcal disease (IPD), serotype replacement remains a major concern. Thus, serotype-independent protection with vaccines targeting virulence genes, such as PspA, have been pursued. PspA is comprised of diverse clades that arose through recombination. Therefore, multi-locus sequence typing (MLST)-defined clones could conceivably include strains from multiple PspA clades. As a result, a method is needed which can both monitor the long-term epidemiology of the pneumococcus among a large number of isolates, and analyze vaccine-candidate genes, such as pspA, for mutations and recombination events that could result in ‘vaccine escape’ strains.
We developed a resequencing array consisting of five conserved and six variable genes to characterize 72 pneumococcal strains. The phylogenetic analysis of the 11 concatenated genes was performed with the MrBayes program, the single nucleotide polymorphism (SNP) analysis with the DNA Sequence Polymorphism program (DnaSP), and the recombination event analysis with the recombination detection package (RDP).
The phylogenetic analysis correlated with MLST, and identified clonal strains with unique PspA clades. The DnaSP analysis correlated with the serotype-specific diversity detected using MLST. Serotypes associated with more than one ST complex had a larger degree of sequence polymorphism than a serotype associated with one ST complex. The RDP analysis confirmed the high frequency of recombination events in the pspA gene.
The phylogenetic tree correlated with MLST, and detected multiple PspA clades among clonal strains. The genetic diversity of the strains and the frequency of recombination events in the mosaic gene, pspA were accurately assessed using the DnaSP and RDP programs, respectively. These data provide proof-of-concept that resequencing arrays could play an important role within research and clinical laboratories in both monitoring the molecular epidemiology of the pneumococcus and detecting ‘vaccine escape’ strains among vaccine-candidate genes.
Shigella dysenteriae serotype 1 (SD1) causes the most severe form of epidemic bacillary dysentery. We present the first comprehensive proteome analysis of this pathogen, profiling proteins from bacteria cultured in vitro and bacterial isolates from the large bowel of infected gnotobiotic piglets (in vivo). Overall, 1061 distinct gene products were identified. Differential display analysis revealed that SD1 cells switched to an anaerobic energy metabolism in vivo. High in vivo abundances of amino acid decarboxylases (GadB and AdiA) which enhance pH homeostasis in the cytoplasm and protein disaggregation chaperones (HdeA, HdeB and ClpB) were indicative of a coordinated bacterial survival response to acid stress. Several type III secretion system (T3SS) effectors were increased in abundance in vivo, including OspF, IpaC and IpaD. These proteins are implicated in invasion of colonocytes and subversion of the host immune response in S. flexneri. These observations likely reflect an adaptive response of SD1 to the hostile host environment. Seven proteins, among them the T3SS effectors OspC2 and IpaB, were detected as antigens in western blots using piglet antisera. The outer membrane protein OmpA, the heat shock protein HtpG and OspC2 represent novel SD1 subunit vaccine candidates and drug targets.
acid stress; bacillary dysentery; proteome analysis; Shigella dysenteriae
Mutations within codon 306 of the Mycobacterium tuberculosis embB gene modestly increase ethambutol (EMB) MICs. To identify other causes of EMB resistance and to identify causes of high-level resistance, we generated EMB-resistant M. tuberculosis isolates in vitro and performed allelic exchange studies of embB codon 406 (embB406) and embB497 mutations. In vitro selection produced mutations already identified clinically in embB306, embB397, embB497, embB1024, and embC13, which result in EMB MICs of 8 or 14 μg/ml, 5 μg/ml, 12 μg/ml, 3 μg/ml, and 4 μg/ml, respectively, and mutations at embB320, embB324, and embB445, which have not been identified in clinical M. tuberculosis isolates and which result in EMB MICs of 8 μg/ml, 8 μg/ml, and 2 to 8 μg/ml, respectively. To definitively identify the effect of the common clinical embB497 and embB406 mutations on EMB susceptibility, we created a series of isogenic mutants, exchanging the wild-type embB497 CAG codon in EMB-susceptible M. tuberculosis strain 210 for the embB497 CGG codon and the wild-type embB406 GGC codon for either the embB406 GCC, embB406 TGC, embB406 TCC, or embB406 GAC codon. These new mutants showed 6-fold and 3- to 3.5-fold increases in the EMB MICs, respectively. In contrast to the embB306 mutants, the isogenic embB497 and embB406 mutants did not have preferential growth in the presence of isoniazid or rifampin (rifampicin) at their MICs. These results demonstrate that individual embCAB mutations confer low to moderate increases in EMB MICs. Discrepancies between the EMB MICs of laboratory mutants and clinical M. tuberculosis strains with identical mutations suggest that clinical EMB resistance is multigenic and that high-level EMB resistance requires mutations in currently unknown loci.
The induction of genetic competence is a strategy used by bacteria to increase their genetic repertoire under stressful environmental conditions. Recently, Streptococcus pneumoniae has been shown to co-ordinate the uptake of transforming DNA with fratricide via increased expression of the peptide pheromone responsible for competence induction. Here, we document that environmental stress-induced expression of the peptide pheromone competence-stimulating peptide (CSP) in the oral pathogen Streptococcus mutans. We showed that CSP is involved in the stress response and determined the CSP-induced regulon in S. mutans by microarray analysis. Contrary to pneumococcus, S. mutans responds to increased concentrations of CSP by cell lysis in only a fraction of the population. We have focused on the mechanism of cell lysis and have identified a novel bacteriocin as the ‘death effector’. Most importantly, we showed that this bacteriocin causes cell death via a novel mechanism of action: intracellular action against self. We have also identified the cognate bacteriocin immunity protein, which resides in a separate unlinked genetic locus to allow its differential regulation. The role of the lytic response in S. mutans competence is also discussed. Together, these findings reveal a novel autolytic pathway in S. mutans which may be involved in the dissemination of fitness-enhancing genes in the oral biofilm.
Extraction of crude membrane fractions with alkaline solutions, such as 100–200 mM Na2CO3 (pH ~11), is often used to solubilize peripheral membrane proteins. Integral membrane proteins are largely retained in membrane pellets. We applied this method to the fractionation of membrane proteins of the plague bacterium Yersinia pestis. Extensive horizontal spot trains were observed in 2-DE gels. The pI values of the most basic spots part of such protein spot trains usually matched the computationally predicted pI values. Regular patterns of decreasing spot pI values and in silico analysis with the software ProMoST suggested `n-1' deamidations of asparagine (N) and/or glutamine (Q) side chains for `n' observed spots of a protein in a given spot train. MALDI-MS analysis confirmed the occurrence of deamidations, particularly in N side chains part of NG dipeptide motifs. In more than ten cases, tandem MS data for tryptic peptides provided strong evidence for deamidations, with y- and b-ion series increased by 1 Da following N-to-D substitutions. Horizontal spot trains in 2-DE gels were rare when alkaline extraction was omitted during membrane protein sample preparation. This study strongly supports the notion that exposure to alkaline pH solutions is a dominant cause of extensive N and Q side chain deamidations in proteins during sample preparation of membrane extracts. The modifications are of non-enzymatic nature and not physiologically relevant. Therefore, quantitative spot differences within spot trains in differential protein display experiments following the aforementioned sample preparation steps need to be interpreted cautiously.
Alkaline membrane extraction; deamidation; membrane proteome; spot train; two-dimensional gel electrophoresis