A conserved tetranucleotide repeat is necessary for wild-type expression of the Moraxella catarrhalis UspA2 protein

Genotypic Characterization of Infectious Spleen and Kidney Necrosis Virus (ISKNV) in Southeast Asian Aquaculture

Infectious spleen and kidney necrosis virus (ISKNV) is a species within the genus Megalocytivirus (family Iridoviridae), which causes high mortality disease in many freshwater and marine fish species. ISKNV was first reported in Asia and is an emerging threat to aquaculture with increasing global distribution, in part due to its presence in ornamental fish with clinical and subclinical infections. The species ISKNV includes three genotypes: red seabream iridovirus (RSIV), turbot reddish body iridovirus (TRBIV), and ISKNV. There is an increasing overlap in the recognized range of susceptible fish hosts and the geographic distribution of these distinct genotypes. To better understand the disease caused by ISKNV, a nucleic acid hybridization capture enrichment was used prior to sequencing to characterize whole genomes from archived clinical specimens of aquaculture and ornamental fish from Southeast Asia (n = 16). The method was suitable for tissue samples containing 2.50 × 104–4.58 × 109 ISKNV genome copies mg−1. Genome sequences determined using the hybridization capture method were identical to those obtained directly from tissues when there was sufficient viral DNA to sequence without enrichment (n = 2). ISKNV genomes from diverse locations, environments, and hosts had very high similarity and matched established genotype classifications (14 ISKNV genotype Clade 1 genomes with >98.81% nucleotide similarity). Conversely, two different genotypes were obtained at the same time and location (RSIV and ISKNV from grouper, Indonesia with 92.44% nucleotide similarity). Gene-by-gene analysis with representative ISKNV genomes identified 59 core genes within the species (>95% amino acid identity). The 14 Clade 1 ISKNV genomes in this study had 100% aa identity for 92–105 of 122 predicted genes. Despite high overall sequence similarity, phylogenetic analyses using single nucleotide polymorphisms differentiated isolates from different host species, country of origin, and time of collection. Whole genome studies of ISKNV and other megalocytiviruses enable genomic epidemiology and will provide information to enhance disease control in aquaculture.

Discovery by metagenomics of a functional tandem repeat sequence that controls gene expression in bacteria

The ability to degrade exogenous compounds is acquired by adaptive processes of microorganisms when they are exposed to compounds that are foreign to their existing enzyme systems. Previously, we reported that simultaneous point mutations and mobile genetic elements cause the evolution and optimization of the degradation systems for aromatic compounds. In the present study, we propose another element with this role—tandem repeats. The novel metagenomic tandem repeat (MTR) sequence T(G/A)ACATG(A/C)T was identified in the 5′-untranslated regions of catechol 2,3-dioxygenase (C23O)-encoding genes by metagenomic analysis. Recombinant Escherichia coli carrying a C23O gene with various numbers of MTRs exhibited increased C23O protein expression and enzyme activity compared with cells expressing the C23O gene without MTRs. Real-time reverse transcription-PCR showed that changes in the numbers of MTRs affected the levels of detectable C23O mRNA in the E. coli host. Furthermore, the mRNAs transcribed from C23O genes containing various numbers of MTRs had longer half-lives than those transcribed from a C23O gene without MTRs. Thus, MTRs would affect the translation efficiency of the gene expression system. MTRs may change the expression levels of their downstream genes for adaptation to a fluctuating environment.

γ-Glutamyltransferase as a Novel Virulence Factor of Acinetobacter baumannii Inducing Alveolar Wall Destruction and Renal Damage in Systemic Disease

A thorough understanding of Acinetobacter baumannii pathogenicity is the key to identifying novel drug targets. In the current study, we characterize the γ-glutamyltransferase enzyme (GGT) as a novel virulence factor. A GGT assay showed that the enzyme is secreted via the type II secretion system and results in higher extracellular activity for the hypervirulent AB5075 than the laboratory-adapted strain American Type Culture Collection 17978. Enzyme-linked immunosorbent assay revealed that the former secretes larger amounts of GGT, and a rifampicin messenger RNA stability study showed that one reason for this could be the longer AB5075 ggt transcript half-life. Infection models confirmed that GGT is required for the virulence of A. baumannii. Finally, we show that clinical isolates with significantly higher extracellular GGT activity resulted in more severe infections, and assay of immune response and tissue damage markers confirm this correlation. The current findings establish for the first time the role of the GGT in the pathogenicity of A. baumannii.

Moraxella catarrhalis phase-variable loci show differences in expression during conditions relevant to disease

Moraxella catarrhalis is a human-adapted, opportunistic bacterial pathogen of the respiratory mucosa. Although asymptomatic colonization of the nasopharynx is common, M. catarrhalis can ascend into the middle ear, where it is a prevalent causative agent of otitis media in children, or enter the lower respiratory tract, where it is associated with acute exacerbations of chronic obstructive pulmonary disease in adults. Phase variation is the high frequency, random, reversible switching of gene expression that allows bacteria to adapt to different host microenvironments and evade host defences, and is most commonly mediated by simple DNA sequence repeats. Bioinformatic analysis of five closed M. catarrhalis genomes identified 17 unique simple DNA sequence repeat tracts that were variable between strains, indicating the potential to mediate phase variable expression of the associated genes. Assays designed to assess simple sequence repeat variation under conditions mimicking host infection demonstrated that phase variation of uspA1 (ubiquitous surface protein A1) from high to low expression occurs over 72 hours of biofilm passage, while phase variation of uspA2 (ubiquitous surface protein A2) to high expression variants occurs during repeated exposure to human serum, as measured by mRNA levels. We also identify and confirm the variable expression of two novel phase variable genes encoding a Type III DNA methyltransferase (modO), and a conserved hypothetical permease (MC25239_RS00020). These data reveal the repertoire of phase variable genes mediated by simple sequence repeats in M. catarrhalis and demonstrate that modulation of expression under conditions mimicking human infection is attributed to changes in simple sequence repeat length.

Persistence of Moraxella catarrhalis in Chronic Obstructive Pulmonary Disease and Regulation of the Hag/MID Adhesin

BACKGROUND

Persistence of bacterial pathogens in the airways has profound consequences on the course and pathogenesis of chronic obstructive pulmonary disease (COPD). Patients with COPD continuously acquire and clear strains of Moraxella catarrhalis, a major pathogen in COPD. Some strains are cleared quickly and some persist for months to years. The mechanism of the variability in duration of persistence is unknown.

METHODS

Guided by genome sequences of selected strains, we studied the expression of Hag/MID, hag/mid gene sequences, adherence to human cells, and autoaggregation in longitudinally collected strains of M. catarrhalis from adults with COPD.

RESULTS

Twenty-eight of 30 cleared strains of M. catarrhalis expressed Hag/MID whereas 17 of 30 persistent strains expressed Hag/MID upon acquisition by patients. All persistent strains ceased expression of Hag/MID during persistence. Expression of Hag/MID in human airways was regulated by slipped-strand mispairing. Virulence-associated phenotypes (adherence to human respiratory epithelial cells and autoaggregation) paralleled Hag/MID expression in airway isolates.

CONCLUSIONS

Most strains of M. catarrhalis express Hag/MID upon acquisition by adults with COPD and all persistent strains shut off expression during persistence. These observations suggest that Hag/MID is important for initial colonization by M. catarrhalis and that cessation of expression facilitates persistence in COPD airways.

The Moraxella catarrhalis phase-variable DNA methyltransferase ModM3 is an epigenetic regulator that affects bacterial survival in an in vivo model of otitis media

Background

Moraxella catarrhalis is a leading cause of otitis media (OM) and chronic obstructive pulmonary disease (COPD). M. catarrhalis contains a Type III DNA adenine methyltransferase (ModM) that is phase-variably expressed (i.e., its expression is subject to random, reversible ON/OFF switching). ModM has six target recognition domain alleles (modM1–6), and we have previously shown that modM2 is the predominant allele, while modM3 is associated with OM. Phase-variable DNA methyltransferases mediate epigenetic regulation and modulate pathogenesis in several bacteria. ModM2 of M. catarrhalis regulates the expression of a phasevarion containing genes important for colonization and infection. Here we describe the phase-variable expression of modM3, the ModM3 methylation site and the suite of genes regulated within the ModM3 phasevarion.

Results

Phase-variable expression of modM3, mediated by variation in length of a 5′-(CAAC)_n-3′ tetranucleotide repeat tract in the open reading frame was demonstrated in M. catarrhalis strain CCRI-195ME with GeneScan fragment length analysis and western immunoblot. We determined that ModM3 is an active N6-adenine methyltransferase that methylates the sequence 5′-AC^m6ATC-3′. Methylation was detected at all 4446 5′-ACATC-3′ sites in the genome when ModM3 is expressed. RNASeq analysis identified 31 genes that are differentially expressed between modM3 ON and OFF variants, including five genes that are involved in the response to oxidative and nitrosative stress, with potential roles in biofilm formation and survival in anaerobic environments. An in vivo chinchilla (Chinchilla lanigera) model of otitis media demonstrated that transbullar challenge with the modM3 OFF variant resulted in an increased middle ear bacterial load compared to a modM3 ON variant. In addition, co-infection experiments with NTHi and M. catarrhalis modM3 ON or modM3 OFF variants revealed that phase variation of modM3 altered survival of NTHi in the middle ear during early and late stage infection.

Conclusions

Phase variation of ModM3 epigenetically regulates the expression of a phasevarion containing multiple genes that are potentially important in the progression of otitis media.

Virulence determinants of Moraxella catarrhalis: distribution and considerations for vaccine development

Moraxella catarrhalis is a human-restricted opportunistic bacterial pathogen of the respiratory mucosa. It frequently colonizes the nasopharynx asymptomatically, but is also an important causative agent of otitis media (OM) in children, and plays a significant role in acute exacerbations of chronic obstructive pulmonary disease (COPD) in adults. As the current treatment options for M. catarrhalis infection in OM and exacerbations of COPD are often ineffective, the development of an efficacious vaccine is warranted. However, no vaccine candidates for M. catarrhalis have progressed to clinical trials, and information regarding the distribution of M. catarrhalis virulence factors and vaccine candidates is inconsistent in the literature. It is largely unknown if virulence is associated with particular strains or subpopulations of M. catarrhalis, or if differences in clinical manifestation can be attributed to the heterogeneous expression of specific M. catarrhalis virulence factors in the circulating population. Further investigation of the distribution of M. catarrhalis virulence factors in the context of carriage and disease is required so that vaccine development may be targeted at relevant antigens that are conserved among disease-causing strains. The challenge of determining which of the proposed M. catarrhalis virulence factors are relevant to human disease is amplified by the lack of a standardized M. catarrhalis typing system to facilitate direct comparisons of worldwide isolates. Here we summarize and evaluate proposed relationships between M. catarrhalis subpopulations and specific virulence factors in the context of colonization and disease, as well as the current methods used to infer these associations.

Isogenic mutations in the Moraxella catarrhalis CydDC system display pleiotropic phenotypes and reveal the role of a palindrome sequence in its transcriptional regulation

Moraxella catarrhalis is becoming an important human respiratory tract pathogen affecting significant proportions from the population. However, still little is known about its physiology and molecular regulation. To this end, the CydDC, which is a heterodimeric ATP binding cassette transporter that has been shown to contribute to the maintenance of the redox homeostasis across the periplasm in other Gram-negative bacteria, is studied here. Amino acids multiple sequence alignments indicated that M. catarrhalis CydC is different from the CydC proteins of the bacterial species in which this system has been previously studied. These findings prompted further interest in studying this system in M. catarrhalis. Isogenic mutant in the CydDC system showed suppression in growth rate, hypersensitivity to oxidative and reductive stress and increased accumulation of intracellular cysteine levels. In addition, the growth of cydC^- mutant exhibited hypersensitivity to exogenous cysteine; however, it did not display a significant difference from its wild-type counterpart in the murine pulmonary clearance model. Moreover, a palindrome was detected 94bp upstream of the cydD ORF suggesting it might act as a potential regulatory element. Real-time reverse transcription-PCR analysis showed that deletion/change in the palindrome resulted into alterations in the transcription levels of cydC. A better understanding of such system and its regulation helps in developing better ways to combat M. catarrhalis infections.

Potential impact of a Moraxella catarrhalis vaccine in COPD

Moraxella catarrhalis is the second most common cause of exacerbations in adults with COPD, resulting in enormous morbidity and mortality in this clinical setting. Vaccine development for M. catarrhalis has lagged behind the other two important causes of exacerbations in COPD, nontypeable Haemophilus influenzae and Streptococcus pneumoniae. While no licensed vaccine is currently available for M. catarrhalis, several promising candidate vaccine antigens have been identified and characterized and are close to entering clinical trials. Key steps that are required to advance vaccines for M. catarrhalis along the translational pipeline include standardization of assay systems to assess candidate antigens, identification of a reliable correlate of protection and expansion of partnerships between industry, academia and government to overcome regulatory hurdles. A vaccine to prevent M. catarrhalis infections in COPD would have a major impact in reducing morbidity, mortality and healthcare costs in COPD.

Immunoinformatics Identifies a Lactoferrin Binding Protein A Peptide as a Promising Vaccine With a Global Protective Prospective Against Moraxella catarrhalis

BACKGROUND

Moraxella catarrhalis is an established pathogen that is causing substantial infections to both children and adults. However, so far there is no effective vaccine to halt the spread of these infections.

METHODS

Immunoinformatics tools were used to predict M. catarrhalis epitopes that could offer immunoprotection among major proportions of human populations worldwide. Mice were immunized with the best 3 peptides and then challenged with M. catarrhalis in the pulmonary clearance model. Finally, antibodies against these epitopes were detected in humans.

RESULTS

Immunoinformatics analyses identified 44 epitopes that are predicted to be good major histocompatibility complex class II binders and at the same time show high population coverage worldwide. After intraperitoneal immunization of mice with the best 3 peptides, peptide A, derived from lactoferrin-binding protein A, showed superior activity in immunogenicity and in clearing M. catarrhalis from mouse lungs. Higher clearance was obtained by combining intraperitoneal and intranasal immunization. In the serum samples from children with otitis media infected with M. catarrhalis, antibody levels against peptide A were significantly lower than in samples from children without otitis media.

CONCLUSIONS

Peptide A is the first promising peptide-based vaccine against M. catarrhalis Immunoinformatics predicts that it should have a global protection around the world.

Abundant Intergenic TAACTGA Direct Repeats and Putative Alternate RNA Polymerase β' Subunits in Marine Beggiatoaceae Genomes: Possible Regulatory Roles and Origins

The genome sequences of several giant marine sulfur-oxidizing bacteria present evidence of a possible post-transcriptional regulatory network that may have been transmitted to or from two distantly related bacteria lineages. The draft genome of a Cand. “Maribeggiatoa” filament from the Guaymas Basin (Gulf of California, Mexico) seafloor contains 169 sets of TAACTGA direct repeats and one indirect repeat, with two to six copies per set. Related heptamers are rarely or never found as direct repeats. TAACTGA direct repeats are also found in some other Beggiatoaceae, Thiocystis violascens, a range of Cyanobacteria, and five Bacteroidetes. This phylogenetic distribution suggests they may have been transmitted horizontally, but no mechanism is evident. There is no correlation between total TAACTGA occurrences and repeats per genome. In most species the repeat units are relatively short, but longer arrays of up to 43 copies are found in several Bacteroidetes and Cyanobacteria. The majority of TAACTGA repeats in the Cand. “Maribeggiatoa” Orange Guaymas (BOGUAY) genome are within several nucleotides upstream of a putative start codon, suggesting they may be binding sites for a post-transcriptional regulator. Candidates include members of the ribosomal protein S1, Csp (cold shock protein), and Csr (carbon storage regulator) families. No pattern was evident in the predicted functions of the open reading frames (ORFs) downstream of repeats, but some encode presumably essential products such as ribosomal proteins. Among these is an ORF encoding a possible alternate or modified RNA polymerase beta prime subunit, predicted to have the expected subunit interaction domains but lacking most catalytic residues. A similar ORF was found in the Thioploca ingrica draft genome, but in no others. In both species they are immediately upstream of putative sensor kinase genes with nearly identical domain structures. In the marine Beggiatoaceae, a role for the TAACTGA repeats in translational regulation is suggested. More speculatively, the putative alternate RNA polymerase subunit could be a negative transcriptional regulator.

Vaccine targets against Moraxella catarrhalis

INTRODUCTION

Moraxella catarrhalis is a prominent pathogen that causes acute otitis media in children and lower respiratory tract infections in adults, resulting in a significant socioeconomic burden on healthcare systems globally. No vaccine is currently available for M. catarrhalis. Promising M. catarrhalis target antigens have been characterized in animal models and should soon enter human clinical trials.

AREAS COVERED

This review discusses the detailed features and research status of current candidate target antigens for an M. catarrhalis vaccine. The approaches for assessing M. catarrhalis vaccine efficacy are also discussed.

EXPERT OPINION

Targeting the key molecules contributing to serum resistance may be a viable strategy to identify effective vaccine targets among M. catarrhalis antigens. Elucidating the role and mechanisms of the serum and mucosal immune responses to M. catarrhalis is significant for vaccine target selection, testing and evaluation. Developing animal models closely simulating M. catarrhalis-caused human respiratory diseases is of great benefit in better understanding pathogenesis and evaluating vaccine efficacy. Carrying out clinical trials will be a landmark in the progress of M. catarrhalis vaccine research. Combined multicomponent vaccines will be a focus of future M. catarrhalis vaccine studies.

A Moraxella catarrhalis two-component signal transduction system necessary for growth in liquid media affects production of two lysozyme inhibitors

There are a paucity of data concerning gene products that could contribute to the ability of Moraxella catarrhalis to colonize the human nasopharynx. Inactivation of a gene (mesR) encoding a predicted response regulator of a two-component signal transduction system in M. catarrhalis yielded a mutant unable to grow in liquid media. This mesR mutant also exhibited increased sensitivity to certain stressors, including polymyxin B, SDS, and hydrogen peroxide. Inactivation of the gene (mesS) encoding the predicted cognate sensor (histidine) kinase yielded a mutant with the same inability to grow in liquid media as the mesR mutant. DNA microarray and real-time reverse transcriptase PCR analyses indicated that several genes previously shown to be involved in the ability of M. catarrhalis to persist in the chinchilla nasopharynx were upregulated in the mesR mutant. Two other open reading frames upregulated in the mesR mutant were shown to encode small proteins (LipA and LipB) that had amino acid sequence homology to bacterial adhesins and structural homology to bacterial lysozyme inhibitors. Inactivation of both lipA and lipB did not affect the ability of M. catarrhalis O35E to attach to a human bronchial epithelial cell line in vitro. Purified recombinant LipA and LipB fusion proteins were each shown to inhibit human lysozyme activity in vitro and in saliva. A lipA lipB deletion mutant was more sensitive than the wild-type parent strain to killing by human lysozyme in the presence of human apolactoferrin. This is the first report of the production of lysozyme inhibitors by M. catarrhalis.

A repetitive DNA element regulates expression of the Helicobacter pylori sialic acid binding adhesin by a rheostat-like mechanism

During persistent infection, optimal expression of bacterial factors is required to match the ever-changing host environment. The gastric pathogen Helicobacter pylori has a large set of simple sequence repeats (SSR), which constitute contingency loci. Through a slipped strand mispairing mechanism, the SSRs generate heterogeneous populations that facilitate adaptation. Here, we present a model that explains, in molecular terms, how an intergenically located T-tract, via slipped strand mispairing, operates with a rheostat-like function, to fine-tune activity of the promoter that drives expression of the sialic acid binding adhesin, SabA. Using T-tract variants, in an isogenic strain background, we show that the length of the T-tract generates multiphasic output from the sabA promoter. Consequently, this alters the H. pylori binding to sialyl-Lewis x receptors on gastric mucosa. Fragment length analysis of post-infection isolated clones shows that the T-tract length is a highly variable feature in H. pylori. This mirrors the host-pathogen interplay, where the bacterium generates a set of clones from which the best-fit phenotypes are selected in the host. In silico and functional in vitro analyzes revealed that the length of the T-tract affects the local DNA structure and thereby binding of the RNA polymerase, through shifting of the axial alignment between the core promoter and UP-like elements. We identified additional genes in H. pylori, with T- or A-tracts positioned similar to that of sabA, and show that variations in the tract length likewise acted as rheostats to modulate cognate promoter output. Thus, we propose that this generally applicable mechanism, mediated by promoter-proximal SSRs, provides an alternative mechanism for transcriptional regulation in bacteria, such as H. pylori, which possesses a limited repertoire of classical trans-acting regulatory factors.

Identification of an outer membrane lipoprotein involved in nasopharyngeal colonization by Moraxella catarrhalis in an animal model

Colonization of the human nasopharynx by Moraxella catarrhalis is presumed to involve attachment of this bacterium to the mucosa. DNA microarray analysis was used to determine whether attachment of M. catarrhalis to human bronchial epithelial (HBE) cells in vitro affected gene expression in this bacterium. Attachment affected expression of at least 454 different genes, with 163 being upregulated and 291 being downregulated. Among the upregulated genes was one (ORF113) previously annotated as encoding a protein with some similarity to outer membrane protein A (OmpA). The protein encoded by ORF113 was predicted to have a signal peptidase II cleavage site, and globomycin inhibition experiments confirmed that this protein was indeed a lipoprotein. The ORF113 protein also contained a predicted peptidoglycan-binding domain in its C-terminal half. The use of mutant and recombinant M. catarrhalis strains confirmed that the ORF113 protein was present in outer membrane preparations, and this protein was also shown to be at least partially exposed on the bacterial cell surface. A mutant unable to produce the ORF113 protein showed little or no change in its growth rate in vitro, in its ability to attach to HBE cells in vitro, or in its autoagglutination characteristics, but it did exhibit a reduced ability to survive in the chinchilla nasopharynx. This is the first report of a lipoprotein essential to the ability of M. catarrhalis to persist in an animal model.

A variable homopolymeric G-repeat defines small RNA-mediated posttranscriptional regulation of a chemotaxis receptor in Helicobacter pylori

Phase variation of hypermutable simple sequence repeats (SSRs) is a widespread and stochastic mechanism to generate phenotypic variation within a population and thereby contributes to host adaptation of bacterial pathogens. Although several examples of SSRs that affect transcription or coding potential have been reported, we now show that a SSR also impacts small RNA-mediated posttranscriptional regulation. Based on in vitro and in vivo analyses, we demonstrate that a variable homopolymeric G-repeat in the leader of the TlpB chemotaxis receptor mRNA of the human pathogen Helicobacter pylori is directly targeted by a small RNA (sRNA), RepG (Regulator of polymeric G-repeats). Whereas RepG sRNA is highly conserved, the tlpB G-repeat length varies among diverse H. pylori strains, resulting in strain-specific RepG-mediated tlpB regulation. Based on modification of the G-repeat length within one strain, we demonstrate that the G-repeat length determines posttranscriptional regulation and can mediate both repression and activation of tlpB through RepG. In vitro translation assays show that this regulation occurs at the translational level and that RepG influences tlpB translation dependent on the G-repeat length. In contrast to the digital ON-OFF switches through frame-shift mutations within coding sequences, such modulation of posttranscriptional regulation allows for a gradual control of gene expression. This connection to sRNA-mediated posttranscriptional regulation might also apply to other genes with SSRs, which could be targeting sites of cis- or trans-encoded sRNAs, and thereby could facilitate host adaptation through sRNA-mediated fine-tuning of virulence gene expression.

The role of variable DNA tandem repeats in bacterial adaptation

DNA tandem repeats (TRs), also designated as satellite DNA, are inter- or intragenic nucleotide sequences that are repeated two or more times in a head-to-tail manner. Because TR tracts are prone to strand-slippage replication and recombination events that cause the TR copy number to increase or decrease, loci containing TRs are hypermutable. An increasing number of examples illustrate that bacteria can exploit this instability of TRs to reversibly shut down or modulate the function of specific genes, allowing them to adapt to changing environments on short evolutionary time scales without an increased overall mutation rate. In this review, we discuss the prevalence and distribution of inter- and intragenic TRs in bacteria and the mechanisms of their instability. In addition, we review evidence demonstrating a role of TR variations in bacterial adaptation strategies, ranging from immune evasion and tissue tropism to the modulation of environmental stress tolerance. Nevertheless, while bioinformatic analysis reveals that most bacterial genomes contain a few up to several dozens of intra- and intergenic TRs, only a small fraction of these have been functionally studied to date.

Physiologic cold shock of Moraxella catarrhalis affects the expression of genes involved in the iron acquisition, serum resistance and immune evasion

Background

Moraxella catarrhalis, a major nasopharyngeal pathogen of the human respiratory tract, is exposed to rapid downshifts of environmental temperature when humans breathe cold air. It was previously shown that the prevalence of pharyngeal colonization and respiratory tract infections caused by M. catarrhalis are greatest in winter. The aim of this study was to investigate how M. catarrhalis uses the physiologic exposure to cold air to upregulate pivotal survival systems in the pharynx that may contribute to M. catarrhalis virulence.

Results

A 26°C cold shock induces the expression of genes involved in transferrin and lactoferrin acquisition, and enhances binding of these proteins on the surface of M. catarrhalis. Exposure of M. catarrhalis to 26°C upregulates the expression of UspA2, a major outer membrane protein involved in serum resistance, leading to improved binding of vitronectin which neutralizes the lethal effect of human complement. In contrast, cold shock decreases the expression of Hemagglutinin, a major adhesin, which mediates B cell response, and reduces immunoglobulin D-binding on the surface of M. catarrhalis.

Conclusion

Cold shock of M. catarrhalis induces the expression of genes involved in iron acquisition, serum resistance and immune evasion. Thus, cold shock at a physiologically relevant temperature of 26°C induces in M. catarrhalis a complex of adaptive mechanisms that enables the bacterium to target their host cellular receptors or soluble effectors and may contribute to enhanced growth, colonization and virulence.

Temporal development of the humoral immune response to surface antigens of Moraxella catarrhalis in young infants

The primary Moraxella catarrhalis-specific humoral immune response, and its association with nasopharyngeal colonization, was studied in a cohort of infants from birth to 2 years of age. Results indicated that the levels of antigen-specific IgG, IgA and IgM showed extensive inter-individual variability over time, with IgM and IgA levels to all 9 recombinant domains, from 7 different OMPs, being relatively low throughout the study period. In contrast, the level of antigen-specific IgG was significantly higher for the recombinant domains Hag³⁵⁸⁻⁸⁵³, MID⁷⁶⁴⁻⁹¹³, MID⁹⁶²⁻¹²⁰⁰, UspA1⁵⁵⁷⁻⁷⁰⁴ and UspA2¹⁶⁵⁻³¹⁸ in cord blood compared to 6 months of age (P ≤ 0.001). This was a most likely a consequence of maternal transmission of antigen-specific IgG to newborn babies, possibly indicating a future role for these 3 surface antigens in the development of an effective humoral immune response to M. catarrhalis. Finally, at 2 years of age, the levels of antigen-specific IgG still remained far below that obtained from cord blood samples, indicating that the immune response to M. catarrhalis has not matured at 2 years of age. We provide evidence that a humoral antibody response to OMPs UspA1, UspA2 and Hag/MID may play a role in the immune response to community acquired M. catarrhalis colonization events.

Molecular aspects of Moraxella catarrhalis pathogenesis

In recent years, Moraxella catarrhalis has established its position as an important human mucosal pathogen, no longer being regarded as just a commensal bacterium. Further, current research in the field has led to a better understanding of the molecular mechanisms involved in M. catarrhalis pathogenesis, including mechanisms associated with cellular adherence, target cell invasion, modulation of the host's immune response, and metabolism. Additionally, in order to be successful in the host, M. catarrhalis has to be able to interact and compete with the commensal flora and overcome stressful environmental conditions, such as nutrient limitation. In this review, we provide a timely overview of the current understanding of the molecular mechanisms associated with M. catarrhalis virulence and pathogenesis.

Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis

Background

Bacteriocins are antimicrobial proteins and peptides ribosomally synthesized by some bacteria which can effect both intraspecies and interspecies killing.

Results

Moraxella catarrhalis strain E22 containing plasmid pLQ510 was shown to inhibit the growth of M. catarrhalis strain O35E. Two genes (mcbA and mcbB) in pLQ510 encoded proteins predicted to be involved in the secretion of a bacteriocin. Immediately downstream from these two genes, a very short ORF (mcbC) encoded a protein which had some homology to double-glycine bacteriocins produced by other bacteria. A second very short ORF (mcbI) immediately downstream from mcbC encoded a protein which had no significant similarity to other proteins in the databases. Cloning and expression of the mcbI gene in M. catarrhalis O35E indicated that this gene encoded the cognate immunity factor. Reverse transcriptase-PCR was used to show that the mcbA, mcbB, mcbC, and mcbI ORFs were transcriptionally linked. This four-gene cluster was subsequently shown to be present in the chromosome of several M. catarrhalis strains including O12E. Inactivation of the mcbA, mcbB, or mcbC ORFs in M. catarrhalis O12E eliminated the ability of this strain to inhibit the growth of M. catarrhalis O35E. In co-culture experiments involving a M. catarrhalis strain containing the mcbABCI locus and one which lacked this locus, the former strain became the predominant member of the culture after overnight growth in broth.

Conclusion

This is the first description of a bacteriocin and its cognate immunity factor produced by M. catarrhalis. The killing activity of the McbC protein raises the possibility that it might serve to lyse other M. catarrhalis strains that lack the mcbABCI locus, thereby making their DNA available for lateral gene transfer.

Laboratory Maintenance of Moraxella catarrhalis

Moraxella catarrhalis is a Gram-negative bacterium that has recently emerged as the third leading cause of bacterial ear infections in children. This organism is also responsible for a variety of upper respiratory tract illnesses in adults, including approximately 10% of all cases of respiratory exacerbations in patients with chronic obstructive pulmonary disease (COPD). There is interest in studying M. catarrhalis for vaccine development, and this unit provides guidelines for the laboratory maintenance of the organism. The three Basic Protocols presented in this unit describe how to culture and prepare M. catarrhalis cells for use in experiments pertaining to various biological aspects of this important respiratory pathogen.

Moraxella catarrhalis expresses an unusual Hfq protein

The Hfq protein is recognized as a global regulatory molecule that facilitates certain RNA-RNA interactions in bacteria. BLAST analysis identified a 630-nucleotide open reading frame in the genome of Moraxella catarrhalis ATCC 43617 that was highly conserved among M. catarrhalis strains and which encoded a predicted protein with significant homology to the Hfq protein of Escherichia coli. This protein, containing 210 amino acids, was more than twice as large as the Hfq proteins previously described for other bacteria. The C-terminal half of the M. catarrhalis Hfq protein was very hydrophilic and contained two different types of amino acid repeats. A mutation in the M. catarrhalis hfq gene affected both the growth rate of this organism and its sensitivity to at least two different types of stress in vitro. Provision of the wild-type M. catarrhalis hfq gene in trans eliminated these phenotypic differences in the hfq mutant. This M. catarrhalis hfq mutant exhibited altered expression of some cell envelope proteins relative to the wild-type parent strain and also had a growth advantage in a continuous flow biofilm system. The presence of the wild-type M. catarrhalis hfq gene in trans in an E. coli hfq mutant fully reversed the modest growth deficiency of this E. coli mutant and partially reversed the stress sensitivity of this E. coli mutant to methyl viologen. The use of an electrophoretic mobility shift assay showed that this M. catarrhalis Hfq protein could bind RNA derived from a gene whose expression was altered in the M. catarrhalis hfq mutant.

Moraxella catarrhalis synthesizes an autotransporter that is an acid phosphatase

Moraxella catarrhalis O35E was shown to synthesize a 105-kDa protein that has similarity to both acid phosphatases and autotransporters. The N-terminal portion of the M. catarrhalis acid phosphatase A (MapA) was most similar (the BLAST probability score was 10(-10)) to bacterial class A nonspecific acid phosphatases. The central region of the MapA protein had similarity to passenger domains of other autotransporter proteins, whereas the C-terminal portion of MapA resembled the translocation domain of conventional autotransporters. Cloning and expression of the M. catarrhalis mapA gene in Escherichia coli confirmed the presence of acid phosphatase activity in the MapA protein. The MapA protein was shown to be localized to the outer membrane of M. catarrhalis and was not detected either in the soluble cytoplasmic fraction from disrupted M. catarrhalis cells or in the spent culture supernatant fluid from M. catarrhalis. Use of the predicted MapA translocation domain in a fusion construct with the passenger domain from another predicted M. catarrhalis autotransporter confirmed the translocation ability of this MapA domain. Inactivation of the mapA gene in M. catarrhalis strain O35E reduced the acid phosphatase activity expressed by this organism, and this mutation could be complemented in trans with the wild-type mapA gene. Nucleotide sequence analysis of the mapA gene from six M. catarrhalis strains showed that this protein was highly conserved among strains of this pathogen. Site-directed mutagenesis of a critical histidine residue (H233A) in the predicted active site of the acid phosphatase domain in MapA eliminated acid phosphatase activity in the recombinant MapA protein. This is the first description of an autotransporter protein that expresses acid phosphatase activity.