scholarly journals Coupled Phase-Variable Expression and Epitope Masking of Selective Surface Lipoproteins Increase Surface Phenotypic Diversity in Mycoplasma hominis

2001 ◽  
Vol 69 (8) ◽  
pp. 5177-5181 ◽  
Author(s):  
Qijing Zhang ◽  
Kim S. Wise
Keyword(s):  
Membrane Protein ◽  
High Frequency ◽  
Phenotypic Diversity ◽  
Phase Variation ◽  
Mycoplasma Hominis ◽  
Phase Variable ◽  
Variable Expression ◽  
Adaptive Capabilities ◽  
Frequency Phase

ABSTRACT A new mechanism expanding mycoplasmal surface diversity is described. Exposure of surface epitopes on a constitutively expressed membrane protein (P56) of Mycoplasma hominis was subject to high-frequency phase variation due to phase-variable expression of the P120 antigen and its selective masking of P56 epitopes. Phase-variable masking may confer previously unrealized adaptive capabilities on mycoplasmas.

scholarly journals High-frequency phase-switching of modB methylase is associated with phenotypic ceftriaxone susceptibility in Neisseria gonorrhoeae

2020 ◽  
Author(s):  
Ola B Brynildsrud ◽  
Magnus N Osnes ◽  
Kevin C Ma ◽  
Yonatan H Grad ◽  
Michael Koomey ◽  
...  
Keyword(s):  
High Frequency ◽  
Genetic Basis ◽  
Meta Analysis ◽  
Phase Variation ◽  
Phase Variable ◽  
Phase Switching ◽  
Expression Of Genes ◽  
Genome Wide ◽  
Restriction Modification ◽  
Frequency Phase

AbstractThe gonococcal adenine methylases modA and modB, belonging to separate Type III restriction modification systems, are phase variable and could thus enable rapid adaptation to changing environments. However, the frequency of phase variation across transmission chains and the phenotypic impact of phase variation are largely unknown.Here we show that the repeat tracts enabling phase variation expand and contract at high rates in both modA and modB. For modB, multiple ON/OFF transition events were identified over the course of a single outbreak.A mixed effects model using population samples from Norway and a global meta-analysis collection indicates that modB in the OFF state is predictive of moderately decreased ceftriaxone susceptibility. Our findings suggest that modB orchestration of genome-wide 6-methyladenine modification controls the expression of genes modulating ceftriaxone susceptibility.ImportanceDespite significant progress, our current understanding of the genetic basis of antibiotic susceptibility remains incomplete. The gonococcal methylase modB is phase variable, meaning that it can be switched ON or OFF via contraction or expansion of a repeat tract in the gene during replication. We find that transitions between the ON and OFF state occur at high frequency. Furthermore, isolates harbouring modB in a configuration predicted to be inactive had decreased susceptibility to ceftriaxone, an antibiotic used to treat gonorrhea. This finding improves understanding of the genetic underpinnings of antibiotic resistance, but further work is needed to elucidate the mechanics and broader phenotypic effects of epigenetic modifications and transcription.

scholarly journals Identification and Characterization ofpptA: a Gene Involved in the Phase-Variable Expression ofPhosphorylcholine on Pili of Neisseriameningitidis

2003 ◽  
Vol 71 (12) ◽  
pp. 6892-6898 ◽  
Author(s):  
Matthew J. Warren ◽  
Michael P. Jennings
Keyword(s):  
High Frequency ◽  
Phase Variation ◽  
Open Reading Frames ◽  
Phase Variable ◽  
Dna Transformation ◽  
Twitching Motility ◽  
Variable Expression ◽  
Factors Associated ◽  
Identification And Characterization ◽  
Reading Frames

ABSTRACT Pili of pathogenic Neisseria are major virulence factors associated with adhesion, cytotoxicity, twitching motility, autoaggregation, and DNA transformation. Pili are modified posttranslationally by the addition of phosphorylcholine. However, no genes involved in either the biosynthesis or the transfer of phosphorylcholine in Neisseria meningitidis have been identified. In this study, we identified five candidate open reading frames (ORFs) potentially involved in the biosynthesis or transfer of phosphorylcholine to pilin in N. meningitidis. Insertional mutants were constructed for each ORF in N. meningitidis strain C311#3 to determine their effect on phosphorylcholine expression. The effect of the mutant ORFs on the modification by phosphorylcholine was analyzed by Western analysis with phosphorylcholine-specific monoclonal antibody TEPC-15. Analysis of the mutants showed that ORF NMB0415, now defined as pptA (pilin phosphorylcholine transferase A), is involved in the addition of phosphorylcholine to pilin in N. meningitidis. Additionally, the phase variation (high frequency on-off switching of expression) of phosphorylcholine on pilin is due to changes in a homopolymeric guanosine tract in pptA.

scholarly journals Elucidation of the Monoclonal Antibody 5G8-Reactive, Virulence-Associated Lipopolysaccharide Epitope of Haemophilus influenzae and Its Role in Bacterial Resistance to Complement-Mediated Killing

2005 ◽  
Vol 73 (4) ◽  
pp. 2213-2221 ◽  
Author(s):  
Ruth Griffin ◽  
Andrew D. Cox ◽  
Katherine Makepeace ◽  
James C. Richards ◽  
E. Richard Moxon ◽  
...  
Keyword(s):  
Monoclonal Antibody ◽  
Haemophilus Influenzae ◽  
Bacterial Resistance ◽  
Inner Core ◽  
Phase Variation ◽  
Phase Variable ◽  
Type B ◽  
Variable Expression ◽  
Virulent Type ◽  
Unknown Structure

ABSTRACT The phase-variable locus lex2 is required for expression of a Haemophilus influenzae lipopolysaccharide (LPS) epitope of previously unknown structure. This epitope, which is reactive with monoclonal antibody (MAb) 5G8, has been associated with virulence of type b strains. When strain RM118 (from the same source as strain Rd), in which the lex2 locus and MAb 5G8 reactivity are absent, was transformed with lex2 DNA, transformants that were reactive with MAb 5G8 were obtained. Surprisingly, the 5G8 reactivity of these transformants was phase variable, although the lex2 locus lacked tetrameric repeats and was constitutively expressed. This phase variation was shown to be the result of phase-variable expression of phosphorylcholine (PCho) such that MAb 5G8 reacted only in the absence of PCho. Structural analysis showed that, compared to RM118, the lex2 transformant had acquired a tetrasaccharide, Gal-α1,4-Gal-β1,4-Glc-β1,4-Glc-β1,4, linked to the proximal heptose (HepI). A terminal GalNAc was detected in a minority of glycoforms. LPS derived from a mutant of RM7004, a virulent type b strain which naturally expresses lex2 and has LPS containing the same tetrasaccharide linked to HepI as the sole oligosaccharide extension from the inner core, confirmed that GalNAc is not a part of the MAb 5G8-reactive epitope. Thus, MAb 5G8 specifically binds to the structure Gal-α1,4-Gal-β1,4-Glc-β1,4-Glc-β attached via a 1,4 linkage to HepI of H. influenzae LPS, and we show that the ability to synthesize this novel tetrasaccharide was associated with enhanced bacterial resistance to complement-mediated killing.

scholarly journals Phase-Variable Expression of an Operon Encoding Extracellular Alkaline Protease, a Serine Protease Homolog, and Lipase in Pseudomonas brassicacearum

2001 ◽  
Vol 183 (6) ◽  
pp. 2117-2120 ◽  
Author(s):  
Philippe Chabeaud ◽  
Arjan de Groot ◽  
Wilbert Bitter ◽  
Jan Tommassen ◽  
Thierry Heulin ◽  
...  
Keyword(s):  
Serine Protease ◽  
Lipase Activity ◽  
Alkaline Protease ◽  
Phase Variation ◽  
Extracellular Protease ◽  
Type I ◽  
Phase Variable ◽  
Gene Fusions ◽  
Variable Expression ◽  
Pseudomonas Brassicacearum

ABSTRACT The rhizobacterium Pseudomonas brassicacearum forms phenotypic variants which do not show extracellular protease and lipase activity. The operon encoding these enzymes, a serine protease homolog, and a type I secretion machinery was characterized. Transcriptional lacZ gene fusions revealed that the expression of the operon is under the control of phase variation.

scholarly journals A surface epitope undergoing high-frequency phase variation is shared by Mycoplasma gallisepticum and Mycoplasma bovis.

1994 ◽  
Vol 62 (11) ◽  
pp. 4962-4968 ◽  
Author(s):  
D Yogev ◽  
D Menaker ◽  
K Strutzberg ◽  
S Levisohn ◽  
H Kirchhoff ◽  
...  
Keyword(s):  
High Frequency ◽  
Phase Variation ◽  
Mycoplasma Gallisepticum ◽  
Mycoplasma Bovis ◽  
Frequency Phase

scholarly journals The Major Phase-Variable Outer Membrane Protein ofEscherichia coli Structurally Resembles the Immunoglobulin A1 Protease Class of Exported Protein and Is Regulated by a Novel Mechanism Involving Dam and OxyR

1999 ◽  
Vol 181 (7) ◽  
pp. 2132-2141 ◽  
Author(s):  
Ian R. Henderson ◽  
Peter Owen
Keyword(s):  
Membrane Protein ◽  
Outer Membrane ◽  
Dna Sequences ◽  
Outer Membrane Protein ◽  
Signal Sequence ◽  
Regulatory Region ◽  
Specific Antigen ◽  
Phase Variation ◽  
Phase Variable ◽  
Phase Switching

ABSTRACT Here we report the characterization of an Escherichia coli gene (agn43) which encodes the principal phase-variable outer membrane protein termed antigen 43 (Ag43). Theagn43 gene encodes a precursor protein of 107 kDa containing a 52-amino-acid signal sequence. Posttranslational processing generates an α43 subunit (predictedM r of 49,789) and a C-terminal domain (β43) with features typical of a bacterial integral outer membrane protein (predicted M r of 51,642). Secondary structure analysis predicts that β43 exists as an 18-stranded β barrel and that Ag43 shows structural organization closely resembling that of immunoglobulin A1 protease type of exoprotein produced by pathogenic Neisseria andHaemophilus spp. The correct processing of the polyprotein to α43 and β43 in OmpT, OmpP, and DegP protease-deficient E. coli strains points to an autocatalytic cleavage mechanism, a hypothesis supported by the occurrence of an aspartyl protease active site within α43. Ag43, a species-specific antigen, possesses two RGD motifs of the type implicated in binding to human integrins. The mechanism of reversible phase variation was studied by immunochemical analysis of a panel of well-defined regulatory mutants and by analysis of DNA sequences upstream of agn43. Evidence strongly suggests that phase variation is regulated by both deoxyadenosine methylase (Dam) and by OxyR. Thus, oxyR mutants are locked on for Ag43 expression, whereas dam mutants are locked off for Ag43 expression. We propose a novel mechanism for the regulation of phase switching in which OxyR competes with Dam for unmethylated GATC sites in the regulatory region of the agn43 gene.

scholarly journals Nonselective Bottlenecks Control the Divergence and Diversification of Phase-Variable Bacterial Populations

mBio ◽  
2017 ◽  
Vol 8 (2) ◽  
Author(s):  
Jack Aidley ◽  
Shweta Rajopadhye ◽  
Nwanekka M. Akinyemi ◽  
Lea Lango-Scholey ◽  
Christopher D. Bayliss
Keyword(s):  
Experimental Data ◽  
Campylobacter Jejuni ◽  
High Frequency ◽  
Phase Variation ◽  
Population Diversity ◽  
Surface Structures ◽  
Phase Variable ◽  
Stochastic Variation ◽  
Food Borne ◽  
Simple Sequence

ABSTRACT Phase variation occurs in many pathogenic and commensal bacteria and is a major generator of genetic variability. A putative advantage of phase variation is to counter reductions in variability imposed by nonselective bottlenecks during transmission. Genomes of Campylobacter jejuni, a widespread food-borne pathogen, contain multiple phase-variable loci whose rapid, stochastic variation is generated by hypermutable simple sequence repeat tracts. These loci can occupy a vast number of combinatorial expression states (phasotypes) enabling populations to rapidly access phenotypic diversity. The imposition of nonselective bottlenecks can perturb the relative frequencies of phasotypes, changing both within-population diversity and divergence from the initial population. Using both in vitro testing of C. jejuni populations and a simple stochastic simulation of phasotype change, we observed that single-cell bottlenecks produce output populations of low diversity but with bimodal patterns of either high or low divergence. Conversely, large bottlenecks allow divergence only by accumulation of diversity, while interpolation between these extremes is observed in intermediary bottlenecks. These patterns are sensitive to the genetic diversity of initial populations but stable over a range of mutation rates and number of loci. The qualitative similarities of experimental and in silico modeling indicate that the observed patterns are robust and applicable to other systems where localized hypermutation is a defining feature. We conclude that while phase variation will maintain bacterial population diversity in the face of intermediate bottlenecks, narrow transmission-associated bottlenecks could produce host-to-host variation in bacterial phenotypes and hence stochastic variation in colonization and disease outcomes. IMPORTANCE Transmission and within-host spread of pathogenic organisms are associated with selective and nonselective bottlenecks that significantly reduced population diversity. In several bacterial pathogens, hypermutable mechanisms have evolved that mediate high-frequency reversible switching of specific phenotypes, such as surface structures, and hence counteract bottleneck-associated reductions in population diversity. Here, we investigated how combinations of hypermutable simple sequence repeats interact with nonselective bottlenecks by using a stochastic computer model and experimental data for Campylobacter jejuni, a food-borne pathogen. We find that bottleneck size qualitatively alters the output populations, with large bottlenecks maintaining population diversity while small bottlenecks produce dramatic shifts in the prevalence of particular variants. We conclude that narrow bottlenecks are capable of producing host-to-host variation in repeat-controlled bacterial phenotypes, leading to a potential for stochastic person-to-person variations in disease outcome for C. jejuni and other organisms with similar hypermutable mechanisms. IMPORTANCE Transmission and within-host spread of pathogenic organisms are associated with selective and nonselective bottlenecks that significantly reduced population diversity. In several bacterial pathogens, hypermutable mechanisms have evolved that mediate high-frequency reversible switching of specific phenotypes, such as surface structures, and hence counteract bottleneck-associated reductions in population diversity. Here, we investigated how combinations of hypermutable simple sequence repeats interact with nonselective bottlenecks by using a stochastic computer model and experimental data for Campylobacter jejuni, a food-borne pathogen. We find that bottleneck size qualitatively alters the output populations, with large bottlenecks maintaining population diversity while small bottlenecks produce dramatic shifts in the prevalence of particular variants. We conclude that narrow bottlenecks are capable of producing host-to-host variation in repeat-controlled bacterial phenotypes, leading to a potential for stochastic person-to-person variations in disease outcome for C. jejuni and other organisms with similar hypermutable mechanisms.

scholarly journals Genotypic and Phenotypic Characterization of theO-Linked Protein Glycosylation System Reveals High Glycan Diversity in Paired Meningococcal Carriage Isolates

2018 ◽  
Vol 200 (16) ◽  
Author(s):  
Bente Børud ◽  
Guro K. Bårnes ◽  
Ola Brønstad Brynildsrud ◽  
Elisabeth Fritzsønn ◽  
Dominique A. Caugant
Keyword(s):  
Neisseria Meningitidis ◽  
Phase Variation ◽  
Protein Glycosylation ◽  
Phase Variable ◽  
Upper Respiratory Tract ◽  
Content Type ◽  
Variable Expression ◽  
Evolutionary Forces ◽  
Strain Collection

ABSTRACTSpecies within the genusNeisseriadisplay significant glycan diversity associated with theO-linked protein glycosylation (pgl) systems due to phase variation and polymorphic genes and gene content. The aim of this study was to examine in detail thepglgenotype and glycosylation phenotype in meningococcal isolates and the changes occurring during short-term asymptomatic carriage. Paired meningococcal isolates derived from 50 asymptomatic meningococcal carriers, taken about 2 months apart, were analyzed with whole-genome sequencing. TheO-linked protein glycosylation genes were characterized in detail using the Genome Comparator tool at the https://pubmlst.org/ database. Immunoblotting with glycan-specific antibodies (Abs) was used to investigate the protein glycosylation phenotype. All majorpgllocus polymorphisms identified inNeisseria meningitidisto date were present in our isolate collection, with the variable presence ofpglGandpglH, both in combination with eitherpglBorpglB2. We identified significant changes and diversity in thepglgenotype and/or glycan phenotype in 96% of the paired isolates. There was also a high degree of glycan microheterogeneity, in which different variants of glycan structures were found at a given glycoprotein. The main mechanism responsible for the observed differences was phase-variable expression of the involved glycosyltransferases and theO-acetyltransferase. To our knowledge, this is the first characterization of thepglgenotype and glycosylation phenotype in a larger strain collection. This report thus provides important insight into glycan diversity inN. meningitidisand into the phase variability changes that influence the expressed glycoform repertoire during meningococcal carriage.IMPORTANCEBacterial meningitis is a serious global health problem, and one of the major causative organisms isNeisseria meningitidis, which is also a common commensal in the upper respiratory tract of healthy humans. In bacteria, numerous loci involved in biosynthesis of surface-exposed antigenic structures that are involved in the interaction between bacteria and host are frequently subjected to homologous recombination and phase variation. These mechanisms are well described inNeisseria, and phase variation provides the ability to change these structures reversibly in response to the environment. Protein glycosylation systems are becoming widely identified in bacteria, and yet little is known about the mechanisms and evolutionary forces influencing glycan composition during carriage and disease.

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