Bacterial Second Messenger Cyclic di-AMP Modulates the Competence State in Streptococcus pneumoniae

ABSTRACT Streptococcus pneumoniae (the pneumococcus) is a naturally competent organism that causes diseases such as pneumonia, otitis media, and bacteremia. The essential bacterial second messenger cyclic di-AMP (c-di-AMP) is an emerging player in the stress responses of many pathogens. In S. pneumoniae, c-di-AMP is produced by a diadenylate cyclase, CdaA, and cleaved by phosphodiesterases Pde1 and Pde2. c-di-AMP binds a transporter of K+ (Trk) family protein, CabP, which subsequently halts K+ uptake via the transporter TrkH. Recently, it was reported that Pde1 and Pde2 are essential for pneumococcal virulence in mouse models of disease. To elucidate c-di-AMP-mediated transcription that may lead to changes in pathogenesis, we compared the transcriptomes of wild-type (WT) and Δpde1 Δpde2 strains by transcriptome sequencing (RNA-Seq) analysis. Notably, we found that many competence-associated genes are significantly upregulated in the Δpde1 Δpde2 strain compared to the WT. These genes play a role in DNA uptake, recombination, and autolysis. Competence is induced by a quorum-sensing mechanism initiated by the secreted factor competence-stimulating peptide (CSP). Surprisingly, the Δpde1 Δpde2 strain exhibited reduced transformation efficiency compared to WT bacteria, which was c-di-AMP dependent. Transformation efficiency was also directly related to the [K+] in the medium, suggesting a link between c-di-AMP function and the pneumococcal competence state. We found that a strain that possesses a V76G variation in CdaA produced less c-di-AMP and was highly susceptible to CSP. Deletion of cabP and trkH restored the growth of these bacteria in medium with CSP. Overall, our study demonstrates a novel role for c-di-AMP in the competence program of S. pneumoniae. IMPORTANCE Genetic competence in bacteria leads to horizontal gene transfer, which can ultimately affect antibiotic resistance, adaptation to stress conditions, and virulence. While the mechanisms of pneumococcal competence signaling cascades have been well characterized, the molecular mechanism behind competence regulation is not fully understood. The bacterial second messenger c-di-AMP has previously been shown to play a role in bacterial physiology and pathogenesis. In this study, we provide compelling evidence for the interplay between c-di-AMP and the pneumococcal competence state. These findings not only attribute a new biological function to this dinucleotide as a regulator of competence, transformation, and survival under stress conditions in pneumococci but also provide new insights into how pneumococcal competence is modulated.

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A Novel Gene Amplification Causes Upregulation of the PatAB ABC Transporter and Fluoroquinolone Resistance in Streptococcus pneumoniae

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.04858-14 ◽

2015 ◽

Vol 59 (6) ◽

pp. 3098-3108 ◽

Cited By ~ 15

Author(s):

Alison J. Baylay ◽

Alasdair Ivens ◽

Laura J. V. Piddock

Keyword(s):

Antibiotic Resistance ◽

Streptococcus Pneumoniae ◽

Abc Transporter ◽

Stress Responses ◽

Fluorescent Protein ◽

Gene Dosage ◽

Fluoroquinolone Resistance ◽

Reporter System ◽

Content Type ◽

Genomic Duplication

ABSTRACTOverexpression of the ABC transporter genespatAandpatBconfers efflux-mediated fluoroquinolone resistance inStreptococcus pneumoniaeand is also linked to pneumococcal stress responses. Although upregulation ofpatABhas been observed in many laboratory mutants and clinical isolates, the regulatory mechanisms controlling expression of these genes are unknown. In this study, we aimed to identify the cause of high-level constitutive overexpression ofpatABin M184, a multidrug-resistant mutant of S.pneumoniaeR6. Using a whole-genome transformation and sequencing approach, we identified a novel duplication of a 9.2-kb region of the M184 genome which included thepatABgenes. This duplication did not affect growth and was semistable with a low segregation rate. The expression levels ofpatABin M184 were much higher than those that could be fully explained by doubling of the gene dosage alone, and inactivation of the first copy ofpatAhad no effect on multidrug resistance. Using a green fluorescent protein reporter system, increasedpatABexpression was ascribed to transcriptional read-through from a tRNA gene upstream of the second copy ofpatAB. This is the first report of a large genomic duplication causing antibiotic resistance inS. pneumoniaeand also of a genomic duplication causing antibiotic resistance by a promoter switching mechanism.

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Genotoxic, Metabolic, and Oxidative Stresses Regulate the RNA Repair Operon ofSalmonella entericaSerovar Typhimurium

Journal of Bacteriology ◽

10.1128/jb.00476-18 ◽

2018 ◽

Vol 200 (23) ◽

Cited By ~ 5

Author(s):

Jennifer E. Kurasz ◽

Christine E. Hartman ◽

David J. Samuels ◽

Bijoy K. Mohanty ◽

Anquilla Deleveaux ◽

...

Keyword(s):

Nucleic Acid ◽

Stress Responses ◽

Nitrogen Limitation ◽

Selective Advantage ◽

Stress Conditions ◽

Rna Repair ◽

Content Type ◽

E Coli ◽

Oxidative Stresses

ABSTRACTThe σ54regulon inSalmonella entericaserovar Typhimurium includes a predicted RNA repair operon encoding homologs of the metazoan Ro60 protein (Rsr), Y RNAs (YrlBA), RNA ligase (RtcB), and RNA 3′-phosphate cyclase (RtcA). Transcription from σ54-dependent promoters requires that a cognate bacterial enhancer binding protein (bEBP) be activated by a specific environmental or cellular signal; the cognate bEBP for the σ54-dependent promoter of thersr-yrlBA-rtcBAoperon is RtcR. To identify conditions that generate the signal for RtcR activation inS. Typhimurium, transcription of the RNA repair operon was assayed under multiple stress conditions that result in nucleic acid damage. RtcR-dependent transcription was highly induced by the nucleic acid cross-linking agents mitomycin C (MMC) and cisplatin, and this activation was dependent on RecA. Deletion ofrtcRorrtcBresulted in decreased cell viability relative to that of the wild type following treatment with MMC. Oxidative stress from peroxide exposure also induced RtcR-dependent transcription of the operon. Nitrogen limitation resulted in RtcR-independent increased expression of the operon; the effect of nitrogen limitation required NtrC. The adjacent toxin-antitoxin module,dinJ-yafQ, was cotranscribed with the RNA repair operon but was not required for RtcR activation, although YafQ endoribonuclease activated RtcR-dependent transcription. Stress conditions shown to induce expression the RNA repair operon ofEscherichia coli(rtcBA) did not stimulate expression of theS. Typhimurium RNA repair operon. Similarly, MMC did not induce expression of theE. colirtcBAoperon, although when expressed inS. Typhimurium,E. coliRtcR responds effectively to the unknown signal(s) generated there by MMC exposure.IMPORTANCEHomologs of the metazoan RNA repair enzymes RtcB and RtcA occur widely in eubacteria, suggesting a selective advantage. Although the enzymatic activities of the eubacterial RtcB and RtcA have been well characterized, the physiological roles remain largely unresolved. Here we report stress responses that activate expression of the σ54-dependent RNA repair operon (rsr-yrlBA-rtcBA) ofS. Typhimurium and demonstrate that expression of the operon impacts cell survival under MMC-induced stress. Characterization of the requirements for activation of this tightly regulated operon provides clues to the possible functions of operon componentsin vivo, enhancing our understanding of how this human pathogen copes with environmental stressors.

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Coping with an Essential Poison: a Genetic Suppressor Analysis Corroborates a Key Function of c-di-AMP in Controlling Potassium Ion Homeostasis in Gram-Positive Bacteria

Journal of Bacteriology ◽

10.1128/jb.00166-18 ◽

2018 ◽

Vol 200 (12) ◽

Cited By ~ 11

Author(s):

Fabian M. Commichau ◽

Jörg Stülke

Keyword(s):

Streptococcus Pneumoniae ◽

Ion Homeostasis ◽

Second Messenger ◽

Potassium Ion ◽

Complex Media ◽

Content Type ◽

Potassium Homeostasis ◽

Intracellular Potassium ◽

Gram Positive Bacteria ◽

Suppressor Analysis

ABSTRACT Cyclic di-AMP (c-di-AMP) is an important second messenger in bacteria. In most Firmicutes , the molecule is required for growth in complex media but also toxic upon accumulation. In an article on their current study, Zarrella and coworkers present a suppressor analysis of a Streptococcus pneumoniae strain that is unable to degrade c-di-AMP (T. M. Zarrella, D. W. Metzger, and G. Bai, J Bacteriol 200:e00045-18, 2018, https://doi.org/10.1128/JB.00045-18 ). Their study identifies new links between c-di-AMP and potassium homeostasis and supports the hypothesis that c-di-AMP serves as a second messenger to report about the intracellular potassium concentrations.

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Stress Survival Islet 2, Predominantly Present in Listeria monocytogenes Strains of Sequence Type 121, Is Involved in the Alkaline and Oxidative Stress Responses

Applied and Environmental Microbiology ◽

10.1128/aem.00827-17 ◽

2017 ◽

Vol 83 (16) ◽

Cited By ~ 34

Author(s):

Eva Harter ◽

Eva Maria Wagner ◽

Andreas Zaiser ◽

Sabrina Halecker ◽

Martin Wagner ◽

...

Keyword(s):

Oxidative Stress ◽

Listeria Monocytogenes ◽

Stress Responses ◽

Food Processing ◽

Stress Conditions ◽

Content Type ◽

Oxidative Stresses ◽

Stress Survival ◽

Oxidative Stress Responses ◽

And Oxidative Stress

ABSTRACT The foodborne pathogen Listeria monocytogenes is able to survive a variety of stress conditions leading to the colonization of different niches like the food processing environment. This study focuses on the hypervariable genetic hot spot lmo0443 to lmo0449 haboring three inserts: the stress survival islet 1 (SSI-1), the single-gene insert LMOf2365_0481, and two homologous genes of the nonpathogenic species Listeria innocua: lin0464, coding for a putative transcriptional regulator, and lin0465, encoding an intracellular PfpI protease. Our prevalence study revealed a different distribution of the inserts between human and food-associated isolates. The lin0464-lin0465 insert was predominantly found in food-associated strains of sequence type 121 (ST121). Functional characterization of this insert showed that the putative PfpI protease Lin0465 is involved in alkaline and oxidative stress responses but not in acidic, gastric, heat, cold, osmotic, and antibiotic stresses. In parallel, deletion of lin0464 decreased survival under alkaline and oxidative stresses. The expression of both genes increased significantly under oxidative stress conditions independently of the alternative sigma factor σB. Furthermore, we showed that the expression of the protease gene lin0465 is regulated by the transcription factor lin0464 under stress conditions, suggesting that lin0464 and lin0465 form a functional unit. In conclusion, we identified a novel stress survival islet 2 (SSI-2), predominantly present in L. monocytogenes ST121 strains, beneficial for survival under alkaline and oxidative stresses, potentially supporting adaptation and persistence of L. monocytogenes in food processing environments. IMPORTANCE Listeria monocytogenes strains of ST121 are known to persist for months and even years in food processing environments, thereby increasing the risk of food contamination and listeriosis. However, the molecular mechanism underlying this remarkable niche-specific adaptation is still unknown. Here, we demonstrate that the genomic islet SSI-2, predominantly present in L. monocytogenes ST121 strains, is beneficial for survival under alkaline and oxidative stress conditions, which are routinely encountered in food processing environments. Our findings suggest that SSI-2 is part of a diverse set of molecular determinants contributing to niche-specific adaptation and persistence of L. monocytogenes ST121 strains in food processing environments.

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Functional Characterization of Crp/Fnr-Type Global Transcriptional Regulators in Desulfovibrio vulgaris Hildenborough

Applied and Environmental Microbiology ◽

10.1128/aem.05666-11 ◽

2011 ◽

Vol 78 (4) ◽

pp. 1168-1177 ◽

Cited By ~ 19

Author(s):

Aifen Zhou ◽

Yunyu I. Chen ◽

Grant M. Zane ◽

Zhili He ◽

Christopher L. Hemme ◽

...

Keyword(s):

Stress Responses ◽

Environmental Changes ◽

Transcriptional Profiling ◽

Functional Characterization ◽

Reduction Rate ◽

Detrended Correspondence Analysis ◽

Transcriptional Regulators ◽

Stress Conditions ◽

Desulfovibrio Vulgaris ◽

Content Type

ABSTRACTCrp/Fnr-type global transcriptional regulators regulate various metabolic pathways in bacteria and typically function in response to environmental changes. However, little is known about the function of four annotated Crp/Fnr homologs (DVU0379, DVU2097, DVU2547, and DVU3111) inDesulfovibrio vulgarisHildenborough. A systematic study using bioinformatic, transcriptomic, genetic, and physiological approaches was conducted to characterize their roles in stress responses. Similar growth phenotypes were observed for thecrp/fnrdeletion mutants under multiple stress conditions. Nevertheless, the idea of distinct functions of Crp/Fnr-type regulators in stress responses was supported by phylogeny, gene transcription changes, fitness changes, and physiological differences. The fourD. vulgarisCrp/Fnr homologs are localized in three subfamilies (HcpR, CooA, andcc). Thecrp/fnrknockout mutants were well separated by transcriptional profiling using detrended correspondence analysis (DCA), and more genes significantly changed in expression in a ΔDVU3111 mutant (JW9013) than in the other three paralogs. In fitness studies, strain JW9013 showed the lowest fitness under standard growth conditions (i.e., sulfate reduction) and the highest fitness under NaCl or chromate stress conditions; better fitness was observed for a ΔDVU2547 mutant (JW9011) under nitrite stress conditions and a ΔDVU2097 mutant (JW9009) under air stress conditions. A higher Cr(VI) reduction rate was observed for strain JW9013 in experiments with washed cells. These results suggested that the four Crp/Fnr-type global regulators play distinct roles in stress responses ofD. vulgaris. DVU3111 is implicated in responses to NaCl and chromate stresses, DVU2547 in nitrite stress responses, and DVU2097 in air stress responses.

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A Novel Phosphodiesterase of the GdpP Family Modulates Cyclic di-AMP Levels in Response to Cell Membrane Stress in Daptomycin-Resistant Enterococci

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01422-16 ◽

2017 ◽

Vol 61 (3) ◽

Cited By ~ 11

Author(s):

Xu Wang ◽

Milya Davlieva ◽

Jinnethe Reyes ◽

Diana Panesso ◽

Cesar A. Arias ◽

...

Keyword(s):

Cell Membrane ◽

Stress Responses ◽

Specific Activity ◽

Response Regulator ◽

Physicochemical Characterization ◽

Membrane Stress ◽

Signal Molecule ◽

Content Type ◽

Bacterial Physiology

ABSTRACT Substitutions in the LiaFSR membrane stress pathway are frequently associated with the emergence of antimicrobial peptide resistance in both Enterococcus faecalis and Enterococcus faecium. Cyclic di-AMP (c-di-AMP) is an important signal molecule that affects many aspects of bacterial physiology, including stress responses. We have previously identified a mutation in a gene (designated yybT) in E. faecalis that was associated with the development of daptomycin resistance, resulting in a change at position 440 (yybT I440S) in the predicted protein. Here, we show that intracellular c-di-AMP signaling is present in enterococci, and on the basis of in vitro physicochemical characterization, we show that E. faecalis yybT encodes a cyclic dinucleotide phosphodiesterase of the GdpP family that exhibits specific activity toward c-di-AMP by hydrolyzing it to 5′pApA. The E. faecalis GdpPI440S substitution reduces c-di-AMP phosphodiesterase activity more than 11-fold, leading to further increases in c-di-AMP levels. Additionally, deletions of liaR (encoding the response regulator of the LiaFSR system) that lead to daptomycin hypersusceptibility in both E. faecalis and E. faecium also resulted in increased c-di-AMP levels, suggesting that changes in the LiaFSR stress response pathway are linked to broader physiological changes. Taken together, our data show that modulation of c-di-AMP pools is strongly associated with antibiotic-induced cell membrane stress responses via changes in GdpP activity or signaling through the LiaFSR system.

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Global Transcriptional Analysis of clpP Mutations of Type 2 Streptococcus pneumoniae and Their Effects on Physiology and Virulence

Journal of Bacteriology ◽

10.1128/jb.184.13.3508-3520.2002 ◽

2002 ◽

Vol 184 (13) ◽

pp. 3508-3520 ◽

Cited By ~ 99

Author(s):

Gregory T. Robertson ◽

Wai-Leung Ng ◽

Joseph Foley ◽

Raymond Gilmour ◽

Malcolm E. Winkler

Keyword(s):

Oxidative Stress ◽

Streptococcus Pneumoniae ◽

Heat Shock ◽

Microarray Analysis ◽

Stress Responses ◽

Metal Ion ◽

Transcriptional Analysis ◽

Exponential Growth Phase ◽

Dna Uptake

ABSTRACT Streptococcus pneumoniae is an important human pathogen that contains single copies of genes encoding the ClpP and FtsH ATP-dependent proteases but lacks the Lon and HslV proteases. We constructed and characterized the phenotypes of clpP, clpC, and clpX deletion replacement mutants, which lack the ClpP protease subunit or the putative ClpC or ClpX ATPase specificity factor. A ΔclpP mutant, but not a ΔclpC or ΔclpX mutant, of the virulent D39 type 2 strain of S. pneumoniae grew poorly at 30°C and failed to grow at 40°C. Despite this temperature sensitivity, transcription of the heat shock regulon determined by microarray analysis was induced in a ΔclpP mutant, which was also more sensitive to oxidative stress by H2O2 and to puromycin than its clpP + parent strain. A ΔclpP mutant, but not a ΔclpC mutant, was strongly attenuated for virulence in the murine lung and sepsis infection models. All of these phenotypes were complemented in a ΔclpP/clpP + merodiploid strain. Consistent with these complementation patterns, clpP was found to be in a monocistronic operon, whose transcription was induced about fivefold by heat shock in S. pneumoniae as determined by Northern and real-time reverse transcription-PCR analyses. Besides clpP, transcription of clpC, clpE, and clpL, but not clpX or ftsH, was induced by heat shock or entry into late exponential growth phase. Microarray analysis of ΔclpP mutants showed a limited change in transcription pattern (≈80 genes) consistent with these phenotypes, including repression of genes involved in oxidative stress, metal ion transport, and virulence. In addition, transcription of the early and late competence regulon was induced in the ΔclpP mutant, and competence gene expression and DNA uptake seemed to be constitutively induced throughout growth. Together, these results indicate that ClpP-mediated proteolysis plays a complex and central role in numerous pneumococcal stress responses, development of competence, and virulence.

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c-di-AMP Accumulation Impairs Muropeptide Synthesis in Listeria monocytogenes

Journal of Bacteriology ◽

10.1128/jb.00307-20 ◽

2020 ◽

Vol 202 (24) ◽

Author(s):

Steven M. Massa ◽

Amar Deep Sharma ◽

Cheta Siletti ◽

Zepeng Tu ◽

Jared J. Godfrey ◽

...

Keyword(s):

Cell Wall ◽

Listeria Monocytogenes ◽

Cell Envelope ◽

Second Messenger ◽

Fold Increase ◽

Bacterial Cells ◽

Content Type ◽

Bacterial Physiology ◽

Peptidoglycan Synthesis ◽

Increased Sensitivity

ABSTRACT Cyclic di-AMP (c-di-AMP) is an essential and ubiquitous second messenger among bacteria. c-di-AMP regulates many cellular pathways through direct binding to several molecular targets in bacterial cells. c-di-AMP depletion is well known to destabilize the bacterial cell wall, resulting in increased bacteriolysis and enhanced susceptibility to cell wall targeting antibiotics. Using the human pathogen Listeria monocytogenes as a model, we found that c-di-AMP accumulation also impaired cell envelope integrity. An L. monocytogenes mutant deleted for c-di-AMP phosphodiesterases (pdeA pgpH mutant) exhibited a 4-fold increase in c-di-AMP levels and several cell wall defects. For instance, the pdeA pgpH mutant was defective for the synthesis of peptidoglycan muropeptides and was susceptible to cell wall-targeting antimicrobials. Among different muropeptide precursors, we found that the pdeA pgpH strain was particularly impaired in the synthesis of d-Ala–d-Ala, which is required to complete the pentapeptide stem associated with UDP–N-acetylmuramic acid (MurNAc). This was consistent with an increased sensitivity to d-cycloserine, which inhibits the d-alanine branch of peptidoglycan synthesis. Finally, upon examining d-Ala:d-Ala ligase (Ddl), which catalyzes the conversion of d-Ala to d-Ala–d-Ala, we found that its activity was activated by K+. Based on previous reports that c-di-AMP inhibits K+ uptake, we propose that c-di-AMP accumulation impairs peptidoglycan synthesis, partially through the deprivation of cytoplasmic K+ levels, which are required for cell wall-synthetic enzymes. IMPORTANCE The bacterial second messenger c-di-AMP is produced by a large number of bacteria and conditionally essential to many species. Conversely, c-di-AMP accumulation is also toxic to bacterial physiology and pathogenesis, but its mechanisms are largely undefined. We found that in Listeria monocytogenes, elevated c-di-AMP levels diminished muropeptide synthesis and increased susceptibility to cell wall-targeting antimicrobials. Cell wall defects might be an important mechanism for attenuated virulence in bacteria with high c-di-AMP levels.

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Differences in Antibiotic-Induced Oxidative Stress Responses between Laboratory and Clinical Isolates of Streptococcus pneumoniae

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00316-15 ◽

2015 ◽

Vol 59 (9) ◽

pp. 5420-5426 ◽

Cited By ~ 13

Author(s):

Bédis Dridi ◽

Andréanne Lupien ◽

Michel G. Bergeron ◽

Philippe Leprohon ◽

Marc Ouellette

Keyword(s):

Oxidative Stress ◽

Reactive Oxygen Species ◽

Streptococcus Pneumoniae ◽

Stress Responses ◽

Bacterial Species ◽

Reactive Oxygen ◽

Clinical Isolates ◽

Complex Nature ◽

Oxygen Species ◽

Content Type

ABSTRACTOxidants were shown to contribute to the lethality of bactericidal antibiotics in different bacterial species, including the laboratory strainStreptococcus pneumoniaeR6. Resistance to penicillin amongS. pneumoniaeR6 mutants was further shown to protect against the induction of oxidants upon exposure to unrelated bactericidal compounds. In the work described here, we expanded on these results by studying the accumulation of reactive oxygen species in the context of antibiotic sensitivity and resistance by includingS. pneumoniaeclinical isolates. InS. pneumoniaeR6, penicillin, ciprofloxacin, and kanamycin but not the bacteriostatic linezolid, erythromycin, or tetracycline induced the accumulation of reactive oxygen species. For the three bactericidal compounds, resistance to a single molecule prevented the accumulation of oxidants upon exposure to unrelated bactericidal antibiotics, and this was accompanied by a reduced lethality. This phenomenon does not involve target site mutations but most likely implicates additional mutations occurring early during the selection of resistance to increase survival while more efficient resistance mechanisms are being selected or acquired. Bactericidal antibiotics also induced oxidants in sensitiveS. pneumoniaeclinical isolates. The importance of oxidants in the lethality of bactericidal antibiotics was less clear than forS. pneumoniaeR6, however, since ciprofloxacin induced oxidants even in ciprofloxacin-resistantS. pneumoniaeclinical isolates. Our results provide a clear example of the complex nature of the mode of action of antibiotics. The adaptive approach to oxidative stress ofS. pneumoniaeis peculiar, and a better understanding of the mechanism implicated in response to oxidative injury should also help clarify the role of oxidants induced by antibiotics.

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Antibodies to Streptococcus pneumoniae Capsular Polysaccharide Enhance Pneumococcal Quorum Sensing

mBio ◽

10.1128/mbio.00176-11 ◽

2011 ◽

Vol 2 (5) ◽

Cited By ~ 22

Author(s):

Masahide Yano ◽

Shruti Gohil ◽

J. Robert Coleman ◽

Catherine Manix ◽

Liise-anne Pirofski

Keyword(s):

Monoclonal Antibodies ◽

Streptococcus Pneumoniae ◽

Quorum Sensing ◽

Direct Effect ◽

Pneumococcal Disease ◽

Effector Cell ◽

Capsular Polysaccharide ◽

Genetic Exchange ◽

Content Type ◽

Specific Antibodies

ABSTRACTThe use of pneumococcal capsular polysaccharide (PPS)-based vaccines has resulted in a substantial reduction in invasive pneumococcal disease. However, much remains to be learned about vaccine-mediated immunity, as seven-valent PPS-protein conjugate vaccine use in children has been associated with nonvaccine serotype replacement and 23-valent vaccine use in adults has not prevented pneumococcal pneumonia. In this report, we demonstrate that certain PPS-specific monoclonal antibodies (MAbs) enhance the transformation frequency of two differentStreptococcus pneumoniaeserotypes. This phenomenon was mediated by PPS-specific MAbs that agglutinate but do not promote opsonic effector cell killing of the homologous serotypeinvitro. Compared to the autoinducer, competence-stimulating peptide (CSP) alone, transcriptional profiling of pneumococcal gene expression after incubation with CSP and one such MAb to the PPS of serotype 3 revealed changes in the expression of competence (com)-related and bacteriocin-like peptide (blp) genes involved in pneumococcal quorum sensing. This MAb was also found to induce a nearly 2-fold increase in CSP2-mediated bacterial killing or fratricide. These observations reveal a novel, direct effect of PPS-binding MAbs on pneumococcal biology that has important implications for antibody immunity to pneumococcus in the pneumococcal vaccine era. Taken together, our data suggest heretofore unsuspected mechanisms by which PPS-specific antibodies could affect genetic exchange and bacterial viability in the absence of host cells.IMPORTANCECurrent thought holds that pneumococcal capsular polysaccharide (PPS)-binding antibodies protect against pneumococcus by inducing effector cell opsonic killing of the homologous serotype. While such antibodies are an important part of how pneumococcal vaccines protect against pneumococcal disease, PPS-specific antibodies that do not exhibit this activity but are highly protective against pneumococcus in mice have been identified. This article examines the effect of nonopsonic PPS-specific monoclonal antibodies (MAbs) on the biology ofStreptococcus pneumoniae. The results showed that in the presence of a competence-stimulating peptide (CSP), such MAbs increase the frequency of pneumococcal transformation. Further studies with one such MAb showed that it altered the expression of genes involved in quorum sensing and increased competence-induced killing or fratricide. These findings reveal a novel, previously unsuspected mechanism by which certain PPS-specific antibodies exert a direct effect on pneumococcal biology that has broad implications for bacterial clearance, genetic exchange, and antibody immunity to pneumococcus.

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