scholarly journals The Sortase SrtA of Listeria monocytogenes Is Involved in Processing of Internalin and in Virulence

2002 ◽  
Vol 70 (3) ◽  
pp. 1382-1390 ◽  
Author(s):  
Caroline Garandeau ◽  
Hélène Réglier-Poupet ◽  
Iharilalao Dubail ◽  
Jean-Luc Beretti ◽  
Patrick Berche ◽  
...  
Keyword(s):  
Cell Wall ◽  
Listeria Monocytogenes ◽  
Protein A ◽  
Knockout Mutant ◽  
Reporter Protein ◽  
Gram Positive ◽  
Bacterial Surface ◽  
Gram Positive Bacteria ◽  
Covalently Linked

ABSTRACT Listeria monocytogenes is an intracellular gram-positive human pathogen that invades eucaryotic cells. Among the surface-exposed proteins playing a role in this invasive process, internalin belongs to the family of LPXTG proteins, which are known to be covalently linked to the bacterial cell wall in gram-positive bacteria. Recently, it has been shown in Staphylococcus aureus that the covalent anchoring of protein A, a typical LPXTG protein, is due to a cysteine protease, named sortase, required for bacterial virulence. Here, we identified in silico from the genome of L. monocytogenes a gene, designated srtA, encoding a sortase homologue. The role of this previously unknown sortase was studied by constructing a sortase knockout mutant. Internalin was used as a reporter protein to study the effects of the srtA mutation on cell wall anchoring of this LPXTG protein in L. monocytogenes. We show that the srtA mutant (i) is affected in the display of internalin at the bacterial surface, (ii) is significantly less invasive in vitro, and (iii) is attenuated in its virulence in the mouse. These results demonstrate that srtA of L. monocytogenes acts as a sortase and plays a role in the pathogenicity.

scholarly journals Inactivation of the srtA Gene inStreptococcus gordonii Inhibits Cell Wall Anchoring of Surface Proteins and Decreases In Vitro and In Vivo Adhesion

2001 ◽  
Vol 69 (1) ◽  
pp. 75-80 ◽  
Author(s):  
Tové C. Bolken ◽  
Christine A. Franke ◽  
Kevin F. Jones ◽  
Gloria O. Zeller ◽  
C. Hal Jones ◽  
...  
Keyword(s):  
Cell Wall ◽  
Protein A ◽  
Surface Protein ◽  
Surface Proteins ◽  
Gram Positive ◽  
Gram Positive Bacteria ◽  
Human Fibronectin ◽  
Gram Positive Cocci

ABSTRACT The srtA gene product, SrtA, has been shown to be required for cell wall anchoring of protein A as well as virulence in the pathogenic bacterium Staphylococcus aureus. There are five major mechanisms for displaying proteins at the surface of gram-positive bacteria (P. Cossart and R. Jonquieres, Proc. Natl. Acad. Sci. USA 97:5013–5015, 2000). However, since many of the known surface proteins of gram-positive bacteria are believed to be exported and anchored via the sortase pathway, it was of interest to determine ifsrtA plays a similar role in other gram-positive bacteria. To that end, the srtA gene in the human oral commensal organism Streptococcus gordonii was insertionally inactivated. The srtA mutant S. gordoniiexhibited a marked reduction in quantity of a specific anchored surface protein. Furthermore, the srtA mutant had reduced binding to immobilized human fibronectin and had a decreased ability to colonize the oral mucosa of mice. Taken together, these results suggest that the activity of SrtA plays an important role in the biology of nonpathogenic as well as pathogenic gram-positive cocci.

scholarly journals Mutations of the Listeria monocytogenes PeptidoglycanN-Deacetylase andO-Acetylase Result in Enhanced Lysozyme Sensitivity, Bacteriolysis, and Hyperinduction of Innate Immune Pathways

2011 ◽  
Vol 79 (9) ◽  
pp. 3596-3606 ◽  
Author(s):  
Chris S. Rae ◽  
Aimee Geissler ◽  
Paul C. Adamson ◽  
Daniel A. Portnoy
Keyword(s):  
Listeria Monocytogenes ◽  
Transcriptional Responses ◽  
Gram Positive ◽  
Content Type ◽  
Growth Defects ◽  
Gram Positive Bacteria ◽  
Host Cell Death

ABSTRACTListeria monocytogenesis a Gram-positive intracellular pathogen that is naturally resistant to lysozyme. Recently, it was shown that peptidoglycan modification by N-deacetylation or O-acetylation confers resistance to lysozyme in various Gram-positive bacteria, includingL. monocytogenes.L. monocytogenespeptidoglycan is deacetylated by the action ofN-acetylglucosamine deacetylase (Pgd) and acetylated byO-acetylmuramic acid transferase (Oat). We characterized Pgd−, Oat−, and double mutants to determine the specific role ofL. monocytogenespeptidoglycan acetylation in conferring lysozyme sensitivity during infection of macrophages and mice. Pgd−and Pgd−Oat−double mutants were attenuated approximately 2 and 3.5 logs, respectively,in vivo. In bone-marrow derived macrophages, the mutants demonstrated intracellular growth defects and increased induction of cytokine transcriptional responses that emanated from a phagosome and the cytosol. Lysozyme-sensitive mutants underwent bacteriolysis in the macrophage cytosol, resulting in AIM2-dependent pyroptosis. Each of thein vitrophenotypes was rescued upon infection of LysM−macrophages. The addition of extracellular lysozyme to LysM−macrophages restored cytokine induction, host cell death, andL. monocytogenesgrowth inhibition. This surprising observation suggests that extracellular lysozyme can access the macrophage cytosol and act on intracellular lysozyme-sensitive bacteria.

scholarly journals Another Brick in the Wall: a Rhamnan Polysaccharide Trapped inside Peptidoglycan of Lactococcus lactis

mBio ◽  
2017 ◽  
Vol 8 (5) ◽  
Author(s):  
Irina Sadovskaya ◽  
Evgeny Vinogradov ◽  
Pascal Courtin ◽  
Julija Armalyte ◽  
Mickael Meyrand ◽  
...  
Keyword(s):  
Cell Wall ◽  
Lactococcus Lactis ◽  
Abc Transporter ◽  
Present Report ◽  
Gram Positive ◽  
Narrow Host Range ◽  
Bacterial Surface ◽  
Gram Positive Bacteria ◽  
Major Structural Component ◽  
Dependent Pathway

ABSTRACT Polysaccharides are ubiquitous components of the Gram-positive bacterial cell wall. In Lactococcus lactis, a polysaccharide pellicle (PSP) forms a layer at the cell surface. The PSP structure varies among lactococcal strains; in L. lactis MG1363, the PSP is composed of repeating hexasaccharide phosphate units. Here, we report the presence of an additional neutral polysaccharide in L. lactis MG1363 that is a rhamnan composed of α-l-Rha trisaccharide repeating units. This rhamnan is still present in mutants devoid of the PSP, indicating that its synthesis can occur independently of PSP synthesis. High-resolution magic-angle spinning nuclear magnetic resonance (HR-MAS NMR) analysis of whole bacterial cells identified a PSP at the surface of wild-type cells. In contrast, rhamnan was detected only at the surface of PSP-negative mutant cells, indicating that rhamnan is located underneath the surface-exposed PSP and is trapped inside peptidoglycan. The genetic determinants of rhamnan biosynthesis appear to be within the same genetic locus that encodes the PSP biosynthetic machinery, except the gene tagO encoding the initiating glycosyltransferase. We present a model of rhamnan biosynthesis based on an ABC transporter-dependent pathway. Conditional mutants producing reduced amounts of rhamnan exhibit strong morphological defects and impaired division, indicating that rhamnan is essential for normal growth and division. Finally, a mutation leading to reduced expression of lcpA, encoding a protein of the LytR-CpsA-Psr (LCP) family, was shown to severely affect cell wall structure. In lcpA mutant cells, in contrast to wild-type cells, rhamnan was detected by HR-MAS NMR, suggesting that LcpA participates in the attachment of rhamnan to peptidoglycan. IMPORTANCE In the cell wall of Gram-positive bacteria, the peptidoglycan sacculus is considered the major structural component, maintaining cell shape and integrity. It is decorated with other glycopolymers, including polysaccharides, the roles of which are not fully elucidated. In the ovococcus Lactococcus lactis, a polysaccharide with a different structure between strains forms a layer at the bacterial surface and acts as the receptor for various bacteriophages that typically exhibit a narrow host range. The present report describes the identification of a novel polysaccharide in the L. lactis cell wall, a rhamnan that is trapped inside the peptidoglycan and covalently bound to it. We propose a model of rhamnan synthesis based on an ABC transporter-dependent pathway. Rhamnan appears as a conserved component of the lactococcal cell wall playing an essential role in growth and division, thus highlighting the importance of polysaccharides in the cell wall integrity of Gram-positive ovococci. IMPORTANCE In the cell wall of Gram-positive bacteria, the peptidoglycan sacculus is considered the major structural component, maintaining cell shape and integrity. It is decorated with other glycopolymers, including polysaccharides, the roles of which are not fully elucidated. In the ovococcus Lactococcus lactis, a polysaccharide with a different structure between strains forms a layer at the bacterial surface and acts as the receptor for various bacteriophages that typically exhibit a narrow host range. The present report describes the identification of a novel polysaccharide in the L. lactis cell wall, a rhamnan that is trapped inside the peptidoglycan and covalently bound to it. We propose a model of rhamnan synthesis based on an ABC transporter-dependent pathway. Rhamnan appears as a conserved component of the lactococcal cell wall playing an essential role in growth and division, thus highlighting the importance of polysaccharides in the cell wall integrity of Gram-positive ovococci.

Behavior of Listeria monocytogenes and Staphylococcus aureus in Yogurt Fermented with a Bacteriocin-Producing Thermophilic Starter

2002 ◽  
Vol 65 (5) ◽  
pp. 799-805 ◽  
Author(s):  
NOREDDINE BENKERROUM ◽  
HAFIDA OUBEL ◽  
LAMIAE BEN MIMOUN
Keyword(s):  
Staphylococcus Aureus ◽  
Listeria Monocytogenes ◽  
Lactobacillus Delbrueckii ◽  
Gram Positive ◽  
Gram Positive Bacteria ◽  
Bakery Yeast ◽  
Adsorption Desorption ◽  
And Staphylococcus Aureus

Streptococcus salivarius subsp. thermophilus B producing a bacteriocin active against Listeria monocytogenes ATCC 7644 and Staphylococcus aureus SAD 30 was isolated from bakery yeast. The bacteriocin was partially purified by an adsorption/desorption technique, and its spectrum of action was compared to that of a neutralized cell-free supernatant (CFS). Although the CFS inhibited a number of gram-positive and -negative bacteria of health and spoilage significance, the spectrum of action of the partially purified bacteriocin was limited to gram-positive bacteria. L. monocytogenes was the most sensitive to both preparations. The bacteriocin-producing streptococcal strain was used in combination with a Bac− Lactobacillus delbrueckii subsp. bulgaricus CY strain isolated from commercial yogurt to assess the effectiveness of the resulting thermophilic starter in controlling L. monocytogenes and S. aureus in yogurt during fermentation and storage at refrigeration (ca. 7°C) or abuse (ca. 22°C) temperature. Yogurt samples were contaminated with L. monocytogenes or S. aureus to the approximate levels of 103 and 106 CFU/ml of milk, respectively. The results showed that in situ bacteriocin production was more active against L. monocytogenes than against S. aureus in vitro and in contaminated samples. While L. monocytogenes leveled off below the detectable limit in a 1-ml sample of yogurt within 24 h of processing, S. aureus survived in Bac+ and Bac− samples during 10 days of storage at room temperature (ca. 22°C). Use of a Bac+ starter resulted in a 5-day extension of the shelf life.

scholarly journals AsnB Mediates Amidation of Meso-Diaminopimelic Acid Residues in the Peptidoglycan of Listeria monocytogenes and Affects Bacterial Surface Properties and Host Cell Invasion

2021 ◽  
Vol 12 ◽  
Author(s):  
Lei Sun ◽  
Gil Rogiers ◽  
Pascal Courtin ◽  
Marie-Pierre Chapot-Chartier ◽  
Hélène Bierne ◽  
...  
Keyword(s):  
Cell Wall ◽  
Listeria Monocytogenes ◽  
Cell Surface ◽  
Bacterial Species ◽  
Functional Characterization ◽  
Diaminopimelic Acid ◽  
Bacterial Surface ◽  
Gram Positive Bacteria ◽  
First Time

A mutant of Listeria monocytogenes ScottA with a transposon in the 5' untranslated region of the asnB gene was identified to be hypersensitive to the antimicrobial t-cinnamaldehyde. Here, we report the functional characterization of AsnB in peptidoglycan (PG) modification and intracellular infection. While AsnB of Listeria is annotated as a glutamine-dependent asparagine synthase, sequence alignment showed that this protein is closely related to a subset of homologs that catalyze the amidation of meso-diaminopimelic acid (mDAP) residues in the peptidoglycan of other bacterial species. Structural analysis of peptidoglycan from an asnB mutant, compared to that of isogenic wild-type (WT) and complemented mutant strains, confirmed that AsnB mediates mDAP amidation in L. monocytogenes. Deficiency in mDAP amidation caused several peptidoglycan- and cell surface-related phenotypes in the asnB mutant, including formation of shorter but thicker cells, susceptibility to lysozyme, loss of flagellation and motility, and a strong reduction in biofilm formation. In addition, the mutant showed reduced invasion of human epithelial JEG-3 and Caco-2 cells. Analysis by immunofluorescence microscopy revealed that asnB inactivation abrogated the proper display at the listerial surface of the invasion protein InlA, which normally gets cross-linked to mDAP via its LPXTG motif. Together, this work shows that AsnB of L. monocytogenes, like several of its homologs in related Gram-positive bacteria, mediates the amidation of mDAP residues in the peptidoglycan and, in this way, affects several cell wall and cell surface-related properties. It also for the first time implicates the amidation of peptidoglycan mDAP residues in cell wall anchoring of InlA and in bacterial virulence.

scholarly journals Characteristics of Surfactant Protein A and D Binding to Lipoteichoic Acid and Peptidoglycan, 2 Major Cell Wall Components of Gram‐Positive Bacteria

2001 ◽  
Vol 184 (9) ◽  
pp. 1143-1151 ◽  
Author(s):  
J. Koenraad van de Wetering ◽  
Martin van Eijk ◽  
Lambert M. G. van Golde ◽  
Thomas Hartung ◽  
Jos A. G. van Strijp ◽  
...  
Keyword(s):  
Cell Wall ◽  
Protein A ◽  
Lipoteichoic Acid ◽  
Surfactant Protein ◽  
Surfactant Protein A ◽  
Gram Positive ◽  
Cell Wall Components ◽  
Gram Positive Bacteria ◽  
Wall Components

scholarly journals Characterization of Streptococcus suis Genes Encoding Proteins Homologous to Sortase of Gram-Positive Bacteria

2002 ◽  
Vol 184 (4) ◽  
pp. 971-982 ◽  
Author(s):  
Makoto Osaki ◽  
Daisuke Takamatsu ◽  
Yoshihiro Shimoji ◽  
Tsutomu Sekizaki
Keyword(s):  
Cell Wall ◽  
Streptococcus Suis ◽  
Amino Acid Sequences ◽  
Surface Proteins ◽  
Gram Positive ◽  
Two Dimensional Gel Electrophoresis ◽  
Gram Positive Bacteria ◽  
Genes Encoding ◽  
Covalently Linked ◽  
Sorting System

ABSTRACT Many surface proteins which are covalently linked to the cell wall of gram-positive bacteria have a consensus C-terminal motif, Leu-Pro-X-Thr-Gly (LPXTG). This sequence is cleaved, and the processed protein is attached to an amino group of a cross-bridge in the peptideglycan by a specific enzyme called sortase. Using the type strain of Streptococcus suis, NCTC 10234, we found five genes encoding proteins that were homologous to sortases of other bacteria and determined the nucleotide sequences of the genetic regions. One gene, designated srtA, was linked to gyrA, as were the sortase and sortase-like genes of other streptococci. Three genes, designated srtB, srtC, and srtD, were tandemly clustered in a different location, where there were three segments of directly repeated sequences of approximately 110 bp in close vicinity. The remaining gene, designated srtE, was located separately on the chromosome with a pseudogene which may encode a transposase. The deduced amino acid sequences of the five Srt proteins showed 18 to 31% identity with the sortases of Streptococcus gordonii and Staphylococcus aureus, except that SrtA of S. suis had 65% identity with that of S. gordonii. Isogenic mutants deficient for srtA, srtBCD, or srtE were generated by allelic exchanges. The protein fraction which was released from partially purified cell walls by digestion with N-acetylmuramidase was profiled by two-dimensional gel electrophoresis. More than 15 of the protein spots were missing in the profile of the srtA mutant compared with that of the parent strain, and this phenotype was completely complemented by srtA cloned from S. suis. Four genes encoding proteins corresponding to such spots were identified and sequenced. The deduced translational products of the four genes possessed the LPXTG motif in their C-terminal regions. On the other hand, the protein spots that were missing in the srtA mutant appeared in the profiles of the srtBCD and srtE mutants. These results provide evidence that the cell wall sorting system involving srtA is also present in S. suis.

scholarly journals MurA escape mutations uncouple peptidoglycan biosynthesis from PrkA signaling

2021 ◽  
Author(s):  
Sabrina Wamp ◽  
Patricia Rothe ◽  
Gudrun Holland ◽  
Sven Halbedel
Keyword(s):  
Cell Wall ◽  
Listeria Monocytogenes ◽  
Protein Kinase ◽  
Bacterial Cell ◽  
Bacterial Cell Wall ◽  
Escape Mutation ◽  
Gram Positive ◽  
Gram Positive Bacteria ◽  
Main Component ◽  
Biosynthesis Regulation

AbstractGram-positive bacteria are protected by a thick mesh of peptidoglycan (PG) completely engulfing their cells. This PG network is the main component of the bacterial cell wall, it provides rigidity and acts as foundation for the attachment of other surface molecules. Biosynthesis of PG consumes a high amount of cellular resources and therefore requires careful adjustments to environmental conditions.An important switch in the control of PG biosynthesis of Listeria monocytogenes, a Gram-positive pathogen with a high infection fatality rate, is the serine/threonine protein kinase PrkA. A key substrate of this kinase is the small cytosolic protein ReoM. We have shown previously that ReoM phosphorylation regulates PG formation through control of MurA stability. MurA catalyzes the first step in PG biosynthesis and the current model suggests that phosphorylated ReoM prevents MurA degradation by the ClpCP protease. In contrast, conditions leading to ReoM dephosphorylation stimulate MurA degradation. How ReoM controls degradation of MurA and potential other substrates is not understood. Also, the individual contribution of the ∼20 other known PrkA targets to PG biosynthesis regulation is unknown.We here present murA mutants which escape proteolytic degradation. The release of MurA from ClpCP-dependent proteolysis was able to constitutively activate PG biosynthesis and further enhances the intrinsic cephalosporin resistance of L. monocytogenes. This activation required the RodA3/PBP B3 transglycosylase/transpeptidase pair as additional effectors of the PrkA signaling route. One murA escape mutation not only fully rescued an otherwise non-viable prkA mutant during growth in batch culture and inside macrophages but also overcompensated cephalosporin hypersensitivity. Our data collectively indicate that the main purpose of PrkA-mediated signaling in L. monocytogenes is control of MurA stability during extra- and intracellular growth. These findings have important implications for the understanding of PG biosynthesis regulation and β-lactam resistance of L. monocytogenes and related Gram-positive bacteria.Author SummaryPeptidoglycan (PG) is the main component of the bacterial cell wall and many of the PG synthesizing enzymes are antibiotic targets. We previously have discovered a new signaling route controlling PG production in the human pathogen Listeria monocytogenes. This route also determines the intrinsic resistance of L. monocytogenes against cephalosporins, a group of β-lactam antibiotics. Signaling involves PrkA, a membrane-embedded protein kinase, that is activated during cell wall stress to phosphorylate its target ReoM. Depending on its phosphorylation, ReoM activates or inactivates PG production by controlling the proteolytic stability of MurA, which catalyzes the first step in PG biosynthesis. MurA degradation depends on the ClpCP protease and we here have isolated murA mutations that escape this degradation. Using these mutants, we could show that regulation of PG biosynthesis through control of MurA stability is the primary purpose of PrkA-mediated signaling in L. monocytogenes. Further experiments identified the transglycosylase RodA and the transpeptidase PBP B3 as additional effectors of PrkA signaling. Our results suggest that both proteins act together to translate the signals received by PrkA into intensification of PG biosynthesis. These findings shed new light on the regulation of PG biosynthesis in Gram-positive bacteria with intrinsic β-lactam resistance.

scholarly journals C-Terminal WxL Domain Mediates Cell Wall Binding in Enterococcus faecalis and Other Gram-Positive Bacteria

2006 ◽  
Vol 189 (4) ◽  
pp. 1244-1253 ◽  
Author(s):  
Sophie Brinster ◽  
Sylviane Furlan ◽  
Pascale Serror
Keyword(s):  
Cell Wall ◽  
Cell Surface ◽  
Enterococcus Faecalis ◽  
Surface Proteins ◽  
Reporter Protein ◽  
Gram Positive ◽  
Whole Cells ◽  
Gram Positive Bacteria ◽  
Cell Wall Binding ◽  
Genes Encoding

ABSTRACT Analysis of the genome sequence of Enterococcus faecalis clinical isolate V583 revealed novel genes encoding surface proteins. Twenty-seven of these proteins, annotated as having unknown functions, possess a putative N-terminal signal peptide and a conserved C-terminal region characterized by a novel conserved domain designated WxL. Proteins having similar characteristics were also detected in other low-G+C-content gram-positive bacteria. We hypothesized that the WxL region might be a determinant of bacterial cell location. This hypothesis was tested by generating protein fusions between the C-terminal regions of two WxL proteins in E. faecalis and a nuclease reporter protein. We demonstrated that the C-terminal regions of both proteins conferred a cell surface localization to the reporter fusions in E. faecalis. This localization was eliminated by introducing specific deletions into the domains. Interestingly, exogenously added protein fusions displayed binding to whole cells of various gram-positive bacteria. We also showed that the peptidoglycan was a binding ligand for WxL domain attachment to the cell surface and that neither proteins nor carbohydrates were necessary for binding. Based on our findings, we propose that the WxL region is a novel cell wall binding domain in E. faecalis and other gram-positive bacteria.

scholarly journals A Novel Dual-creMotif Enables Two-Way Autoregulation of CcpA inClostridium acetobutylicum

2018 ◽  
Vol 84 (8) ◽  
pp. e00114-18 ◽  
Author(s):  
Lu Zhang ◽  
Yanqiang Liu ◽  
Yunpeng Yang ◽  
Weihong Jiang ◽  
Yang Gu
Keyword(s):  
Regulatory Network ◽  
Target Genes ◽  
Protein A ◽  
Cell Physiology ◽  
Coding Region ◽  
Gram Positive ◽  
Content Type ◽  
Gram Positive Bacteria

ABSTRACTThe master regulator CcpA (catabolite control protein A) manages a large and complex regulatory network that is essential for cellular physiology and metabolism in Gram-positive bacteria. Although CcpA can affect the expression of target genes by binding to acis-acting catabolite-responsive element (cre), whether and how the expression of CcpA is regulated remain poorly explored. Here, we report a novel dual-cremotif that is employed by the CcpA inClostridium acetobutylicum, a typical solventogenicClostridiumspecies, for autoregulation. Twocresites are involved in CcpA autoregulation, and they reside in the promoter and coding regions of CcpA. In this dual-cremotif,creP, in the promoter region, positively regulatesccpAtranscription, whereascreORF, in the coding region, negatively regulates this transcription, thus enabling two-way autoregulation of CcpA. Although CcpA boundcrePmore strongly thancreORFin vitro, thein vivoassay showed thatcreORF-based repression dominates CcpA autoregulation during the entire fermentation. Finally, a synonymous mutation ofcreORFwas made within the coding region, achieving an increased intracellular CcpA expression and improved cellular performance. This study provides new insights into the regulatory role of CcpA inC. acetobutylicumand, moreover, contributes a new engineering strategy for this industrial strain.IMPORTANCECcpA is known to be a key transcription factor in Gram-positive bacteria. However, it is still unclear whether and how the intracellular CcpA level is regulated, which may be essential for maintaining normal cell physiology and metabolism. We discovered here that CcpA employs a dual-cremotif to autoregulate, enabling dynamic control of its own expression level during the entire fermentation process. This finding answers the questions above and fills a void in our understanding of the regulatory network of CcpA. Interference in CcpA autoregulation leads to improved cellular performance, providing a new useful strategy in genetic engineering ofC. acetobutylicum. Since CcpA is widespread in Gram-positive bacteria, including pathogens, this dual-cre-based CcpA autoregulation would be valuable for increasing our understanding of CcpA-based global regulation in bacteria.

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