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Coppinger M, Yang L, Popham DL, Ruby E, Stabb EV. Transient infection of Euprymna scolopes with an engineered D-alanine auxotroph of Vibrio fischeri. Appl Environ Microbiol 2024:e0129824. [PMID: 39235243 DOI: 10.1128/aem.01298-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2024] [Accepted: 08/10/2024] [Indexed: 09/06/2024] Open
Abstract
The symbiosis between Vibrio fischeri and the Hawaiian bobtail squid, Euprymna scolopes, is a tractable and well-studied model of bacteria-animal mutualism. Here, we developed a method to transiently colonize E. scolopes using D-alanine (D-ala) auxotrophy of the symbiont, controlling the persistence of viable infection by supplying or withholding D-ala. We generated alanine racemase (alr) mutants of V. fischeri that lack avenues for mutational suppression of auxotrophy or reversion to prototrophy. Surprisingly, an ∆alr mutant did not require D-ala to grow in a minimal medium, a phenomenon requiring metC, which encodes cystathionine β-lyase. Likewise, overexpression of metC suppressed D-ala auxotrophy in a rich medium. To block potential mechanisms of suppression, we combined the ∆alr mutation with deletions of metC and/or bsrF, which encodes a broad-spectrum racemase and investigated the suppression rates of four D-ala auxotrophic strains. We then focused on ∆alr ∆bsrF mutant MC13, which has a suppression rate of <10-9. When D-ala was removed from a growing culture of MC13, cells rounded and lysed within 40 minutes. Transient colonization of E. scolopes was achieved by inoculating squid in seawater containing MC13 and D-ala, and then transferring the squid into water lacking D-ala, which resulted in loss of viable symbionts within hours. Interestingly, the symbionts within crypt 3 persisted longer than those of crypt 1, suggesting a difference in bacterial growth rate in distinct crypt environments. Our study highlights a new approach for inducing transient colonization and provides insight into the biogeography of the E. scolopes light organ.IMPORTANCEThe importance of this study is multi-faceted, providing a valuable methodological tool and insight into the biology of the symbiosis between Vibrio fischeri and Euprymna scolopes. First, the study sheds light on the critical role of D-ala for bacterial growth, and the underpinnings of D-ala synthesis. Our observations that metC obviates the need for D-ala supplementation of an alr mutant in minimal medium and that MetC-dependent growth correlates with D-ala in peptidoglycan, corroborate and extend previous findings in Escherichia coli regarding a role of MetC in D-ala production. Second, our isolation of robust D-ala auxotrophs led us to a novel method for studying the squid-Vibrio symbiosis, allowing for transient colonization without the use of antibiotics, and revealed intriguing differences in symbiont growth parameters in distinct light organ crypts. This work and the methodology developed will contribute to our understanding of the persistence and dynamics of V. fischeri within its host.
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Affiliation(s)
- Macey Coppinger
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Liu Yang
- Division of Biosphere Sciences and Engineering, California Institute of Technology, Pasadena, California, USA
| | - David L Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - Edward Ruby
- Division of Biosphere Sciences and Engineering, California Institute of Technology, Pasadena, California, USA
| | - Eric V Stabb
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA
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2
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Bollinger KW, Müh U, Ocius KL, Apostolos AJ, Pires MM, Helm RF, Popham DL, Weiss DS, Ellermeier CD. Identification of a family of peptidoglycan transpeptidases reveals that Clostridioides difficile requires noncanonical cross-links for viability. Proc Natl Acad Sci U S A 2024; 121:e2408540121. [PMID: 39150786 PMCID: PMC11348318 DOI: 10.1073/pnas.2408540121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2024] [Accepted: 07/12/2024] [Indexed: 08/18/2024] Open
Abstract
Most bacteria are surrounded by a cell wall that contains peptidoglycan (PG), a large polymer composed of glycan strands held together by short peptide cross-links. There are two major types of cross-links, termed 4-3 and 3-3 based on the amino acids involved. 4-3 cross-links are created by penicillin-binding proteins, while 3-3 cross-links are created by L,D-transpeptidases (LDTs). In most bacteria, the predominant mode of cross-linking is 4-3, and these cross-links are essential for viability, while 3-3 cross-links comprise only a minor fraction and are not essential. However, in the opportunistic intestinal pathogen Clostridioides difficile, about 70% of the cross-links are 3-3. We show here that 3-3 cross-links and LDTs are essential for viability in C. difficile. We also show that C. difficile has five LDTs, three with a YkuD catalytic domain as in all previously known LDTs and two with a VanW catalytic domain, whose function was until now unknown. The five LDTs exhibit extensive functional redundancy. VanW domain proteins are found in many gram-positive bacteria but scarce in other lineages. We tested seven non-C. difficile VanW domain proteins and confirmed LDT activity in three cases. In summary, our findings uncover a previously unrecognized family of PG cross-linking enzymes, assign a catalytic function to VanW domains, and demonstrate that 3-3 cross-linking is essential for viability in C. difficile, the first time this has been shown in any bacterial species. The essentiality of LDTs in C. difficile makes them potential targets for antibiotics that kill C. difficile selectively.
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Affiliation(s)
- Kevin W. Bollinger
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA52242
| | - Ute Müh
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA52242
| | - Karl L. Ocius
- Department of Chemistry, University of Virginia, Charlottesville, VA22904
| | | | - Marcos M. Pires
- Department of Chemistry, University of Virginia, Charlottesville, VA22904
| | - Richard F. Helm
- Department of Biochemistry, Virginia Tech, Blacksburg, VA24061
| | - David L. Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA24061
| | - David S. Weiss
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA52242
- Graduate Program in Genetics, University of Iowa, Iowa City, IA52242
| | - Craig D. Ellermeier
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA52242
- Graduate Program in Genetics, University of Iowa, Iowa City, IA52242
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Coppinger MN, Laramore K, Popham DL, Stabb EV. A prototrophic suppressor of a Vibrio fischeri D-glutamate auxotroph reveals a member of the periplasmic broad-spectrum racemase family (BsrF). J Bacteriol 2024; 206:e0033323. [PMID: 38411059 PMCID: PMC10955857 DOI: 10.1128/jb.00333-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Accepted: 02/04/2024] [Indexed: 02/28/2024] Open
Abstract
Although bacterial peptidoglycan (PG) is highly conserved, some natural variations in PG biosynthesis and structure have evolved. Understanding the mechanisms and limits of such variation will inform our understanding of antibiotic resistance, innate immunity, and the evolution of bacteria. We have explored the constraints on PG evolution by blocking essential steps in PG biosynthesis in Vibrio fischeri and then selecting mutants with restored prototrophy. Here, we attempted to select prototrophic suppressors of a D-glutamate auxotrophic murI racD mutant. No suppressors were isolated on unsupplemented lysogeny broth salts (LBS), despite plating >1011 cells, nor were any suppressors generated through mutagenesis with ethyl methanesulfonate. A single suppressor was isolated on LBS supplemented with iso-D-gln, although the iso-D-gln subsequently appeared irrelevant. This suppressor has a genomic amplification formed by the creation of a novel junction that fuses proB to a gene encoding a putative broad-spectrum racemase of V. fischeri, bsrF. An engineered bsrF allele lacking the putative secretion signal (ΔSS-bsrF) also suppressed D-glu auxotrophy, resulting in PG that was indistinguishable from the wild type. The ΔSS-bsrF allele similarly suppressed the D-alanine auxotrophy of an alr mutant and restored prototrophy to a murI alr double mutant auxotrophic for both D-ala and D-glu. The ΔSS-bsrF allele increased resistance to D-cycloserine but had no effect on sensitivity to PG-targeting antibiotics penicillin, ampicillin, or vancomycin. Our work helps define constraints on PG evolution and reveals a periplasmic broad-spectrum racemase in V. fischeri that can be co-opted for PG biosynthesis, with concomitant D-cycloserine resistance. IMPORTANCE D-Amino acids are used and produced by organisms across all domains of life, but often, their origins and roles are not well understood. In bacteria, D-ala and D-glu are structural components of the canonical peptidoglycan cell wall and are generated by dedicated racemases Alr and MurI, respectively. The more recent discovery of additional bacterial racemases is broadening our view and deepening our understanding of D-amino acid metabolism. Here, while exploring alternative PG biosynthetic pathways in Vibrio fischeri, we unexpectedly shed light on an unusual racemase, BsrF. Our results illustrate a novel mechanism for the evolution of antibiotic resistance and provide a new avenue for exploring the roles of non-canonical racemases and D-amino acids in bacteria.
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Affiliation(s)
- Macey N. Coppinger
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
- Department of Biological Sciences, University of Illinois, Chicago, Illinois, USA
| | - Kathrin Laramore
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
| | - David L. Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - Eric V. Stabb
- Department of Biological Sciences, University of Illinois, Chicago, Illinois, USA
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4
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Bollinger KW, Müh U, Ocius KL, Apostolos AJ, Pires MM, Helm RF, Popham DL, Weiss DS, Ellermeier CD. Identification of a new family of peptidoglycan transpeptidases reveals atypical crosslinking is essential for viability in Clostridioides difficile. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.14.584917. [PMID: 38559057 PMCID: PMC10980060 DOI: 10.1101/2024.03.14.584917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Clostridioides difficile, the leading cause of antibiotic-associated diarrhea, relies primarily on 3-3 crosslinks created by L,D-transpeptidases (LDTs) to fortify its peptidoglycan (PG) cell wall. This is unusual, as in most bacteria the vast majority of PG crosslinks are 4-3 crosslinks, which are created by penicillin-binding proteins (PBPs). Here we report the unprecedented observation that 3-3 crosslinking is essential for viability in C. difficile. We also report the discovery of a new family of LDTs that use a VanW domain to catalyze 3-3 crosslinking rather than a YkuD domain as in all previously known LDTs. Bioinformatic analyses indicate VanW domain LDTs are less common than YkuD domain LDTs and are largely restricted to Gram-positive bacteria. Our findings suggest that LDTs might be exploited as targets for antibiotics that kill C. difficile without disrupting the intestinal microbiota that is important for keeping C. difficile in check.
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Affiliation(s)
- Kevin W. Bollinger
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Ute Müh
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Karl L. Ocius
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Alexis J. Apostolos
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
- Present address: Haleon, 1211 Sherwood Ave, Richmond, VA 23220
| | - Marcos M. Pires
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Richard F. Helm
- Department of Biochemistry, Virginia Tech, Blacksburg, VA, USA
| | - David L. Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | - David S. Weiss
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
- Graduate Program in Genetics, University of Iowa, Iowa City, IA USA
| | - Craig D. Ellermeier
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
- Graduate Program in Genetics, University of Iowa, Iowa City, IA USA
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Delerue T, Chareyre S, Anantharaman V, Gilmore MC, Popham DL, Cava F, Aravind L, Ramamurthi KS. Bacterial cell surface nanoenvironment requires a specialized chaperone to activate a peptidoglycan biosynthetic enzyme. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.06.561273. [PMID: 37986874 PMCID: PMC10659427 DOI: 10.1101/2023.10.06.561273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Bacillus subtilis spores are produced inside the cytosol of a mother cell. Spore surface assembly requires the SpoVK protein in the mother cell, but its function is unknown. Here, we report that SpoVK is a dedicated chaperone from a distinct higher-order clade of AAA+ ATPases that activates the peptidoglycan glycosyltransferase MurG during sporulation, even though MurG does not normally require activation by a chaperone during vegetative growth. MurG redeploys to the spore surface during sporulation, where we show that the local pH is reduced and propose that this change in cytosolic nanoenvironment necessitates a specific chaperone for proper MurG function. Further, we show that SpoVK participates in a developmental checkpoint in which improper spore surface assembly inactivates SpoVK, which leads to sporulation arrest. The AAA+ ATPase clade containing SpoVK includes other dedicated chaperones involved in secretion, cell-envelope biosynthesis, and carbohydrate metabolism, suggesting that such fine-tuning might be a widespread feature of different subcellular nanoenvironments.
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Affiliation(s)
- Thomas Delerue
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Sylvia Chareyre
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Vivek Anantharaman
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland, USA
| | - Michael C. Gilmore
- The Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå Center for Microbial Research (UCMR), Science for Life Laboratory (SciLifeLab), Department of Molecular Biology, Umeå University, Umeå, Sweden
| | - David L. Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - Felipe Cava
- The Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå Center for Microbial Research (UCMR), Science for Life Laboratory (SciLifeLab), Department of Molecular Biology, Umeå University, Umeå, Sweden
| | - L. Aravind
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland, USA
| | - Kumaran S. Ramamurthi
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA
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6
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Johnson D, Jiang W. Infectious diseases, autoantibodies, and autoimmunity. J Autoimmun 2023; 137:102962. [PMID: 36470769 PMCID: PMC10235211 DOI: 10.1016/j.jaut.2022.102962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Accepted: 11/27/2022] [Indexed: 12/04/2022]
Abstract
Infections are known to trigger flares of autoimmune diseases in humans and serve as an inciting cause of autoimmunity in animals. Evidence suggests a causative role of infections in triggering antigen-specific autoimmunity, previous thought mainly through antigen mimicry. However, an infection can induce bystander autoreactive T and B cell polyclonal activation, believed to result in non-pathogenic and pathogenic autoimmune responses. Lastly, epitope spreading in autoimmunity is a mechanism of epitope changes of autoreactive cells induced by infection, promoting the targeting of additional self-epitopes. This review highlights recent research findings, emphasizes infection-mediated autoimmune responses, and discusses the possible mechanisms involved.
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Affiliation(s)
- Douglas Johnson
- Department of Microbiology and Immunology, Medical University of South Carolina, 173 Ashley Ave., Charleston, SC, USA; Ralph H. Johnson VA Medical Center, Charleston, SC, USA
| | - Wei Jiang
- Department of Microbiology and Immunology, Medical University of South Carolina, 173 Ashley Ave., Charleston, SC, USA; Ralph H. Johnson VA Medical Center, Charleston, SC, USA; Divison of Infectious Disease, Department of Medicine, Medical University of South Carolina, Charleston, SC, USA.
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7
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Kwan JMC, Qiao Y. Mechanistic Insights into the Activities of Major Families of Enzymes in Bacterial Peptidoglycan Assembly and Breakdown. Chembiochem 2023; 24:e202200693. [PMID: 36715567 DOI: 10.1002/cbic.202200693] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 01/28/2023] [Accepted: 01/30/2023] [Indexed: 01/31/2023]
Abstract
Serving as an exoskeletal scaffold, peptidoglycan is a polymeric macromolecule that is essential and conserved across all bacteria, yet is absent in mammalian cells; this has made bacterial peptidoglycan a well-established excellent antibiotic target. In addition, soluble peptidoglycan fragments derived from bacteria are increasingly recognised as key signalling molecules in mediating diverse intra- and inter-species communication in nature, including in gut microbiota-host crosstalk. Each bacterial species encodes multiple redundant enzymes for key enzymatic activities involved in peptidoglycan assembly and breakdown. In this review, we discuss recent findings on the biochemical activities of major peptidoglycan enzymes, including peptidoglycan glycosyltransferases (PGT) and transpeptidases (TPs) in the final stage of peptidoglycan assembly, as well as peptidoglycan glycosidases, lytic transglycosylase (LTs), amidases, endopeptidases (EPs) and carboxypeptidases (CPs) in peptidoglycan turnover and metabolism. Biochemical characterisation of these enzymes provides valuable insights into their substrate specificity, regulation mechanisms and potential modes of inhibition.
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Affiliation(s)
- Jeric Mun Chung Kwan
- School of Chemistry, Chemical Engineering and Biotechnology (CCEB), 21 Nanyang Link, Singapore, 637371, Singapore.,LKC School of Medicine, Nanyang Technological University (NTU) Singapore, 11 Mandalay Road, Singapore, Singapore, 208232, Singapore
| | - Yuan Qiao
- School of Chemistry, Chemical Engineering and Biotechnology (CCEB), Nanyang Technological University (NTU), Singapore, 21 Nanyang Link, Singapore, 637371, Singapore
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Abstract
Clostridioides difficile spores are the infective form for this endospore-forming organism. The vegetative cells are intolerant to oxygen and poor competitors with a healthy gut microbiota. Therefore, in order for C. difficile to establish infection, the spores have to germinate in an environment that supports vegetative growth. To initiate germination, C. difficile uses Csp-type germinant receptors that consist of the CspC and CspA pseudoproteases as the bile acid and cogerminant receptors, respectively. CspB is a subtilisin-like protease that cleaves the inhibitory propeptide from the pro-SleC cortex lytic enzyme, thereby activating it and initiating cortex degradation. Though several locations have been proposed for where these proteins reside within the spore (i.e., spore coat, outer spore membrane, cortex, and inner spore membrane), these have been based, mostly, on hypotheses or prior data in Clostridium perfringens. In this study, we visualized the germination and outgrowth process using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and used immunogold labeling to visualize key germination regulators. These analyses localize these key regulators to the spore cortex region for the first time. IMPORTANCE Germination by C. difficile spores is the first step in the establishment of potentially life-threatening C. difficile infection (CDI). A deeper understanding of the mechanism by which spores germinate may provide insight for how to either prevent spore germination into a disease-causing vegetative form or trigger germination prematurely when the spore is either in the outside environment or in a host environment that does not support the establishment of colonization/disease.
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Amon JD, Artzi L, Rudner DZ. Genetic Evidence for Signal Transduction within the Bacillus subtilis GerA Germinant Receptor. J Bacteriol 2022; 204:e0047021. [PMID: 34780301 PMCID: PMC8846391 DOI: 10.1128/jb.00470-21] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 11/06/2021] [Indexed: 11/20/2022] Open
Abstract
Bacterial spores can rapidly exit dormancy through the process of germination. This process begins with the activation of nutrient receptors embedded in the spore membrane. The prototypical germinant receptor in Bacillus subtilis responds to l-alanine and is thought to be a complex of proteins encoded by the genes in the gerA operon: gerAA, gerAB, and gerAC. The GerAB subunit has recently been shown to function as the nutrient sensor, but beyond contributing to complex stability, no additional functions have been attributed to the other two subunits. Here, we investigate the role of GerAA. We resurrect a previously characterized allele of gerA (termed gerA*) that carries a mutation in gerAA and show that it constitutively activates germination even in the presence of a wild-type copy of gerA. Using an enrichment strategy to screen for suppressors of gerA*, we identified mutations in all three gerA genes that restore a functional receptor. Characterization of two distinct gerAB suppressors revealed that one (gerAB[E105K]) reduces the GerA complex's ability to respond to l-alanine, while another (gerAB[F259S]) disrupts the germinant signal downstream of l-alanine recognition. These data argue against models in which GerAA is directly or indirectly involved in germinant sensing. Rather, our data suggest that GerAA is responsible for transducing the nutrient signal sensed by GerAB. While the steps downstream of gerAA have yet to be uncovered, these results validate the use of a dominant-negative genetic approach in elucidating the gerA signal transduction pathway. IMPORTANCE Endospore formers are a broad group of bacteria that can enter dormancy upon starvation and exit dormancy upon sensing the return of nutrients. How dormant spores sense and respond to these nutrients is poorly understood. Here, we identify a key step in the signal transduction pathway that is activated after spores detect the amino acid l-alanine. We present a model that provides a more complete picture of this process that is critical for allowing dormant spores to germinate and resume growth.
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Affiliation(s)
- Jeremy D. Amon
- Department of Microbiology, Harvard Medical School, Boston, Massachusetts, USA
| | - Lior Artzi
- Department of Microbiology, Harvard Medical School, Boston, Massachusetts, USA
| | - David Z. Rudner
- Department of Microbiology, Harvard Medical School, Boston, Massachusetts, USA
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Baloh M, Sorg JA. Clostridioides difficile spore germination: initiation to DPA release. Curr Opin Microbiol 2022; 65:101-107. [PMID: 34808546 PMCID: PMC8792321 DOI: 10.1016/j.mib.2021.11.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 11/01/2021] [Accepted: 11/04/2021] [Indexed: 02/03/2023]
Abstract
Germination by Clostridioides difficile spores is an essential step in pathogenesis. Spores are metabolically dormant forms of bacteria that resist severe conditions. Work over the last 10 years has elucidated that C. difficile spores germinate thorough a novel pathway. This review summarizes our understanding of C. difficile spore germination and the factors involved in germinant recognition, cortex degradation and DPA release.
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Affiliation(s)
- Marko Baloh
- Department of Biology, Texas A&M University, College Station, TX 77843
| | - Joseph A. Sorg
- Department of Biology, Texas A&M University, College Station, TX 77843,Corresponding author: ph: 979-845-6299,
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11
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Coullon H, Candela T. Clostridioides difficile peptidoglycan modifications. Curr Opin Microbiol 2021; 65:156-161. [PMID: 34883390 DOI: 10.1016/j.mib.2021.11.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Revised: 11/13/2021] [Accepted: 11/17/2021] [Indexed: 11/29/2022]
Abstract
The cortex and peptidoglycan of Clostridioides difficile have been poorly investigated. This last decade, the interest increased because these two structures are highly modified and these modifications may be involved in antimicrobial resistance. For example, C. difficile peptidoglycan deacetylation was recently reported to be involved in lysozyme resistance. Modifications may also be important for spore cortex synthesis or spore germination, which is essential in C. difficile pathogenesis. As such, the enzymes responsible for modifications of the peptidoglycan and/or cortex could be new drug target candidates or used as anti-C. difficile agents, as seen for the CD11 autolysin. In this review, we focus on C. difficile peptidoglycan and cortex and compare their structures with those of other well studied bacteria.
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Affiliation(s)
- Héloise Coullon
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France; Division of Infectious Diseases, Dept. of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Thomas Candela
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France.
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12
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Coullon H, Rifflet A, Wheeler R, Janoir C, Boneca IG, Candela T. Peptidoglycan analysis reveals that synergistic deacetylase activity in vegetative Clostridium difficile impacts the host response. J Biol Chem 2020; 295:16785-16796. [PMID: 32978253 PMCID: PMC7864072 DOI: 10.1074/jbc.ra119.012442] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Revised: 09/23/2020] [Indexed: 12/21/2022] Open
Abstract
Clostridium difficile is an anaerobic and spore-forming bacterium responsible for 15-25% of postantibiotic diarrhea and 95% of pseudomembranous colitis. Peptidoglycan is a crucial element of the bacterial cell wall that is exposed to the host, making it an important target for the innate immune system. The C. difficile peptidoglycan is largely N-deacetylated on its glucosamine (93% of muropeptides) through the activity of enzymes known as N-deacetylases, and this N-deacetylation modulates host-pathogen interactions, such as resistance to the bacteriolytic activity of lysozyme, virulence, and host innate immune responses. C. difficile genome analysis showed that 12 genes potentially encode N-deacetylases; however, which of these N-deacetylases are involved in peptidoglycan N-deacetylation remains unknown. Here, we report the enzymes responsible for peptidoglycan N-deacetylation and their respective regulation. Through peptidoglycan analysis of several mutants, we found that the N-deacetylases PdaV and PgdA act in synergy. Together they are responsible for the high level of peptidoglycan N-deacetylation in C. difficile and the consequent resistance to lysozyme. We also characterized a third enzyme, PgdB, as a glucosamine N-deacetylase. However, its impact on N-deacetylation and lysozyme resistance is limited, and its physiological role remains to be dissected. Finally, given the influence of peptidoglycan N-deacetylation on host defense against pathogens, we investigated the virulence and colonization ability of the mutants. Unlike what has been shown in other pathogenic bacteria, a lack of N-deacetylation in C. difficile is not linked to a decrease in virulence.
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Affiliation(s)
- Héloise Coullon
- Université Paris-Saclay, INRAE, AgroParisTech, Université Paris-Saclay, Jouy-en-Josas, France
| | - Aline Rifflet
- Institut Pasteur, Unité Biologie et Génétique de la Paroi Bactérienne, Paris, France; INSERM, Équipe Avenir, Paris; CNRS, UMR 2001 "Microbiologie Intégrative et Moléculaire," Paris, France
| | - Richard Wheeler
- Institut Pasteur, Unité Biologie et Génétique de la Paroi Bactérienne, Paris, France; INSERM, Équipe Avenir, Paris; CNRS, UMR 2001 "Microbiologie Intégrative et Moléculaire," Paris, France
| | - Claire Janoir
- Université Paris-Saclay, INRAE, AgroParisTech, Université Paris-Saclay, Jouy-en-Josas, France
| | - Ivo G Boneca
- Institut Pasteur, Unité Biologie et Génétique de la Paroi Bactérienne, Paris, France; INSERM, Équipe Avenir, Paris; CNRS, UMR 2001 "Microbiologie Intégrative et Moléculaire," Paris, France
| | - Thomas Candela
- Université Paris-Saclay, INRAE, AgroParisTech, Université Paris-Saclay, Jouy-en-Josas, France.
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Fu Y, Liang L, Deng S, Wu Y, Yuan Y, Gao M. Novel spore lytic enzyme from a Bacillus phage leading to spore killing. Enzyme Microb Technol 2020; 142:109698. [PMID: 33220860 DOI: 10.1016/j.enzmictec.2020.109698] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 10/19/2020] [Accepted: 10/20/2020] [Indexed: 01/03/2023]
Abstract
Bacterial spores maintain metabolic dormancy and have high resistance to external pressure. Germination requires degradation of the spore cortex and the participation of germination-specific cortex-lytic enzymes (GSLEs). Previously reported GSLEs have been identified in bacteria and facilitate germination. In this study, we have characterized a novel spore lytic enzyme, Ply67, from Bacillus pumilus phage vB_BpuM_BpSp. Ply67 had a similar cortex-lytic activity to GSLEs but disrupted the inner membranes (IMs) of spores, leading to spore killing rather than germination. The amino acid sequence of the complete protein, Ply67FL, exhibited 40% homology to the GSLE SleB. Domain prediction showed that Ply67FL was composed of three domains: a signal peptide, N-terminal domain protein and C-terminal domain protein. Ply67FL rapidly caused E. coli cells lysis when it was expressed in E. coli. The protein containing the C-terminal domain protein, Ply67C, could kill B. pumilus spores. The protein containing the N-terminal domain protein, Ply67N, could combine with the decoated B. pumilus spores, indicating that N-terminal was the binding domain and C-terminal was the hydrolase domain. The protein lacking the signal peptide but containing the N-terminal and C-terminal domain proteins, Ply67, had activity against spores of various Bacillus species. The surface of spores treated with Ply67 shrank and the permeability barrier was disrupted, and the inner contents leaked out. Immunoelectron microscopic observation showed that Ply67 was mainly acted on the spore cortex. Overall, Ply67 is a novel spore lytic enzyme that differs from other GSLEs not only in amino acid sequence but also in activity against spores, and Ply67 might have the potential to kill spores of pathogenic Bacillus species, e.g., B. cereus and B. anthracis.
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Affiliation(s)
- Yajuan Fu
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, PR China; University of Chinese Academy of Sciences, Beijing, 100039, PR China
| | - Leiqin Liang
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, PR China; University of Chinese Academy of Sciences, Beijing, 100039, PR China
| | - Sangsang Deng
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, PR China; University of Chinese Academy of Sciences, Beijing, 100039, PR China
| | - Yan Wu
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, PR China
| | - Yihui Yuan
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, PR China
| | - Meiying Gao
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430071, PR China.
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14
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Kaus GM, Snyder LF, Müh U, Flores MJ, Popham DL, Ellermeier CD. Lysozyme Resistance in Clostridioides difficile Is Dependent on Two Peptidoglycan Deacetylases. J Bacteriol 2020; 202:e00421-20. [PMID: 32868404 PMCID: PMC7585060 DOI: 10.1128/jb.00421-20] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Accepted: 08/25/2020] [Indexed: 12/18/2022] Open
Abstract
Clostridioides (Clostridium) difficile is a major cause of hospital-acquired infections leading to antibiotic-associated diarrhea. C. difficile exhibits a very high level of resistance to lysozyme. Bacteria commonly resist lysozyme through modification of the cell wall. In C. difficile, σV is required for lysozyme resistance, and σV is activated in response to lysozyme. Once activated, σV, encoded by csfV, directs transcription of genes necessary for lysozyme resistance. Here, we analyze the contribution of individual genes in the σV regulon to lysozyme resistance. Using CRISPR-Cas9-mediated mutagenesis we constructed in-frame deletions of single genes in the csfV operon. We find that pdaV, which encodes a peptidoglycan deacetylase, is partially responsible for lysozyme resistance. We then performed CRISPR inhibition (CRISPRi) to identify a second peptidoglycan deacetylase, encoded by pgdA, that is important for lysozyme resistance. Deletion of either pgdA or pdaV resulted in modest decreases in lysozyme resistance. However, deletion of both pgdA and pdaV resulted in a 1,000-fold decrease in lysozyme resistance. Further, muropeptide analysis revealed that loss of either PgdA or PdaV had modest effects on peptidoglycan deacetylation but that loss of both PgdA and PdaV resulted in almost complete loss of peptidoglycan deacetylation. This suggests that PgdA and PdaV are redundant peptidoglycan deacetylases. We also used CRISPRi to compare other lysozyme resistance mechanisms and conclude that peptidoglycan deacetylation is the major mechanism of lysozyme resistance in C. difficileIMPORTANCEClostridioides difficile is the leading cause of hospital-acquired diarrhea. C. difficile is highly resistant to lysozyme. We previously showed that the csfV operon is required for lysozyme resistance. Here, we used CRISPR-Cas9 mediated mutagenesis and CRISPRi knockdown to show that peptidoglycan deacetylation is necessary for lysozyme resistance and is the major lysozyme resistance mechanism in C. difficile We show that two peptidoglycan deacetylases in C. difficile are partially redundant and are required for lysozyme resistance. PgdA provides an intrinsic level of deacetylation, and PdaV, encoded by a part of the csfV operon, provides lysozyme-induced peptidoglycan deacetylation.
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Affiliation(s)
- Gabriela M Kaus
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - Lindsey F Snyder
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, Iowa, USA
| | - Ute Müh
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
| | - Matthew J Flores
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - David L Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - Craig D Ellermeier
- Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, Iowa, USA
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15
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Amon JD, Yadav AK, Ramirez-Guadiana FH, Meeske AJ, Cava F, Rudner DZ. SwsB and SafA Are Required for CwlJ-Dependent Spore Germination in Bacillus subtilis. J Bacteriol 2020; 202:e00668-19. [PMID: 31871031 PMCID: PMC7043669 DOI: 10.1128/jb.00668-19] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 12/13/2019] [Indexed: 02/07/2023] Open
Abstract
When Bacillus subtilis spores detect nutrients, they exit dormancy through the processes of germination and outgrowth. A key step in germination is the activation of two functionally redundant cell wall hydrolases (SleB and CwlJ) that degrade the specialized cortex peptidoglycan that surrounds the spore. How these enzymes are regulated remains poorly understood. To identify additional factors that affect their activity, we used transposon sequencing to screen for synthetic germination defects in spores lacking SleB or CwlJ. Other than the previously characterized protein YpeB, no additional factors were found to be specifically required for SleB activity. In contrast, our screen identified SafA and YlxY (renamed SwsB) in addition to the known factors GerQ and CotE as proteins required for CwlJ function. SafA is a member of the spore's proteinaceous coat and we show that, like GerQ and CotE, it is required for accumulation and retention of CwlJ in the dormant spore. SwsB is broadly conserved among spore formers, and we show that it is required for CwlJ to efficiently degrade the cortex during germination. Intriguingly, SwsB resembles polysaccharide deacetylases, and its putative catalytic residues are required for its role in germination. However, we find no chemical signature of its activity on the spore cortex or in vitro While the precise, mechanistic role of SwsB remains unknown, we explore and discuss potential activities.IMPORTANCE Spore formation in Bacillus subtilis has been studied for over half a century, and virtually every step in this developmental process has been characterized in molecular detail. In contrast, how spores exit dormancy remains less well understood. A key step in germination is the degradation of the specialized cell wall surrounding the spore called the cortex. Two enzymes (SleB and CwlJ) specifically target this protective layer, but how they are regulated and whether additional factors promote their activity are unknown. Here, we identified the coat protein SafA and a conserved but uncharacterized protein YlxY as additional factors required for CwlJ-dependent degradation of the cortex. Our analysis provides a more complete picture of this essential step in the exit from dormancy.
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Affiliation(s)
- Jeremy D Amon
- Department of Microbiology, Harvard Medical School, Boston, Massachusetts, USA
| | - Akhilesh K Yadav
- Laboratory for Molecular Infection Medicine, Department of Molecular Biology, Umeå University, Umeå, Sweden
- Analytical Chemistry Division, CSIR-Indian Institute of Toxicology Research, Lucknow, India
| | | | - Alexander J Meeske
- Department of Microbiology, Harvard Medical School, Boston, Massachusetts, USA
| | - Felipe Cava
- Laboratory for Molecular Infection Medicine, Department of Molecular Biology, Umeå University, Umeå, Sweden
| | - David Z Rudner
- Department of Microbiology, Harvard Medical School, Boston, Massachusetts, USA
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16
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Aspholm ME, Kollerud KK, Høgberg Hansen HC, Granum PE, Christie G, Lindbäck T. Biochemical and mutational analysis of spore cortex-lytic enzymes in the food spoiler Bacillus licheniformis. Food Microbiol 2019; 84:103259. [PMID: 31421778 DOI: 10.1016/j.fm.2019.103259] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 07/01/2019] [Accepted: 07/03/2019] [Indexed: 12/11/2022]
Abstract
Bacillus licheniformis is frequently associated with food spoilage due to its ability to form highly resistant endospores. The present study reveals that B. licheniformis spore peptidoglycan shares a similar structure to spores of other species of Bacillus. Two enzymatic activities associated with depolymerisation of the cortical peptidoglycan, which represents a crucial step in spore germination, were detected by muropeptide analysis. These include lytic transglycosylase and N-acetylglucosaminidase activity, with non-lytic epimerase activity also being detected. The role of various putative cortex-lytic enzymes that account for the aforementioned activity was investigated by mutational analysis. These analyses indicate that SleB is the major lysin involved in cortex depolymerisation in B. licheniformis spores, with CwlJ and SleL having lesser roles. Collectively, the results of this work indicate that B. licheniformis spores employ a similar approach for cortical depolymerisation during germination as spores of other Bacillus species.
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Affiliation(s)
- Marina E Aspholm
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Pb 369 Sentrum, 0102, Oslo, Norway
| | - Kristian K Kollerud
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Pb 369 Sentrum, 0102, Oslo, Norway
| | - Helge C Høgberg Hansen
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Pb 369 Sentrum, 0102, Oslo, Norway
| | - Per Einar Granum
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Pb 369 Sentrum, 0102, Oslo, Norway
| | - Graham Christie
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, United Kingdom
| | - Toril Lindbäck
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Pb 369 Sentrum, 0102, Oslo, Norway.
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17
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Coullon H, Rifflet A, Wheeler R, Janoir C, Boneca IG, Candela T. N-Deacetylases required for muramic-δ-lactam production are involved in Clostridium difficile sporulation, germination, and heat resistance. J Biol Chem 2018; 293:18040-18054. [PMID: 30266804 DOI: 10.1074/jbc.ra118.004273] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 09/24/2018] [Indexed: 01/08/2023] Open
Abstract
Spores are produced by many organisms as a survival mechanism activated in response to several environmental stresses. Bacterial spores are multilayered structures, one of which is a peptidoglycan layer called the cortex, containing muramic-δ-lactams that are synthesized by at least two bacterial enzymes, the muramoyl-l-alanine amidase CwlD and the N-deacetylase PdaA. This study focused on the spore cortex of Clostridium difficile, a Gram-positive, toxin-producing anaerobic bacterial pathogen that can colonize the human intestinal tract and is a leading cause of antibiotic-associated diarrhea. Using ultra-HPLC coupled with high-resolution MS, here we found that the spore cortex of the C. difficile 630Δerm strain differs from that of Bacillus subtilis Among these differences, the muramic-δ-lactams represented only 24% in C. difficile, compared with 50% in B. subtilis CD630_14300 and CD630_27190 were identified as genes encoding the C. difficile N-deacetylases PdaA1 and PdaA2, required for muramic-δ-lactam synthesis. In a pdaA1 mutant, only 0.4% of all muropeptides carried a muramic-δ-lactam modification, and muramic-δ-lactams were absent in the cortex of a pdaA1-pdaA2 double mutant. Of note, the pdaA1 mutant exhibited decreased sporulation, altered germination, decreased heat resistance, and delayed virulence in a hamster infection model. These results suggest a much greater role for muramic-δ-lactams in C. difficile than in other bacteria, including B. subtilis In summary, the spore cortex of C. difficile contains lower levels of muramic-δ-lactams than that of B. subtilis, and PdaA1 is the major N-deacetylase for muramic-δ-lactam biosynthesis in C. difficile, contributing to sporulation, heat resistance, and virulence.
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Affiliation(s)
- Héloise Coullon
- From the EA4043 Unité Bactéries Pathogènes et Santé (UBaPS), Université Paris-Sud, Université Paris-Saclay, 92290 Châtenay-Malabry
| | - Aline Rifflet
- the Institut Pasteur, Unité Biologie et Génétique de la Paroi Bactérienne, 75724 Paris, and; INSERM, Équipe Avenir, 75015 Paris, France
| | - Richard Wheeler
- the Institut Pasteur, Unité Biologie et Génétique de la Paroi Bactérienne, 75724 Paris, and; INSERM, Équipe Avenir, 75015 Paris, France
| | - Claire Janoir
- From the EA4043 Unité Bactéries Pathogènes et Santé (UBaPS), Université Paris-Sud, Université Paris-Saclay, 92290 Châtenay-Malabry
| | - Ivo Gomperts Boneca
- the Institut Pasteur, Unité Biologie et Génétique de la Paroi Bactérienne, 75724 Paris, and; INSERM, Équipe Avenir, 75015 Paris, France
| | - Thomas Candela
- From the EA4043 Unité Bactéries Pathogènes et Santé (UBaPS), Université Paris-Sud, Université Paris-Saclay, 92290 Châtenay-Malabry,.
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18
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Jones RM, Popham DL, Schmidt AL, Neidle EL, Stabb EV. Vibrio fischeri DarR Directs Responses to d-Aspartate and Represents a Group of Similar LysR-Type Transcriptional Regulators. J Bacteriol 2018; 200:e00773-17. [PMID: 29437849 PMCID: PMC6040199 DOI: 10.1128/jb.00773-17] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Accepted: 01/24/2018] [Indexed: 01/11/2023] Open
Abstract
Mounting evidence suggests that d-amino acids play previously underappreciated roles in diverse organisms. In bacteria, even d-amino acids that are absent from canonical peptidoglycan (PG) may act as growth substrates, as signals, or in other functions. Given these proposed roles and the ubiquity of d-amino acids, the paucity of known d-amino-acid-responsive transcriptional control mechanisms in bacteria suggests that such regulation awaits discovery. We found that DarR, a LysR-type transcriptional regulator (LTTR), activates transcription in response to d-Asp. The d-Glu auxotrophy of a Vibrio fischerimurI::Tn mutant was suppressed, with the wild-type PG structure maintained, by a point mutation in darR This darR mutation resulted in the overexpression of an adjacent operon encoding a putative aspartate racemase, RacD, which compensated for the loss of the glutamate racemase encoded by murI Using transcriptional reporters, we found that wild-type DarR activated racD transcription in response to exogenous d-Asp but not upon the addition of l-Asp, l-Glu, or d-Glu. A DNA sequence typical of LTTR-binding sites was identified between darR and the divergently oriented racD operon, and scrambling this sequence eliminated activation of the reporter in response to d-Asp. In several proteobacteria, genes encoding LTTRs similar to DarR are linked to genes with predicted roles in d- and/or l-Asp metabolism. To test the functional similarities in another bacterium, darR and racD mutants were also generated in Acinetobacter baylyi In V. fischeri and A. baylyi, growth on d-Asp required the presence of both darR and racD Our results suggest that multiple bacteria have the ability to sense and respond to d-Asp.IMPORTANCE d-Amino acids are prevalent in the environment and are generated by organisms from all domains of life. Although some biological roles for d-amino acids are understood, in other cases, their functions remain uncertain. Given the ubiquity of d-amino acids, it seems likely that bacteria will initiate transcriptional responses to them. Elucidating d-amino acid-responsive regulators along with the genes they control will help uncover bacterial uses of d-amino acids. Here, we report the discovery of DarR, a novel LTTR in V. fischeri that mediates a transcriptional response to environmental d-Asp and underpins the catabolism of d-Asp. DarR represents the founding member of a group of bacterial homologs that we hypothesize control aspects of aspartate metabolism in response to d-Asp and/or to d-Asp-containing peptides.
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Affiliation(s)
- Richard M Jones
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
| | - David L Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - Alicia L Schmidt
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
| | - Ellen L Neidle
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
| | - Eric V Stabb
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
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19
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Diaz OR, Sayer CV, Popham DL, Shen A. Clostridium difficile Lipoprotein GerS Is Required for Cortex Modification and Thus Spore Germination. mSphere 2018; 3:e00205-18. [PMID: 29950380 PMCID: PMC6021603 DOI: 10.1128/msphere.00205-18] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 04/22/2018] [Indexed: 02/04/2023] Open
Abstract
Clostridium difficile, also known as Clostridioides difficile, is a Gram-positive, spore-forming bacterium that is a leading cause of antibiotic-associated diarrhea. C. difficile infections begin when its metabolically dormant spores germinate to form toxin-producing vegetative cells. Successful spore germination depends on the degradation of the cortex, a thick layer of modified peptidoglycan that maintains dormancy. Cortex degradation is mediated by the SleC cortex lytic enzyme, which is thought to recognize the cortex-specific modification muramic-δ-lactam. C. difficile cortex degradation also depends on the Peptostreptococcaceae-specific lipoprotein GerS for unknown reasons. In this study, we tested whether GerS regulates production of muramic-δ-lactam and thus controls the ability of SleC to recognize its cortex substrate. By comparing the muropeptide profiles of ΔgerS spores to those of spores lacking either CwlD or PdaA, both of which mediate cortex modification in Bacillus subtilis, we determined that C. difficile GerS, CwlD, and PdaA are all required to generate muramic-δ-lactam. Both GerS and CwlD were needed to cleave the peptide side chains from N-acetylmuramic acid, suggesting that these two factors act in concert. Consistent with this hypothesis, biochemical analyses revealed that GerS and CwlD directly interact and that CwlD modulates GerS incorporation into mature spores. Since ΔgerS, ΔcwlD, and ΔpdaA spores exhibited equivalent germination defects, our results indicate that C. difficile spore germination depends on cortex-specific modifications, reveal GerS as a novel regulator of these processes, and highlight additional differences in the regulation of spore germination in C. difficile relative to B. subtilis and other spore-forming organisms.IMPORTANCE The Gram-positive, spore-forming bacterium Clostridium difficile is a leading cause of antibiotic-associated diarrhea. Because C. difficile is an obligate anaerobe, its aerotolerant spores are essential for transmitting disease, and their germination into toxin-producing cells is necessary for causing disease. Spore germination requires the removal of the cortex, a thick layer of modified peptidoglycan that maintains spore dormancy. Cortex degradation is mediated by the SleC hydrolase, which is thought to recognize cortex-specific modifications. Cortex degradation also requires the GerS lipoprotein for unknown reasons. In our study, we tested whether GerS is required to generate cortex-specific modifications by comparing the cortex composition of ΔgerS spores to the cortex composition of spores lacking two putative cortex-modifying enzymes, CwlD and PdaA. These analyses revealed that GerS, CwlD, and PdaA are all required to generate cortex-specific modifications. Since loss of these modifications in ΔgerS, ΔcwlD, and ΔpdaA mutants resulted in spore germination and heat resistance defects, the SleC cortex lytic enzyme depends on cortex-specific modifications to efficiently degrade this protective layer. Our results further indicate that GerS and CwlD are mutually required for removing peptide chains from spore peptidoglycan and revealed a novel interaction between these proteins. Thus, our findings provide new mechanistic insight into C. difficile spore germination.
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Affiliation(s)
- Oscar R Diaz
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts, USA
- NIH Postbaccalaureate Research Education Program (PREP), Tufts University School of Medicine, Boston, Massachusetts, USA
| | - Cameron V Sayer
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - David L Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA
| | - Aimee Shen
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts, USA
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20
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Abstract
Bacterial endospores possess multiple integument layers, one of which is the cortex peptidoglycan wall. The cortex is essential for the maintenance of spore core dehydration and dormancy and contains structural modifications that differentiate it from vegetative cell peptidoglycan and determine its fate during spore germination. Following the engulfment stage of sporulation, the cortex is synthesized within the intermembrane space surrounding the forespore. Proteins responsible for cortex synthesis are produced in both the forespore and mother cell compartments. While some of these proteins also contribute to vegetative cell wall synthesis, others are sporulation specific. In order for the bacterial endospore to germinate and resume metabolism, the cortex peptidoglycan must first be degraded through the action of germination-specific lytic enzymes. These enzymes are present, yet inactive, in the dormant spore and recognize the muramic-δ-lactam modification present in the cortex. Germination-specific lytic enzymes across Bacillaceae and Clostridiaceae share this specificity determinant, which ensures that the spore cortex is hydrolyzed while the vegetative cell wall remains unharmed. Bacillus species tend to possess two redundant enzymes, SleB and CwlJ, capable of sufficient cortex degradation, while the clostridia have only one, SleC. Additional enzymes are often present that cannot initiate the cortex degradation process, but which can increase the rate of release of small fragments into the medium. Between the two families, the enzymes also differ in the enzymatic activities they possess and the mechanisms acting to restrict their activation until germination has been initiated.
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21
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Omardien S, Brul S, Zaat SAJ. Antimicrobial Activity of Cationic Antimicrobial Peptides against Gram-Positives: Current Progress Made in Understanding the Mode of Action and the Response of Bacteria. Front Cell Dev Biol 2016; 4:111. [PMID: 27790614 PMCID: PMC5063857 DOI: 10.3389/fcell.2016.00111] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2016] [Accepted: 09/21/2016] [Indexed: 01/11/2023] Open
Abstract
Antimicrobial peptides (AMPs) have been proposed as a novel class of antimicrobials that could aid the fight against antibiotic resistant bacteria. The mode of action of AMPs as acting on the bacterial cytoplasmic membrane has often been presented as an enigma and there are doubts whether the membrane is the sole target of AMPs. Progress has been made in clarifying the possible targets of these peptides, which is reported in this review with as focus gram-positive vegetative cells and spores. Numerical estimates are discussed to evaluate the possibility that targets, other than the membrane, could play a role in susceptibility to AMPs. Concerns about possible resistance that bacteria might develop to AMPs are addressed. Proteomics, transcriptomics, and other molecular techniques are reviewed in the context of explaining the response of bacteria to the presence of AMPs and to predict what resistance strategies might be. Emergent mechanisms are cell envelope stress responses as well as enzymes able to degrade and/or specifically bind (and thus inactivate) AMPs. Further studies are needed to address the broadness of the AMP resistance and stress responses observed.
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Affiliation(s)
- Soraya Omardien
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences, University of Amsterdam Amsterdam, Netherlands
| | - Stanley Brul
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences, University of Amsterdam Amsterdam, Netherlands
| | - Sebastian A J Zaat
- Department of Medical Microbiology, Center for Infection and Immunity Amsterdam, Academic Medical Center, University of Amsterdam Amsterdam, Netherlands
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22
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Francis MB, Sorg JA. Detecting Cortex Fragments During Bacterial Spore Germination. J Vis Exp 2016. [PMID: 27403726 DOI: 10.3791/54146] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The process of endospore germination in Clostridium difficile, and other Clostridia, increasingly is being found to differ from the model spore-forming bacterium, Bacillus subtilis. Germination is triggered by small molecule germinants and occurs without the need for macromolecular synthesis. Though differences exist between the mechanisms of spore germination in species of Bacillus and Clostridium, a common requirement is the hydrolysis of the peptidoglycan-like cortex which allows the spore core to swell and rehydrate. After rehydration, metabolism can begin and this, eventually, leads to outgrowth of a vegetative cell. The detection of hydrolyzed cortex fragments during spore germination can be difficult and the modifications to the previously described assays can be confusing or difficult to reproduce. Thus, based on our recent report using this assay, we detail a step-by-step protocol for the colorimetric detection of cortex fragments during bacterial spore germination.
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23
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Sandoz KM, Popham DL, Beare PA, Sturdevant DE, Hansen B, Nair V, Heinzen RA. Transcriptional Profiling of Coxiella burnetii Reveals Extensive Cell Wall Remodeling in the Small Cell Variant Developmental Form. PLoS One 2016; 11:e0149957. [PMID: 26909555 PMCID: PMC4766238 DOI: 10.1371/journal.pone.0149957] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Accepted: 02/05/2016] [Indexed: 11/19/2022] Open
Abstract
A hallmark of Coxiella burnetii, the bacterial cause of human Q fever, is a biphasic developmental cycle that generates biologically, ultrastructurally, and compositionally distinct large cell variant (LCV) and small cell variant (SCV) forms. LCVs are replicating, exponential phase forms while SCVs are non-replicating, stationary phase forms. The SCV has several properties, such as a condensed nucleoid and an unusual cell envelope, suspected of conferring enhanced environmental stability. To identify genetic determinants of the LCV to SCV transition, we profiled the C. burnetii transcriptome at 3 (early LCV), 5 (late LCV), 7 (intermediate forms), 14 (early SCV), and 21 days (late SCV) post-infection of Vero epithelial cells. Relative to early LCV, genes downregulated in the SCV were primarily involved in intermediary metabolism. Upregulated SCV genes included those involved in oxidative stress responses, arginine acquisition, and cell wall remodeling. A striking transcriptional signature of the SCV was induction (>7-fold) of five genes encoding predicted L,D transpeptidases that catalyze nonclassical 3-3 peptide cross-links in peptidoglycan (PG), a modification that can influence several biological traits in bacteria. Accordingly, of cross-links identified, muropeptide analysis showed PG of SCV with 46% 3-3 cross-links as opposed to 16% 3-3 cross-links for LCV. Moreover, electron microscopy revealed SCV with an unusually dense cell wall/outer membrane complex as compared to LCV with its clearly distinguishable periplasm and inner and outer membranes. Collectively, these results indicate the SCV produces a unique transcriptome with a major component directed towards remodeling a PG layer that likely contributes to Coxiella's environmental resistance.
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Affiliation(s)
- Kelsi M. Sandoz
- Coxiella Pathogenesis Section, Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - David L. Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Paul A. Beare
- Coxiella Pathogenesis Section, Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Daniel E. Sturdevant
- Genomics Unit, Research Technologies Branch, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Bryan Hansen
- Electron Microscopy Unit, Research Technologies Branch, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Vinod Nair
- Electron Microscopy Unit, Research Technologies Branch, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
| | - Robert A. Heinzen
- Coxiella Pathogenesis Section, Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America
- * E-mail:
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Tan IS, Weiss CA, Popham DL, Ramamurthi KS. A Quality-Control Mechanism Removes Unfit Cells from a Population of Sporulating Bacteria. Dev Cell 2015; 34:682-93. [PMID: 26387458 DOI: 10.1016/j.devcel.2015.08.009] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Revised: 04/10/2015] [Accepted: 08/10/2015] [Indexed: 11/25/2022]
Abstract
Recent discoveries of regulated cell death in bacteria have led to speculation about possible benefits that apoptosis-like pathways may confer to single-celled organisms. However, establishing how these pathways provide increased ecological fitness has remained difficult to determine. Here, we report a pathway in Bacillus subtilis in which regulated cell death maintains the fidelity of sporulation through selective removal of cells that misassemble the spore envelope. The spore envelope, which protects the dormant spore's genome from environmental insults, uses the protein SpoIVA as a scaffold for assembly. We found that disrupting envelope assembly activates a cell death pathway wherein the small protein CmpA acts as an adaptor to the AAA+ ClpXP protease to degrade SpoIVA, thereby halting sporulation and resulting in lysis of defective sporulating cells. We propose that removal of unfit cells from a population of terminally differentiating cells protects against evolutionary deterioration and ultimately loss of the sporulation program.
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Affiliation(s)
- Irene S Tan
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; NIH-Johns Hopkins University Graduate Partnership Program, Baltimore, MD 21218, USA
| | - Cordelia A Weiss
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - David L Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA
| | - Kumaran S Ramamurthi
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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25
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Blankenship BG, Heffron JD, Popham DL. Lytic enzyme-assisted germination of Bacillus anthracis and Bacillus subtilis spores. J Appl Microbiol 2015; 119:521-8. [PMID: 25963559 DOI: 10.1111/jam.12839] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 04/30/2015] [Accepted: 05/03/2015] [Indexed: 11/30/2022]
Abstract
AIMS The goal of this work was to determine conditions under which external application of a spore germination-specific lytic enzyme (GSLE) can increase the germination efficiency of spore populations. METHODS AND RESULTS The Bacillus anthracis GSLE SleB was applied to native and coat-disrupted B. anthracis and Bacillus subtilis spores. SleB was inactive on native spores but was able to trigger rapid germination of coat-disrupted spores. Using spores lacking their GSLEs or their germinant receptors to model poorly germinating spores, SleB application was able to increase colony-forming efficiency 100-fold for native spores and >1000-fold for coat-disrupted spores. SleB effects on GSLE-deficient spores were greater than on germinant receptor-deficient spores. CONCLUSIONS SleB treatment can increase spore germination efficiency. The greater effect of SleB on coat-disrupted spores is presumably due to the greater access afforded to the cortex. However, SleB apparently gained access to the cortex of native spores after they responded to nutrients and completed stage I of germination, which may result in the disruption of coat structure. SIGNIFICANCE AND IMPACT OF THE STUDY Treatment of spore populations with a GSLE can increase germination efficiency. Such a treatment might be utilized to increase the rapid activation of industrial spore-based products.
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Affiliation(s)
- B G Blankenship
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | | | - D L Popham
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
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26
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Meaney CA, Cartman ST, McClure PJ, Minton NP. Optimal spore germination in Clostridium botulinum ATCC 3502 requires the presence of functional copies of SleB and YpeB, but not CwlJ. Anaerobe 2015; 34:86-93. [PMID: 25937262 DOI: 10.1016/j.anaerobe.2015.04.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Revised: 04/10/2015] [Accepted: 04/28/2015] [Indexed: 10/23/2022]
Abstract
Germination, the process by which dormant endospores return to vegetative growth, is a critical process in the life cycle of the notorious pathogen Clostridium botulinum. Crucial is the degradation by hydrolytic enzymes of an inner peptidoglycan spore layer termed the cortex. Two mechanistically different systems of cortex lysis exist in spores of Clostridium species. C. botulinum ATCC 3502 harbours the Bacillus-like system of SleB, CwlJ and YpeB cortex lytic enzymes (CLEs). Through the construction of insertional gene knockout mutants in the sleB, cwlJ and ypeB genes of C. botulinum ATCC 3502 and the production of spores of each mutant strain, the effect on germination was assessed. This study demonstrates a reduced germination efficiency in spores carrying mutations in either sleB or ypeB with an approximate 2-fold reduction in heat resistant colony forming units (CFU/OD600) when plated on rich media. This reduction could be restored to wild-type levels by removing the spore coat and plating on media supplemented with lysozyme. It was observed that cwlJ spores displayed a similar germination efficiency as wild-type spores (P > 0.05). An optimal germinant commixture was identified to include a combination of l-alanine with sodium bicarbonate as it resulted in a 32% drop in OD600, while the additional incorporation of l-lactate resulted in a 57% decrease. Studies of the germination efficiency of spores prepared from all three CLE mutants was performed by monitoring the associated decrease in optical density but a germination defect was not observed in any of the CLE mutant strains. This was likely due to the lack of specificity of this particular assay. Taken together, these data indicate that functional copies of SleB and YpeB, but not CwlJ are required for the optimal germination of the spores of C. botulinum ATCC 3502.
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Affiliation(s)
- Carolyn A Meaney
- Clostridia Research Group, BBSRC/EPSRC Synthetic Biology Research Centre, School of Life Sciences, University of Nottingham, Nottingham NG7 2RD, UK
| | - Stephen T Cartman
- Clostridia Research Group, BBSRC/EPSRC Synthetic Biology Research Centre, School of Life Sciences, University of Nottingham, Nottingham NG7 2RD, UK
| | | | - Nigel P Minton
- Clostridia Research Group, BBSRC/EPSRC Synthetic Biology Research Centre, School of Life Sciences, University of Nottingham, Nottingham NG7 2RD, UK.
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27
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Wu X, Grover N, Paskaleva EE, Mundra RV, Page MA, Kane RS, Dordick JS. Characterization of the activity of the spore cortex lytic enzyme CwlJ1. Biotechnol Bioeng 2015; 112:1365-75. [DOI: 10.1002/bit.25565] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2014] [Revised: 01/27/2015] [Accepted: 02/02/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Xia Wu
- Howard P. Isermann Department of Chemical and Biological Engineering; Rensselaer Polytechnic Institute; 110 8th Street, Troy New York 12180
- Center for Biotechnology and Interdisciplinary Studies; Rensselaer Polytechnic Institute; Troy New York 12180
| | - Navdeep Grover
- Center for Biotechnology and Interdisciplinary Studies; Rensselaer Polytechnic Institute; Troy New York 12180
| | - Elena E. Paskaleva
- Center for Biotechnology and Interdisciplinary Studies; Rensselaer Polytechnic Institute; Troy New York 12180
| | - Ruchir V. Mundra
- Howard P. Isermann Department of Chemical and Biological Engineering; Rensselaer Polytechnic Institute; 110 8th Street, Troy New York 12180
- Center for Biotechnology and Interdisciplinary Studies; Rensselaer Polytechnic Institute; Troy New York 12180
| | - Martin A. Page
- U.S. Army Engineer Research and Development Center; Construction Engineering Research Laboratory; Champaign Illinois
| | - Ravi S. Kane
- Howard P. Isermann Department of Chemical and Biological Engineering; Rensselaer Polytechnic Institute; 110 8th Street, Troy New York 12180
- Center for Biotechnology and Interdisciplinary Studies; Rensselaer Polytechnic Institute; Troy New York 12180
| | - Jonathan S. Dordick
- Howard P. Isermann Department of Chemical and Biological Engineering; Rensselaer Polytechnic Institute; 110 8th Street, Troy New York 12180
- Center for Biotechnology and Interdisciplinary Studies; Rensselaer Polytechnic Institute; Troy New York 12180
- Department of Materials Science and Engineering; Department of Biology; Department of Biomedical Engineering; Rensselaer Polytechnic Institute; Troy New York 12180
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28
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Noue ACDL, Peters J, Gervais P, Martinez N, Perrier-Cornet JM, Natali F. Proton dynamics in bacterial spores, a neutron scattering investigation. EPJ WEB OF CONFERENCES 2015. [DOI: 10.1051/epjconf/20158302003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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29
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Johnson CM, Grossman AD. Identification of host genes that affect acquisition of an integrative and conjugative element in Bacillus subtilis. Mol Microbiol 2014; 93:1284-301. [PMID: 25069588 DOI: 10.1111/mmi.12736] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/26/2014] [Indexed: 01/28/2023]
Abstract
Conjugation, a major type of horizontal gene transfer in bacteria, involves transfer of DNA from a donor to a recipient using donor-encoded conjugation machinery. Using a high-throughput screen (Tn-seq), we identified genes in recipients that contribute to acquisition of the integrative and conjugative element ICEBs1 by Bacillus subtilis. We found that null mutations in some genes caused an increase, and others a decrease in conjugation efficiency. Some mutations affected conjugation only when present in recipients. Other mutations affected conjugation when present in donors or recipients. Most of the genes identified are known or predicted to affect the cell envelope. Several encode enzymes involved in phospholipid biosynthesis and one encodes a homologue of penicillin-binding proteins. Two of the genes identified also affected conjugation of Tn916, indicating that their roles in conjugation may be general. We did not identify any genes in recipients that were essential for ICEBs1 conjugation, indicating that if there are such genes, then these are either essential for cell growth or redundant. Our results indicate that acquisition of ICEBs1, and perhaps other conjugative elements, is robust and not easily avoided by mutation and that several membrane-related functions affect the efficiency of conjugation.
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Affiliation(s)
- Christopher M Johnson
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
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30
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Role of YpeB in cortex hydrolysis during germination of Bacillus anthracis spores. J Bacteriol 2014; 196:3399-409. [PMID: 25022853 DOI: 10.1128/jb.01899-14] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The infectious agent of the disease anthrax is the spore of Bacillus anthracis. Bacterial spores are extremely resistant to environmental stresses, which greatly hinders spore decontamination efforts. The spore cortex, a thick layer of modified peptidoglycan, contributes to spore dormancy and resistance by maintaining the low water content of the spore core. The cortex is degraded by germination-specific lytic enzymes (GSLEs) during spore germination, rendering the cells vulnerable to common disinfection techniques. This study investigates the relationship between SleB, a GSLE in B. anthracis, and YpeB, a protein necessary for SleB stability and function. The results indicate that ΔsleB and ΔypeB spores exhibit similar germination phenotypes and that the two proteins have a strict codependency for their incorporation into the dormant spore. In the absence of its partner protein, SleB or YpeB is proteolytically degraded soon after expression during sporulation, rather than escaping the developing spore. The three PepSY domains of YpeB were examined for their roles in the interaction with SleB. YpeB truncation mutants illustrate the necessity of a region beyond the first PepSY domain for SleB stability. Furthermore, site-directed mutagenesis of highly conserved residues within the PepSY domains resulted in germination defects corresponding to reduced levels of both SleB and YpeB in the mutant spores. These results identify residues involved in the stability of both proteins and reiterate their codependent relationship. It is hoped that the study of GSLEs and interacting proteins will lead to the use of GSLEs as targets for efficient activation of spore germination and facilitation of spore cleanup.
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31
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Jorgenson MA, Chen Y, Yahashiri A, Popham DL, Weiss DS. The bacterial septal ring protein RlpA is a lytic transglycosylase that contributes to rod shape and daughter cell separation in Pseudomonas aeruginosa. Mol Microbiol 2014; 93:113-28. [PMID: 24806796 DOI: 10.1111/mmi.12643] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/06/2014] [Indexed: 11/28/2022]
Abstract
Rare lipoprotein A (RlpA) is a widely conserved outer membrane protein of unknown function that has previously only been studied in Escherichia coli, where it localizes to the septal ring and scattered foci along the lateral wall, but mutants have no phenotypic change. Here we show rlpA mutants of Pseudomonas aeruginosa form chains of short, fat cells when grown in low osmotic strength media. These morphological defects indicate RlpA is needed for efficient separation of daughter cells and maintenance of rod shape. Analysis of peptidoglycan sacculi from an rlpA deletion mutant revealed increased tetra and hexasaccharides that lack stem peptides (hereafter called 'naked glycans'). Incubation of these sacculi with purified RlpA resulted in release of naked glycans containing 1,6-anhydro N-acetylmuramic acid ends. RlpA did not degrade sacculi from wild-type cells unless the sacculi were subjected to a limited digestion with an amidase to remove some of the stem peptides. Thus, RlpA is a lytic transglycosylase with a strong preference for naked glycan strands. We propose that RlpA activity is regulated in vivo by substrate availability, and that amidases and RlpA work in tandem to degrade peptidoglycan in the division septum and lateral wall.
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Affiliation(s)
- Matthew A Jorgenson
- Department of Microbiology, Carver College of Medicine, The University of Iowa, Iowa City, IA, 52242, USA
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32
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Turner RD, Vollmer W, Foster SJ. Different walls for rods and balls: the diversity of peptidoglycan. Mol Microbiol 2014; 91:862-74. [PMID: 24405365 PMCID: PMC4015370 DOI: 10.1111/mmi.12513] [Citation(s) in RCA: 122] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/08/2014] [Indexed: 01/22/2023]
Abstract
Peptidoglycan performs the essential role of resisting turgor in the cell walls of most bacteria. It determines cell shape, and its biosynthesis is the target for many important antibiotics. The fundamental chemical building blocks of peptidoglycan are conserved: repeating disaccharides cross-linked by peptides. However, these blocks come in many varieties and can be assembled in different ways. So beyond the fundamental similarity, prodigious chemical, organizational and architectural diversity is revealed. Here, we track the evolution of our current understanding of peptidoglycan and underpinning technical and methodological developments. The origin and function of chemical diversity is discussed with respect to some well-studied example species. We then explore how this chemistry is manifested in elegant and complex peptidoglycan organization and how this is interpreted in different and sometimes controversial architectural models. We contend that emerging technology brings about the possibility of achieving a complete understanding of peptidoglycan chemistry, through architecture, to the way in which diverse species and populations of cells meet the challenges of maintaining viability and growth within their environmental niches, by exploiting the bioengineering versatility of peptidoglycan.
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Affiliation(s)
- Robert D Turner
- The Krebs Institute, Department of Molecular Biology and Biotechnology, Firth Court, Western Bank, The University of Sheffield, Sheffield, S10 2TN, UK
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33
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Tocheva EI, López-Garrido J, Hughes HV, Fredlund J, Kuru E, Vannieuwenhze MS, Brun YV, Pogliano K, Jensen GJ. Peptidoglycan transformations during Bacillus subtilis sporulation. Mol Microbiol 2013; 88:673-86. [PMID: 23531131 DOI: 10.1111/mmi.12201] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/04/2013] [Indexed: 11/28/2022]
Abstract
While vegetative Bacillus subtilis cells and mature spores are both surrounded by a thick layer of peptidoglycan (PG, a polymer of glycan strands cross-linked by peptide bridges), it has remained unclear whether PG surrounds prespores during engulfment. To clarify this issue, we generated a slender ΔponA mutant that enabled high-resolution electron cryotomographic imaging. Three-dimensional reconstructions of whole cells in near-native states revealed a thin PG-like layer extending from the lateral cell wall around the prespore throughout engulfment. Cryotomography of purified sacculi and fluorescent labelling of PG in live cells confirmed that PG surrounds the prespore. The presence of PG throughout engulfment suggests new roles for PG in sporulation, including a new model for how PG synthesis might drive engulfment, and obviates the need to synthesize a PG layer de novo during cortex formation. In addition, it reveals that B. subtilis can synthesize thin, Gram-negative-like PG layers as well as its thick, archetypal Gram-positive cell wall. The continuous transformations from thick to thin and back to thick during sporulation suggest that both forms of PG have the same basic architecture (circumferential). Endopeptidase activity may be the main switch that governs whether a thin or a thick PG layer is assembled.
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Affiliation(s)
- Elitza I Tocheva
- Division of Biology, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA
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34
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Balomenou S, Fouet A, Tzanodaskalaki M, Couture-Tosi E, Bouriotis V, Boneca IG. Distinct functions of polysaccharide deacetylases in cell shape, neutral polysaccharide synthesis and virulence ofBacillus anthracis. Mol Microbiol 2013; 87:867-83. [DOI: 10.1111/mmi.12137] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/18/2012] [Indexed: 11/27/2022]
Affiliation(s)
| | | | - Mary Tzanodaskalaki
- Institute of Molecular Biology and Biotechnology; 70013; Heraklion; Crete; Greece
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35
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Heeg D, Burns DA, Cartman ST, Minton NP. Spores of Clostridium difficile clinical isolates display a diverse germination response to bile salts. PLoS One 2012; 7:e32381. [PMID: 22384234 PMCID: PMC3285209 DOI: 10.1371/journal.pone.0032381] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2011] [Accepted: 01/27/2012] [Indexed: 01/05/2023] Open
Abstract
Clostridium difficile spores play a pivotal role in the transmission of infectious diarrhoea, but in order to cause disease spores must complete germination and return to vegetative cell growth. While the mechanisms of spore germination are well understood in Bacillus, knowledge of C. difficile germination remains limited. Previous studies have shown that bile salts and amino acids play an important role in regulating the germination response of C. difficile spores. Taurocholate, in combination with glycine, can stimulate germination, whereas chenodeoxycholate has been shown to inhibit spore germination in a C. difficile clinical isolate. Our recent studies of C. difficile sporulation characteristics have since pointed to substantial diversity among different clinical isolates. Consequently, in this study we investigated how the germination characteristics of different C. difficile isolates vary in response to bile salts. By analysing 29 isolates, including 16 belonging to the BI/NAP1/027 type, we show that considerable diversity exists in both the rate and extent of C. difficile germination in response to rich medium containing both taurocholate and glycine. Strikingly, we also show that although a potent inhibitor of germination for some isolates, chenodeoxycholate does not inhibit the germination, or outgrowth, of all C. difficile strains. Finally, we provide evidence that components of rich media may induce the germination of C. difficile spores, even in the absence of taurocholate. Taken together, these data suggest that the mechanisms of C. difficile spore germination in response to bile salts are complex and require further study. Furthermore, we stress the importance of studying multiple isolates in the future when analysing the nutrients or chemicals that either stimulate or inhibit C. difficile spore germination.
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Affiliation(s)
| | | | | | - Nigel P. Minton
- Clostridia Research Group, School of Molecular Medical Sciences, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, United Kingdom
- * E-mail:
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36
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Lambert EA, Sherry N, Popham DL. In vitro and in vivo analyses of the Bacillus anthracis spore cortex lytic protein SleL. MICROBIOLOGY-SGM 2012; 158:1359-1368. [PMID: 22343356 DOI: 10.1099/mic.0.056630-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The bacterial endospore is the most resilient biological structure known. Multiple protective integument layers shield the spore core and promote spore dehydration and dormancy. Dormancy is broken when a spore germinates and becomes a metabolically active vegetative cell. Germination requires the breakdown of a modified layer of peptidoglycan (PG) known as the spore cortex. This study reports in vitro and in vivo analyses of the Bacillus anthracis SleL protein. SleL is a spore cortex lytic enzyme composed of three conserved domains: two N-terminal LysM domains and a C-terminal glycosyl hydrolase family 18 domain. Derivatives of SleL containing both, one or no LysM domains were purified and characterized. SleL is incapable of digesting intact cortical PG of either decoated spores or purified spore sacculi. However, SleL derivatives can hydrolyse fragmented PG substrates containing muramic-δ-lactam recognition determinants. The muropeptides that result from SleL hydrolysis are the products of N-acetylglucosaminidase activity. These muropeptide products are small and readily released from the cortex matrix. Loss of the LysM domain(s) decreases both PG binding and hydrolysis activity but these domains do not appear to determine specificity for muramic-δ-lactam. When the SleL derivatives are expressed in vivo, those proteins lacking one or both LysM domains do not associate with the spore. Instead, these proteins remain in the mother cell and are apparently degraded. SleL with both LysM domains localizes to the coat or cortex of the endospore. The information revealed by elucidating the role of SleL and its domains in B. anthracis sporulation and germination is important in designing new spore decontamination methods. By exploiting germination-specific lytic enzymes, eradication techniques may be greatly simplified.
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Affiliation(s)
- Emily A Lambert
- Department of Biological Sciences, Virginia Tech., Life Sciences I-MC0910, Blacksburg, VA 24061, USA
| | - Nora Sherry
- Department of Biological Sciences, Virginia Tech., Life Sciences I-MC0910, Blacksburg, VA 24061, USA
| | - David L Popham
- Department of Biological Sciences, Virginia Tech., Life Sciences I-MC0910, Blacksburg, VA 24061, USA
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37
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Tocheva EI, Matson EG, Morris DM, Moussavi F, Leadbetter JR, Jensen GJ. Peptidoglycan remodeling and conversion of an inner membrane into an outer membrane during sporulation. Cell 2011; 146:799-812. [PMID: 21884938 DOI: 10.1016/j.cell.2011.07.029] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Revised: 05/25/2011] [Accepted: 07/09/2011] [Indexed: 12/21/2022]
Abstract
Two hallmarks of the Firmicute phylum, which includes the Bacilli and Clostridia classes, are their ability to form endospores and their "Gram-positive" single-membraned, thick-cell-wall envelope structure. Acetonema longum is part of a lesser-known family (the Veillonellaceae) of Clostridia that form endospores but that are surprisingly "Gram negative," possessing both an inner and outer membrane and a thin cell wall. Here, we present macromolecular resolution, 3D electron cryotomographic images of vegetative, sporulating, and germinating A. longum cells showing that during the sporulation process, the inner membrane of the mother cell is inverted and transformed to become the outer membrane of the germinating cell. Peptidoglycan persists throughout, leading to a revised, "continuous" model of its role in the process. Coupled with genomic analyses, these results point to sporulation as a mechanism by which the bacterial outer membrane may have arisen and A. longum as a potential "missing link" between single- and double-membraned bacteria.
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Affiliation(s)
- Elitza I Tocheva
- Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA
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38
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Abstract
Molecular-genetic and muropeptide analysis techniques have been applied to examine the function in vivo of the Bacillus megaterium QM B1551 SleB and SleL proteins. In common with Bacillus subtilis and Bacillus anthracis, the presence of anhydromuropeptides in B. megaterium germination exudates, which is indicative of lytic transglycosylase activity, is associated with an intact sleB structural gene. B. megaterium sleB cwlJ double mutant strains complemented with engineered SleB variants in which the predicted N- or C-terminal domain has been deleted (SleB-ΔN or SleB-ΔC) efficiently initiate and hydrolyze the cortex, generating anhydromuropeptides in the process. Additionally, sleB cwlJ strains complemented with SleB-ΔN or SleB-ΔC, in which glutamate and aspartate residues have individually been changed to alanine, all retain the ability to hydrolyze the cortex to various degrees during germination, with concomitant release of anhydromuropeptides to the surrounding medium. These data indicate that while the presence of either the N- or C-terminal domain of B. megaterium SleB is sufficient for initiation of cortex hydrolysis and the generation of anhydromuropeptides, the perceived lytic transglycosylase activity may be derived from an enzyme(s), perhaps exclusively or in addition to SleB, which has yet to be identified. B. megaterium SleL appears to be associated with the epimerase-type activity observed previously in B. subtilis, differing from the glucosaminidase function that is apparent in B. cereus/B. anthracis.
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Hyyryläinen HL, Marciniak BC, Dahncke K, Pietiäinen M, Courtin P, Vitikainen M, Seppala R, Otto A, Becher D, Chapot-Chartier MP, Kuipers OP, Kontinen VP. Penicillin-binding protein folding is dependent on the PrsA peptidyl-prolyl cis-trans isomerase in Bacillus subtilis. Mol Microbiol 2010; 77:108-27. [PMID: 20487272 DOI: 10.1111/j.1365-2958.2010.07188.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Summary The PrsA protein is a membrane-anchored peptidyl-prolyl cis-trans isomerase in Bacillus subtilis and most other Gram-positive bacteria. It catalyses the post-translocational folding of exported proteins and is essential for normal growth of B. subtilis. We studied the mechanism behind this indispensability. We could construct a viable prsA null mutant in the presence of a high concentration of magnesium. Various changes in cell morphology in the absence of PrsA suggested that PrsA is involved in the biosynthesis of the cylindrical lateral wall. Consistently, four penicillin-binding proteins (PBP2a, PBP2b, PBP3 and PBP4) were unstable in the absence of PrsA, while muropeptide analysis revealed a 2% decrease in the peptidoglycan cross-linkage index. Misfolded PBP2a was detected in PrsA-depleted cells, indicating that PrsA is required for the folding of this PBP either directly or indirectly. Furthermore, strongly increased uniform staining of cell wall with a fluorescent vancomycin was observed in the absence of PrsA. We also demonstrated that PrsA is a dimeric or oligomeric protein which is localized at distinct spots organized in a helical pattern along the cell membrane. These results suggest that PrsA is essential for normal growth most probably as PBP folding is dependent on this PPIase.
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Affiliation(s)
- Hanne-Leena Hyyryläinen
- Antimicrobial Resistance Unit, Department of Infectious Disease Surveillance and Control, National Institute for Health and Welfare (THL), P.O. Box 30, FI-00271 Helsinki, Finland
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Clostridial spore germination versus bacilli: genome mining and current insights. Food Microbiol 2010; 28:266-74. [PMID: 21315983 DOI: 10.1016/j.fm.2010.03.016] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Revised: 03/24/2010] [Accepted: 03/25/2010] [Indexed: 11/23/2022]
Abstract
Bacilli and clostridia share the characteristic of forming metabolically inactive endospores. Spores are highly resistant to adverse environmental conditions including heat, and their ubiquitous presence in nature makes them inevitable contaminants of foods and food ingredients. Spores can germinate under favourable conditions, and the following outgrowth can lead to food spoilage and foodborne illness. Germination of spores has been best studied in Bacillus species, but the process of spore germination is less well understood in anaerobic clostridia. This paper describes a genome mining approach focusing on the genes related to spore germination of clostridia. To this end, 12 representative sequenced Bacillus genomes and 24 Clostridium genomes were analyzed for the distribution of known and putative germination-related genes and their homologues. Overall, the number of ger operons encoding germinant receptors is lower in clostridia than in bacilli, and some Clostridium species are predicted to produce cortex-lytic enzymes that are different from the ones encountered in bacilli. The in silico germination model constructed for clostridia was linked to recently obtained experimental data for selected germination determinants, mainly in Clostridium perfringens. Similarities and differences between germination mechanisms of bacilli and clostridia will be discussed.
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Contributions of four cortex lytic enzymes to germination of Bacillus anthracis spores. J Bacteriol 2009; 192:763-70. [PMID: 19966006 DOI: 10.1128/jb.01380-09] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Bacterial spores remain dormant and highly resistant to environmental stress until they germinate. Completion of germination requires the degradation of spore cortex peptidoglycan by germination-specific lytic enzymes (GSLEs). Bacillus anthracis has four GSLEs: CwlJ1, CwlJ2, SleB, and SleL. In this study, the cooperative action of all four GSLEs in vivo was investigated by combining in-frame deletion mutations to generate all possible double, triple, and quadruple GSLE mutant strains. Analyses of mutant strains during spore germination and outgrowth combined observations of optical density loss, colony-producing ability, and quantitative identification of spore cortex fragments. The lytic transglycosylase SleB alone can facilitate enough digestion to allow full spore viability and generates a variety of small and large cortex fragments. CwlJ1 is also sufficient to allow completion of nutrient-triggered germination independently and is a major factor in Ca(2+)-dipicolinic acid (DPA)-triggered germination, but its enzymatic activity remains unidentified because its products are large and not readily released from the spore's integuments. CwlJ2 contributes the least to overall cortex digestion but plays a subsidiary role in Ca(2+)-DPA-induced germination. SleL is an N-acetylglucosaminidase that plays the major role in hydrolyzing the large products of other GSLEs into small, rapidly released muropeptides. As the roles of these enzymes in cortex degradation become clearer, they will be targets for methods to stimulate premature germination of B. anthracis spores, greatly simplifying decontamination measures.
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Liu Y, Carlsson Möller M, Petersen L, Söderberg CAG, Hederstedt L. Penicillin-binding protein SpoVD disulphide is a target for StoA in Bacillus subtilis forespores. Mol Microbiol 2009; 75:46-60. [PMID: 19919673 DOI: 10.1111/j.1365-2958.2009.06964.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bacterial endospore is a dormant and heat-resistant form of life. StoA (SpoIVH) in Bacillus subtilis is a membrane-bound thioredoxin-like protein involved in endospore cortex synthesis. It is proposed to reduce disulphide bonds in hitherto unknown proteins in the intermembrane compartment of developing forespores. Starting with a bioinformatic analysis combined with mutant studies we identified the sporulation-specific, high-molecular-weight, class B penicillin-binding protein SpoVD as a putative target for StoA. We then demonstrate that SpoVD is a membrane-bound protein with two exposed redox-active cysteine residues. Structural modelling of SpoVD, based on the well characterized orthologue PBP2x of Streptococcus pneumoniae, confirmed that a disulphide bond can form close to the active site of the penicillin-binding domain restricting access of enzyme substrate or functional association with other cortex biogenic proteins. Finally, by exploiting combinations of mutations in the spoVD, stoA and ccdA genes in B. subtilis cells, we present strong in vivo evidence that supports the conclusion that StoA functions to specifically break the disulphide bond in the SpoVD protein in the forespore envelope. The findings contribute to our understanding of endospore biogenesis and open a new angle to regulation of cell wall synthesis and penicillin-binding protein activity.
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Affiliation(s)
- Yiming Liu
- Department of Cell & Organism Biology, Lund University, Lund, Sweden
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43
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SleC is essential for cortex peptidoglycan hydrolysis during germination of spores of the pathogenic bacterium Clostridium perfringens. J Bacteriol 2009; 191:2711-20. [PMID: 19218389 DOI: 10.1128/jb.01832-08] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Clostridial spore germination requires degradation of the spore's peptidoglycan (PG) cortex by cortex-lytic enzymes (CLEs), and two Clostridium perfringens CLEs, SleC and SleM, degrade cortex PG in vitro. We now find that only SleC is essential for cortex hydrolysis and viability of C. perfringens spores. C. perfringens sleC spores did not germinate completely with nutrients, KCl, or a 1:1 chelate of Ca(2+) and dipicolinic acid (Ca-DPA), and the colony-forming efficiency of sleC spores was 10(3)-fold lower than that of wild-type spores. However, sleC spores incubated with various germinants released most of their DPA, although slower than wild-type or sleM spores, and DPA release from sleC sleM spores was very slow. In contrast, germination and viability of sleM spores were similar to that of wild-type spores, although sleC sleM spores had 10(5)-fold-lower viability. These results allow the following conclusions about C. perfringens spore germination: (i) SleC is essential for cortex hydrolysis; (ii) although SleM can degrade cortex PG in vitro, this enzyme is not essential; (iii) action of SleC alone or with SleM can accelerate DPA release; and (iv) Ca-DPA does not trigger spore germination by activation of CLEs.
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Shared catalysis in virus entry and bacterial cell wall depolymerization. J Mol Biol 2009; 387:607-18. [PMID: 19361422 DOI: 10.1016/j.jmb.2009.02.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2008] [Revised: 01/31/2009] [Accepted: 02/02/2009] [Indexed: 11/23/2022]
Abstract
Bacterial virus entry and cell wall depolymerization require the breakdown of peptidoglycan (PG), the peptide-cross-linked polysaccharide matrix that surrounds bacterial cells. Structural studies of lysostaphin, a PG lytic enzyme (autolysin), have suggested that residues in the active site facilitate hydrolysis, but a clear mechanism for this reaction has remained unsolved. The active-site residues and a structural pattern of beta-sheets are conserved among lysostaphin homologs (such as LytM of Staphylococcus aureus) and the C-terminal domain of gene product 13 (gp13), a protein at the tail tip of the Bacillus subtilis bacteriophage varphi29. gp13 activity on PG and muropeptides was assayed using high-performance liquid chromatography, and gp13 was found to be a d,d-endopeptidase that cleaved the peptide cross-link. Computational modeling of the B. subtilis cross-linked peptide into the gp13 active site suggested that Asp195 may facilitate scissile-bond activation and that His247 is oriented to mediate nucleophile generation. To our knowledge, this is the first model of a Zn(2)(+) metallopeptidase and its substrate. Residue Asp195 of gp13 was found to be critical for Zn(2)(+) binding and catalysis by substitution mutagenesis with Ala or Cys. Circular dichroism and particle-induced X-ray emission spectroscopy showed that the general protein folding and Zn(2)(+) binding were maintained in the Cys mutant but reduced in the Ala mutant. These findings together support a model in which the Asp195 and His247 in gp13 and homologous residues in the LytM and lysostaphin active sites facilitate hydrolysis of the peptide substrate that cross-links PG. Thus, these autolysins and phage-entry enzymes have a shared chemical mechanism of action.
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Orsburn B, Sucre K, Popham DL, Melville SB. The SpmA/B and DacF proteins ofClostridium perfringensplay important roles in spore heat resistance. FEMS Microbiol Lett 2009; 291:188-94. [DOI: 10.1111/j.1574-6968.2008.01454.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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The Bacillus anthracis SleL (YaaH) protein is an N-acetylglucosaminidase involved in spore cortex depolymerization. J Bacteriol 2008; 190:7601-7. [PMID: 18835992 DOI: 10.1128/jb.01054-08] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Bacillus anthracis spores, the infectious agents of anthrax, are notoriously difficult to remove from contaminated areas because they are resistant to many eradication methods. These resistance properties are due to the spore's dehydration and dormancy and to the multiple protective layers surrounding the spore core, one of which is the cortex. In order for B. anthracis spores to germinate and resume growth, the cortex peptidoglycan must be depolymerized. This study reports on analyses of sleL (yaaH), which encodes a cortex-lytic enzyme. The inactivation of sleL does not affect vegetative growth, spore viability, or the initial stages of germination, including dipicolinic acid release. However, mutant spores exhibit a slight delay in the loss of optical density compared to that of wild-type spores. Mutants also retain more diaminopimelic acid and N-acetylmuramic acid during germination than wild-type spores, suggesting that the cortex peptidoglycan is not being hydrolyzed as rapidly. This finding is supported by high-pressure liquid chromatography analysis of the peptidoglycan structure used to confirm that SleL acts as an N-acetylglucosaminidase. When sleL is inactivated, the cortex peptidoglycan is not depolymerized into small muropeptides but instead is retained within the spore as large fragments. In the absence of the sleL-encoded N-acetylglucosaminidase, other cortex-lytic enzymes break down the cortex peptidoglycan sufficiently to allow rapid germination and outgrowth.
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Xu XL, Lee RTH, Fang HM, Wang YM, Li R, Zou H, Zhu Y, Wang Y. Bacterial peptidoglycan triggers Candida albicans hyphal growth by directly activating the adenylyl cyclase Cyr1p. Cell Host Microbe 2008; 4:28-39. [PMID: 18621008 DOI: 10.1016/j.chom.2008.05.014] [Citation(s) in RCA: 195] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Revised: 03/19/2008] [Accepted: 05/01/2008] [Indexed: 01/01/2023]
Abstract
Human serum potently induces hyphal development of the polymorphic fungal pathogen Candida albicans, a phenotype that contributes critically to infections. The fungal adenylyl cyclase Cyr1p is a key component of the cAMP/PKA-signaling pathway that controls diverse infection-related traits, including hyphal morphogenesis. However, identity of the serum hyphal inducer(s) and its fungal sensor remain unknown. Our initial analyses of active serum fractions revealed signs of bacterial peptidoglycan (PGN)-like molecules. Here, we show that several purified and synthetic muramyl dipeptides (MDPs), subunits of PGN, can strongly promote C. albicans hyphal growth. Analogous to PGN recognition by the mammalian sensors Nod1 and Nod2 through their leucine-rich-repeat (LRR) domain, we show that MDPs activate Cyr1p by directly binding to its LRR domain. Given the abundance of PGN in the intestine, a natural habitat and invasion site for C. albicans, our findings have important implications for the mechanisms of infection by this pathogen.
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Affiliation(s)
- Xiao-Li Xu
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A( *)STAR), 61 Biopolis Drive, Proteos, Singapore 138673
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Crystal and cryoEM structural studies of a cell wall degrading enzyme in the bacteriophage phi29 tail. Proc Natl Acad Sci U S A 2008; 105:9552-7. [PMID: 18606992 DOI: 10.1073/pnas.0803787105] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The small bacteriophage phi29 must penetrate the approximately 250-A thick external peptidoglycan cell wall and cell membrane of the Gram-positive Bacillus subtilis, before ejecting its dsDNA genome through its tail into the bacterial cytoplasm. The tail of bacteriophage phi29 is noncontractile and approximately 380 A long. A 1.8-A resolution crystal structure of gene product 13 (gp13) shows that this tail protein has spatially well separated N- and C-terminal domains, whose structures resemble lysozyme-like enzymes and metallo-endopeptidases, respectively. CryoEM reconstructions of the WT bacteriophage and mutant bacteriophages missing some or most of gp13 shows that this enzyme is located at the distal end of the phi29 tail knob. This finding suggests that gp13 functions as a tail-associated, peptidoglycan-degrading enzyme able to cleave both the polysaccharide backbone and peptide cross-links of the peptidoglycan cell wall. Comparisons of the gp13(-) mutants with the phi29 mature and emptied phage structures suggest the sequence of events that occur during the penetration of the tail through the peptidoglycan layer.
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49
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Orsburn B, Melville SB, Popham DL. Factors contributing to heat resistance of Clostridium perfringens endospores. Appl Environ Microbiol 2008; 74:3328-35. [PMID: 18378644 PMCID: PMC2423036 DOI: 10.1128/aem.02629-07] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2007] [Accepted: 03/23/2008] [Indexed: 11/20/2022] Open
Abstract
The endospores formed by strains of type A Clostridium perfringens that produce the C. perfringens enterotoxin (CPE) are known to be more resistant to heat and cold than strains that do not produce this toxin. The high heat resistance of these spores allows them to survive the cooking process, leading to a large number of food-poisoning cases each year. The relative importance of factors contributing to the establishment of heat resistance in this species is currently unknown. The present study examines the spores formed by both CPE(+) and CPE(-) strains for factors known to affect heat resistance in other species. We have found that the concentrations of DPA and metal ions, the size of the spore core, and the protoplast-to-sporoplast ratio are determining factors affecting heat resistance in these strains. While the overall thickness of the spore peptidoglycan was found to be consistent in all strains, the relative amounts of cortex and germ cell wall peptidoglycan also appear to play a role in the heat resistance of these strains.
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Affiliation(s)
- Benjamin Orsburn
- Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
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Cortex peptidoglycan lytic activity in germinating Bacillus anthracis spores. J Bacteriol 2008; 190:4541-8. [PMID: 18456807 DOI: 10.1128/jb.00249-08] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacterial endospore dormancy and resistance properties depend on the relative dehydration of the spore core, which is maintained by the spore membrane and its surrounding cortex peptidoglycan wall. During spore germination, the cortex peptidoglycan is rapidly hydrolyzed by lytic enzymes packaged into the dormant spore. The peptidoglycan structures in both dormant and germinating Bacillus anthracis Sterne spores were analyzed. The B. anthracis dormant spore peptidoglycan was similar to that found in other species. During germination, B. anthracis released peptidoglycan fragments into the surrounding medium more quickly than some other species. A major lytic enzymatic activity was a glucosaminidase, probably YaaH, that cleaved between N-acetylglucosamine and muramic-delta-lactam. An epimerase activity previously proposed to function on spore peptidoglycan was not detected, and it is proposed that glucosaminidase products were previously misidentified as epimerase products. Spore cortex lytic enzymes and their regulators are attractive targets for development of germination inhibitors to kill spores and for development of activators to cause loss of resistance properties for decontamination of spore release sites.
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