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Ramos-Silva P, Serrano M, Henriques AO. From Root to Tips: Sporulation Evolution and Specialization in Bacillus subtilis and the Intestinal Pathogen Clostridioides difficile. Mol Biol Evol 2020; 36:2714-2736. [PMID: 31350897 PMCID: PMC6878958 DOI: 10.1093/molbev/msz175] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Bacteria of the Firmicutes phylum are able to enter a developmental pathway that culminates with the formation of highly resistant, dormant endospores. Endospores allow environmental persistence, dissemination and for pathogens, are also infection vehicles. In both the model Bacillus subtilis, an aerobic organism, and in the intestinal pathogen Clostridioides difficile, an obligate anaerobe, sporulation mobilizes hundreds of genes. Their expression is coordinated between the forespore and the mother cell, the two cells that participate in the process, and is kept in close register with the course of morphogenesis. The evolutionary mechanisms by which sporulation emerged and evolved in these two species, and more broadly across Firmicutes, remain largely unknown. Here, we trace the origin and evolution of sporulation using the genes known to be involved in the process in B. subtilis and C. difficile, and estimating their gain-loss dynamics in a comprehensive bacterial macroevolutionary framework. We show that sporulation evolution was driven by two major gene gain events, the first at the base of the Firmicutes and the second at the base of the B. subtilis group and within the Peptostreptococcaceae family, which includes C. difficile. We also show that early and late sporulation regulons have been coevolving and that sporulation genes entail greater innovation in B. subtilis with many Bacilli lineage-restricted genes. In contrast, C. difficile more often recruits new sporulation genes by horizontal gene transfer, which reflects both its highly mobile genome, the complexity of the gut microbiota, and an adjustment of sporulation to the gut ecosystem.
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Affiliation(s)
- Paula Ramos-Silva
- Instituto Gulbenkian de Ciência, Oeiras, Portugal.,Marine Biodiversity Group, Naturalis Biodiversity Center, Leiden, The Netherlands
| | - Mónica Serrano
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
| | - Adriano O Henriques
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
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2
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Mearls EB, Jackter J, Colquhoun JM, Farmer V, Matthews AJ, Murphy LS, Fenton C, Camp AH. Transcription and translation of the sigG gene is tuned for proper execution of the switch from early to late gene expression in the developing Bacillus subtilis spore. PLoS Genet 2018; 14:e1007350. [PMID: 29702640 PMCID: PMC5942855 DOI: 10.1371/journal.pgen.1007350] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 05/09/2018] [Accepted: 04/03/2018] [Indexed: 12/01/2022] Open
Abstract
A cascade of alternative sigma factors directs developmental gene expression during spore formation by the bacterium Bacillus subtilis. As the spore develops, a tightly regulated switch occurs in which the early-acting sigma factor σF is replaced by the late-acting sigma factor σG. The gene encoding σG (sigG) is transcribed by σF and by σG itself in an autoregulatory loop; yet σG activity is not detected until σF-dependent gene expression is complete. This separation in σF and σG activities has been suggested to be due at least in part to a poorly understood intercellular checkpoint pathway that delays sigG expression by σF. Here we report the results of a careful examination of sigG expression during sporulation. Unexpectedly, our findings argue against the existence of a regulatory mechanism to delay sigG transcription by σF and instead support a model in which sigG is transcribed by σF with normal timing, but at levels that are very low. This low-level expression of sigG is the consequence of several intrinsic features of the sigG regulatory and coding sequence—promoter spacing, secondary structure potential of the mRNA, and start codon identity—that dampen its transcription and translation. Especially notable is the presence of a conserved hairpin in the 5’ leader sequence of the sigG mRNA that occludes the ribosome-binding site, reducing translation by up to 4-fold. Finally, we demonstrate that misexpression of sigG from regulatory and coding sequences lacking these features triggers premature σG activity in the forespore during sporulation, as well as inappropriate σG activity during vegetative growth. Altogether, these data indicate that transcription and translation of the sigG gene is tuned to prevent vegetative expression of σG and to ensure the precise timing of the switch from σF to σG in the developing spore. Global changes in gene expression occur during normal cellular growth and development, as well as during cancer cell transformation and bacterial pathogenesis. In this study we have investigated the molecular mechanisms that drive the switch from early to late developmental gene expression during spore formation by the model bacterium Bacillus subtilis. At early times, gene expression in the developing spore is directed by the transcription factor σF; at later times σF is replaced by σG. An important, yet poorly understood aspect of this σF-to-σG transition is how σG activation is delayed until the early, σF-directed phase of gene expression is complete. Here we have carefully examined expression of the gene encoding σG, sigG, and found that its transcription and translation are ordinarily dampened by several features of its regulatory and coding sequences. Moreover, we have found that this “tuning” of sigG expression is required for proper timing of the switch to σG. These results reframe our understanding of how sigG is regulated during B. subtilis sporulation and, more broadly, advance our understanding of how global changes in gene expression can be precisely executed at the molecular/genetic level.
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MESH Headings
- Bacillus subtilis/genetics
- Bacillus subtilis/physiology
- Bacterial Proteins/biosynthesis
- Bacterial Proteins/genetics
- Gene Expression Regulation, Bacterial
- Genes, Bacterial
- Inverted Repeat Sequences
- Models, Genetic
- Nucleic Acid Conformation
- Promoter Regions, Genetic
- Protein Biosynthesis
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Messenger/chemistry
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Sigma Factor/biosynthesis
- Sigma Factor/genetics
- Signal Transduction
- Spores, Bacterial/genetics
- Spores, Bacterial/physiology
- Transcription, Genetic
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Affiliation(s)
- Elizabeth B. Mearls
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
| | - Jacquelin Jackter
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
| | | | - Veronica Farmer
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
| | - Allison J. Matthews
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
| | - Laura S. Murphy
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
| | - Colleen Fenton
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
| | - Amy H. Camp
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
- * E-mail:
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3
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Martínez-Lumbreras S, Alfano C, Evans NJ, Collins KM, Flanagan KA, Atkinson RA, Krysztofinska EM, Vydyanath A, Jackter J, Fixon-Owoo S, Camp AH, Isaacson RL. Structural and Functional Insights into Bacillus subtilis Sigma Factor Inhibitor, CsfB. Structure 2018; 26:640-648.e5. [PMID: 29526435 PMCID: PMC5890618 DOI: 10.1016/j.str.2018.02.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 11/17/2017] [Accepted: 02/06/2018] [Indexed: 11/23/2022]
Abstract
Global changes in bacterial gene expression can be orchestrated by the coordinated activation/deactivation of alternative sigma (σ) factor subunits of RNA polymerase. Sigma factors themselves are regulated in myriad ways, including via anti-sigma factors. Here, we have determined the solution structure of anti-sigma factor CsfB, responsible for inhibition of two alternative sigma factors, σG and σE, during spore formation by Bacillus subtilis. CsfB assembles into a symmetrical homodimer, with each monomer bound to a single Zn2+ ion via a treble-clef zinc finger fold. Directed mutagenesis indicates that dimer formation is critical for CsfB-mediated inhibition of both σG and σE, and we have characterized these interactions in vitro. This work represents an advance in our understanding of how CsfB mediates inhibition of two alternative sigma factors to drive developmental gene expression in a bacterium.
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MESH Headings
- Amino Acid Sequence
- Bacillus subtilis/chemistry
- Bacillus subtilis/genetics
- Bacillus subtilis/metabolism
- Binding Sites
- Cations, Divalent
- Cloning, Molecular
- Crystallography, X-Ray
- Escherichia coli/genetics
- Escherichia coli/metabolism
- Gene Expression Regulation, Bacterial
- Genetic Vectors/chemistry
- Genetic Vectors/metabolism
- Models, Molecular
- Mutation
- Protein Binding
- Protein Conformation, alpha-Helical
- Protein Conformation, beta-Strand
- Protein Interaction Domains and Motifs
- Protein Isoforms/antagonists & inhibitors
- Protein Isoforms/chemistry
- Protein Isoforms/genetics
- Protein Isoforms/metabolism
- Protein Multimerization
- Recombinant Proteins/chemistry
- Recombinant Proteins/genetics
- Recombinant Proteins/metabolism
- Repressor Proteins/chemistry
- Repressor Proteins/genetics
- Repressor Proteins/metabolism
- Sequence Alignment
- Sequence Homology, Amino Acid
- Sigma Factor/antagonists & inhibitors
- Sigma Factor/chemistry
- Sigma Factor/genetics
- Sigma Factor/metabolism
- Spores, Bacterial/chemistry
- Spores, Bacterial/genetics
- Spores, Bacterial/metabolism
- Zinc/chemistry
- Zinc/metabolism
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Affiliation(s)
| | - Caterina Alfano
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK; Structural Biology and Biophysics Unit, Fondazione Ri.MED, Via Bandiera, 11, 90133 Palermo, Italy
| | - Nicola J Evans
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK
| | - Katherine M Collins
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK
| | - Kelly A Flanagan
- Department of Biological Sciences, Mount Holyoke College, 50 College Street, South Hadley, MA 01075, USA
| | - R Andrew Atkinson
- Centre for Biomolecular Spectroscopy and Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, Guy's Campus, London SE1 1UL, UK
| | - Ewelina M Krysztofinska
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK
| | - Anupama Vydyanath
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK
| | - Jacquelin Jackter
- Department of Biological Sciences, Mount Holyoke College, 50 College Street, South Hadley, MA 01075, USA
| | - Sarah Fixon-Owoo
- Department of Biological Sciences, Mount Holyoke College, 50 College Street, South Hadley, MA 01075, USA
| | - Amy H Camp
- Department of Biological Sciences, Mount Holyoke College, 50 College Street, South Hadley, MA 01075, USA
| | - Rivka L Isaacson
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK.
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4
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Wang Erickson AF, Deighan P, Chen S, Barrasso K, Garcia CP, Martínez-Lumbreras S, Alfano C, Krysztofinska EM, Thapaliya A, Camp AH, Isaacson RL, Hochschild A, Losick R. A novel RNA polymerase-binding protein that interacts with a sigma-factor docking site. Mol Microbiol 2017; 105:652-662. [PMID: 28598017 PMCID: PMC5558796 DOI: 10.1111/mmi.13724] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/06/2017] [Indexed: 11/30/2022]
Abstract
Sporulation in Bacillus subtilis is governed by a cascade of alternative RNA polymerase sigma factors. We previously identified a small protein Fin that is produced under the control of the sporulation sigma factor σF to create a negative feedback loop that inhibits σF -directed gene transcription. Cells deleted for fin are defective for spore formation and exhibit increased levels of σF -directed gene transcription. Based on pull-down experiments, chemical crosslinking, bacterial two-hybrid experiments and nuclear magnetic resonance chemical shift analysis, we now report that Fin binds to RNA polymerase and specifically to the coiled-coil region of the β' subunit. The coiled-coil is a docking site for sigma factors on RNA polymerase, and evidence is presented that the binding of Fin and σF to RNA polymerase is mutually exclusive. We propose that Fin functions by a mechanism distinct from that of classic sigma factor antagonists (anti-σ factors), which bind directly to a target sigma factor to prevent its association with RNA polymerase, and instead functions to inhibit σF by competing for binding to the β' coiled-coil.
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Affiliation(s)
- Anna F. Wang Erickson
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138
| | - Padraig Deighan
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115
- Department of Biology, Emmanuel College, 400 The Fenway, Boston, MA 02115
| | - Shanshan Chen
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138
| | - Kelsey Barrasso
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115
- Department of Biology, Emmanuel College, 400 The Fenway, Boston, MA 02115
| | - Cinthia P. Garcia
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115
- Department of Biology, Emmanuel College, 400 The Fenway, Boston, MA 02115
| | | | - Caterina Alfano
- Department of Chemistry, King's College London, Britannia House, Trinity Street, London, United Kingdom
| | - Ewelina M. Krysztofinska
- Department of Chemistry, King's College London, Britannia House, Trinity Street, London, United Kingdom
| | - Arjun Thapaliya
- Department of Chemistry, King's College London, Britannia House, Trinity Street, London, United Kingdom
| | - Amy H. Camp
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075
| | - Rivka L. Isaacson
- Department of Chemistry, King's College London, Britannia House, Trinity Street, London, United Kingdom
| | - Ann Hochschild
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115
| | - Richard Losick
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138
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5
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A Membrane-Embedded Amino Acid Couples the SpoIIQ Channel Protein to Anti-Sigma Factor Transcriptional Repression during Bacillus subtilis Sporulation. J Bacteriol 2016; 198:1451-63. [PMID: 26929302 DOI: 10.1128/jb.00958-15] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Accepted: 02/22/2016] [Indexed: 01/19/2023] Open
Abstract
UNLABELLED SpoIIQ is an essential component of a channel connecting the developing forespore to the adjacent mother cell during Bacillus subtilis sporulation. This channel is generally required for late gene expression in the forespore, including that directed by the late-acting sigma factor σ(G) Here, we present evidence that SpoIIQ also participates in a previously unknown gene regulatory circuit that specifically represses expression of the gene encoding the anti-sigma factor CsfB, a potent inhibitor of σ(G) The csfB gene is ordinarily transcribed in the forespore only by the early-acting sigma factor σ(F) However, in a mutant lacking the highly conserved SpoIIQ transmembrane amino acid Tyr-28, csfB was also aberrantly transcribed later by σ(G), the very target of CsfB inhibition. This regulation of csfB by SpoIIQ Tyr-28 is specific, given that the expression of other σ(F)-dependent genes was unaffected. Moreover, we identified a conserved element within the csfB promoter region that is both necessary and sufficient for SpoIIQ Tyr-28-mediated inhibition. These results indicate that SpoIIQ is a bifunctional protein that not only generally promotes σ(G)activity in the forespore as a channel component but also specifically maximizes σ(G)activity as part of a gene regulatory circuit that represses σ(G)-dependent expression of its own inhibitor, CsfB. Finally, we demonstrate that SpoIIQ Tyr-28 is required for the proper localization and stability of the SpoIIE phosphatase, raising the possibility that these two multifunctional proteins cooperate to fine-tune developmental gene expression in the forespore at late times. IMPORTANCE Cellular development is orchestrated by gene regulatory networks that activate or repress developmental genes at the right time and place. Late gene expression in the developing Bacillus subtilis spore is directed by the alternative sigma factor σ(G) The activity of σ(G)requires a channel apparatus through which the adjacent mother cell provides substrates that generally support gene expression. Here we report that the channel protein SpoIIQ also specifically maximizes σ(G)activity as part of a previously unknown regulatory circuit that prevents σ(G)from activating transcription of the gene encoding its own inhibitor, the anti-sigma factor CsfB. The discovery of this regulatory circuit significantly expands our understanding of the gene regulatory network controlling late gene expression in the developing B. subtilis spore.
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6
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Oppenheimer-Shaanan Y, Sibony-Nevo O, Bloom-Ackermann Z, Suissa R, Steinberg N, Kartvelishvily E, Brumfeld V, Kolodkin-Gal I. Spatio-temporal assembly of functional mineral scaffolds within microbial biofilms. NPJ Biofilms Microbiomes 2016; 2:15031. [PMID: 28721240 PMCID: PMC5515261 DOI: 10.1038/npjbiofilms.2015.31] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2015] [Revised: 10/22/2015] [Accepted: 12/15/2015] [Indexed: 11/08/2022] Open
Abstract
Historically, multicellular bacterial communities, known as biofilms, have been thought to be held together solely by a self-produced extracellular matrix. Our study identified a novel mechanism maintaining Bacillus subtilis and Mycobacterium smegmatis biofilms-active production of calcite minerals. We studied, for the first time, the effects of mutants defective in biomineralization and calcite formation on biofilm development, resilience and morphology. We demonstrated that an intrinsic rise in carbon dioxide levels within the biofilm is a strong trigger for the initiation of calcite-dependent patterning. The calcite-dependent patterns provide resistance to environmental insults and increase the overall fitness of the microbial community. Our results suggest that it is highly feasible that the formation of mineral scaffolds plays a cardinal and conserved role in bacterial multicellularity.
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Affiliation(s)
| | - Odelia Sibony-Nevo
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | | | - Ronit Suissa
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Nitai Steinberg
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Elena Kartvelishvily
- Department of Chemical Research Support, Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel
| | - Vlad Brumfeld
- Department of Chemical Research Support, Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel
| | - Ilana Kolodkin-Gal
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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7
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Fimlaid KA, Shen A. Diverse mechanisms regulate sporulation sigma factor activity in the Firmicutes. Curr Opin Microbiol 2015; 24:88-95. [PMID: 25646759 DOI: 10.1016/j.mib.2015.01.006] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2014] [Revised: 12/23/2014] [Accepted: 01/10/2015] [Indexed: 11/27/2022]
Abstract
Sporulation allows bacteria to survive adverse conditions and is essential to the lifecycle of some obligate anaerobes. In Bacillus subtilis, the sporulation-specific sigma factors, σ(F), σ(E), σ(G), and σ(K), activate compartment-specific transcriptional programs that drive sporulation through its morphological stages. The regulation of these sigma factors was predicted to be conserved across the Firmicutes, since the regulatory proteins controlling their activation are largely conserved. However, recent studies in (Pepto)Clostridium difficile, Clostridium acetobutylicum, Clostridium perfringens, and Clostridium botulinum have revealed striking differences in the order, activation, and function of sporulation sigma factors. These studies indicate that gene conservation does not necessarily predict gene function and that new mechanisms for controlling cell fate determination remain to be discovered in the anaerobic Clostridia.
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Affiliation(s)
- Kelly A Fimlaid
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA; Cellular, Molecular and Biomedical Sciences Program, University of Vermont, Burlington, VT 05405, USA
| | - Aimee Shen
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA.
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8
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Ramírez-Guadiana FH, Del Carmen Barajas-Ornelas R, Ayala-García VM, Yasbin RE, Robleto E, Pedraza-Reyes M. Transcriptional coupling of DNA repair in sporulating Bacillus subtilis cells. Mol Microbiol 2013; 90:1088-99. [PMID: 24118570 DOI: 10.1111/mmi.12417] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/29/2013] [Indexed: 11/28/2022]
Abstract
In conditions of halted or limited genome replication, like those experienced in sporulating cells of Bacillus subtilis, a more immediate detriment caused by DNA damage is altering the transcriptional programme that drives this developmental process. Here, we report that mfd, which encodes a conserved bacterial protein that mediates transcription-coupled DNA repair (TCR), is expressed together with uvrA in both compartments of B. subtilis sporangia. The function of Mfd was found to be important for processing the genetic damage during B. subtilis sporulation. Disruption of mfd sensitized developing spores to mitomycin-C (M-C) treatment and UV-C irradiation. Interestingly, in non-growing sporulating cells, Mfd played an anti-mutagenic role as its absence promoted UV-induced mutagenesis through a pathway involving YqjH/YqjW-mediated translesion synthesis (TLS). Two observations supported the participation of Mfd-dependent TCR in spore morphogenesis: (i) disruption of mfd notoriously affected the efficiency of B. subtilis sporulation and (ii) in comparison with the wild-type strain, a significant proportion of Mfd-deficient sporangia that survived UV-C treatment developed an asporogenous phenotype. We propose that the Mfd-dependent repair pathway operates during B. subtilis sporulation and that its function is required to eliminate genetic damage from transcriptionally active genes.
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9
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Coupling of σG activation to completion of engulfment during sporulation of Bacillus subtilis survives large perturbations to DNA translocation and replication. J Bacteriol 2012; 194:6264-71. [PMID: 22984259 DOI: 10.1128/jb.01470-12] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Spore formation in Bacillus subtilis is characterized by activation of RNA polymerase sigma factors, including the late-expressed σ(G). During spore formation an asymmetric division occurs, yielding the smaller prespore and the larger mother cell. At division, only 30% of the chromosome is in the prespore, and the rest is then translocated into the prespore. Following completion of engulfment of the prespore by the mother cell, σ(G) is activated in the prespore. Here we tested the link between engulfment and σ(G) activation by perturbing DNA translocation and replication, which are completed before engulfment. One approach was to have large DNA insertions in the chromosome; the second was to have an impaired DNA translocase; the third was to use a strain in which the site of termination of chromosome replication was relocated. Insertion of 2.3 Mb of Synechocystis DNA into the B. subtilis genome had the largest effect, delaying engulfment by at least 90 min. Chromosome translocation was also delayed and was completed shortly before the completion of engulfment. Despite the delay, σ(G) became active only after the completion of engulfment. All results are consistent with a strong link between completion of engulfment and σ(G) activation. They support a link between completion of chromosome translocation and completion of engulfment.
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10
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Serrano M, Real G, Santos J, Carneiro J, Moran CP, Henriques AO. A negative feedback loop that limits the ectopic activation of a cell type-specific sporulation sigma factor of Bacillus subtilis. PLoS Genet 2011; 7:e1002220. [PMID: 21935351 PMCID: PMC3174212 DOI: 10.1371/journal.pgen.1002220] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Accepted: 06/18/2011] [Indexed: 11/18/2022] Open
Abstract
Two highly similar RNA polymerase sigma subunits, σF and σG, govern the early and late phases of forespore-specific gene expression during spore differentiation in Bacillus subtilis. σF drives synthesis of σG but the latter only becomes active once engulfment of the forespore by the mother cell is completed, its levels rising quickly due to a positive feedback loop. The mechanisms that prevent premature or ectopic activation of σG while discriminating between σF and σG in the forespore are not fully comprehended. Here, we report that the substitution of an asparagine by a glutamic acid at position 45 of σG (N45E) strongly reduced binding by a previously characterized anti-sigma factor, CsfB (also known as Gin), in vitro, and increased the activity of σG in vivo. The N45E mutation caused the appearance of a sub-population of pre-divisional cells with strong activity of σG. CsfB is normally produced in the forespore, under σF control, but sigGN45E mutant cells also expressed csfB and did so in a σG-dependent manner, autonomously from σF. Thus, a negative feedback loop involving CsfB counteracts the positive feedback loop resulting from ectopic σG activity. N45 is invariant in the homologous position of σG orthologues, whereas its functional equivalent in σF proteins, E39, is highly conserved. While CsfB does not bind to wild-type σF, a E39N substitution in σF resulted in efficient binding of CsfB to σF. Moreover, under certain conditions, the E39N alteration strongly restrains the activity of σF in vivo, in a csfB-dependent manner, and the efficiency of sporulation. Therefore, a single amino residue, N45/E39, is sufficient for the ability of CsfB to discriminate between the two forespore-specific sigma factors in B. subtilis. Positive auto-regulation of a transcriptional activator during cell differentiation or development often allows the rapid and robust deployment of cell- and stage-specific genes and the routing of the differentiating cell down a specific path. Positive auto-regulation however, raises the potential for inappropriate activity of the transcription factor. Here we unravel the role of a previously characterized anti-sigma factor, CsfB, in a negative feedback loop that prevents ectopic expression of the sporulation-specific sigma factor σG of Bacillus subtilis. σG is activated in the forespore, one of the two chambers of the developing cell, at an intermediate stage in spore development. Once active, a positive feedback loop allows the rapid accumulation of σG. Synthesis of both σG and CsfB is under the control of the early forespore regulator σF, and CsfB may help prevent the premature activity of σG in the forespore. However, CsfB is also produced under σG control in non-sporulating cells, setting a negative feedback loop that we show limits its ectopic activation. We further show that an asparagine residue conserved among σG orthologues is critical for binding and inhibition by CsfB, whereas the exclusion of asparagine from the homologous position in σF confers immunity to CsfB.
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Affiliation(s)
- Mónica Serrano
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
| | - Gonçalo Real
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
| | - Joana Santos
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
| | | | - Charles P. Moran
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Adriano O. Henriques
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
- * E-mail:
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11
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Hobbs EC, Fontaine F, Yin X, Storz G. An expanding universe of small proteins. Curr Opin Microbiol 2011; 14:167-73. [PMID: 21342783 PMCID: PMC3079058 DOI: 10.1016/j.mib.2011.01.007] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Accepted: 01/28/2011] [Indexed: 01/04/2023]
Abstract
Historically, small proteins (sproteins) of less than 50 amino acids, in their final processed forms or genetically encoded as such, have been understudied. However, both serendipity and more recent focused efforts have led to the identification of a number of new sproteins in both Gram-negative and Gram-positive bacteria. Increasing evidence demonstrates that sproteins participate in a wide array of cellular processes and exhibit great diversity in their mechanisms of action, yet general principles of sprotein function are emerging. This review highlights examples of sproteins that participate in cell signaling, act as antibiotics and toxins, and serve as structural proteins. We also describe roles for sproteins in detecting and altering membrane features, acting as chaperones, and regulating the functions of larger proteins.
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Affiliation(s)
| | | | - Xuefeng Yin
- School of Basic Medical Sciences, Peking University, 100191 Beijing, China
| | - Gisela Storz
- Corresponding author address of corresponding author:
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