1
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Iuliani I, Mbemba G, Lagomarsino MC, Sclavi B. Direct single-cell observation of a key Escherichia coli cell-cycle oscillator. SCIENCE ADVANCES 2024; 10:eado5398. [PMID: 39018394 PMCID: PMC466948 DOI: 10.1126/sciadv.ado5398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Accepted: 06/10/2024] [Indexed: 07/19/2024]
Abstract
Initiation of DNA replication in Escherichia coli is coupled to cell size via the DnaA protein, whose activity is dependent on its nucleotide-bound state. However, the oscillations in DnaA activity have never been observed at the single-cell level. By measuring the volume-specific production rate of a reporter protein under control of a DnaA-regulated promoter, we could distinguish two distinct cell-cycle oscillators. The first, driven by both DnaA activity and SeqA repression, shows a causal relationship with cell size and divisions, similarly to initiation events. The second one, a reporter of DnaA activity alone, loses the synchrony and causality properties. Our results show that transient inhibition of gene expression by SeqA keeps the oscillation of volume-sensing DnaA activity in phase with the subsequent division event and suggest that DnaA activity peaks do not correspond directly to initiation events.
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Affiliation(s)
- Ilaria Iuliani
- LBPA, UMR 8113, CNRS, ENS Paris-Saclay, 91190 Gif-sur-Yvette, France
- LCQB, UMR 7238, CNRS, Sorbonne Université, 4 Place Jussieu, 75005 Paris, France
- IFOM ETS—The AIRC Institute of Molecular Oncology, Via Adamello 16, 20139 Milan, Italy
| | - Gladys Mbemba
- LBPA, UMR 8113, CNRS, ENS Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Marco Cosentino Lagomarsino
- IFOM ETS—The AIRC Institute of Molecular Oncology, Via Adamello 16, 20139 Milan, Italy
- Dipartimento di Fisica, Università degli Studi di Milano, and I.N.F.N, Via Celoria 16, 20133 Milan, Italy
| | - Bianca Sclavi
- LCQB, UMR 7238, CNRS, Sorbonne Université, 4 Place Jussieu, 75005 Paris, France
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2
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Jane A, Rasher DB, Waller J, Annis E, Frederich M. Rearing condition influences gene expression in postlarval American lobster (Homarus americanus). PLoS One 2024; 19:e0307169. [PMID: 39024318 PMCID: PMC11257295 DOI: 10.1371/journal.pone.0307169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Accepted: 07/01/2024] [Indexed: 07/20/2024] Open
Abstract
The American lobster (Homarus americanus) is an economically important species in the western Atlantic and its climate-driven range shift northward along the east coast of the United States is well documented. The thermal tolerance of lab-reared postlarvae of this species has been extensively investigated to better understand settlement and recruitment dynamics. However, there have been few studies focused on wild-caught postlarvae, and even fewer that have analyzed lab-rearing conditions in context of diet. In this study, we investigated gene transcriptional changes in postlarvae caught in the wild, as well as postlarvae reared in the laboratory on a brine shrimp diet or a wild-sourced zooplankton diet. We found between wild-caught and brine shrimp-reared larvae 3,682 differentially expressed genes, and between wild and zooplankton-reared postlarvae 3,939 differentially expressed genes. Between the two lab-reared groups fed different diets 2,603 genes were differentially expressed. We also exposed individuals in all rearing groups to chronic temperature treatments of 8°C and 26°C and found that both temperature extremes elicit 68-95% fewer transcriptional changes in wild postlarvae compared to either lab-reared group. In wild postlarvae, we identified differential expression of transcripts within the FoxO signaling pathway, a signaling pathway with a central role in cellular physiology, as potential molecular markers for cold tolerance in the American lobster. These findings contextualize the current literature on lab-reared postlarvae as containing conservative estimates for in situ organisms and can be used to inform population distribution modeling efforts. They also provide evidence for the need to adjust lab-rearing techniques or source wild larval crustaceans to augment studies of larval biology.
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Affiliation(s)
- Aubrey Jane
- University of New England, School of Marine and Environmental Programs, Biddeford, Maine, United States of America
| | - Douglas B. Rasher
- Bigelow Laboratory for Ocean Sciences, East Boothbay, Maine, United States of America
| | - Jesica Waller
- Maine Department of Marine Resources, West Boothbay, Maine, United States of America
| | - Eric Annis
- Hood College, Frederick, Maryland, United States of America
| | - Markus Frederich
- University of New England, School of Marine and Environmental Programs, Biddeford, Maine, United States of America
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3
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Wu L, Zhang Y, Hong X, Wu M, Wang L, Yan X. Deciphering the Relationship between Cell Growth and Cell Cycle in Individual Escherichia coli Cells by Flow Cytometry. Anal Chem 2024. [PMID: 39015018 DOI: 10.1021/acs.analchem.4c02058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/18/2024]
Abstract
Accurate coordination of chromosome replication and cell division is essential for cellular processes, yet the regulatory mechanisms governing the bacterial cell cycle remain contentious. The lack of quantitative data connecting key cell cycle players at the single-cell level across large samples hinders consensus. Employing high-throughput flow cytometry, we quantitatively correlated the expression levels of key cell cycle proteins (FtsZ, MreB, and DnaA) with DNA content in individual bacteria. Our findings reveal distinct correlations depending on the chromosome number (CN), specifically whether CN ≤2 or ≥4, unveiling a mixed regulatory scenario in populations where CN of 2 or 4 coexist. We observed function-dependent regulations for these key proteins across nonoverlapping division cycles and various nutrient conditions. Notably, a logarithmic relationship between total protein content and replication origin number across nutrient conditions suggests a unified mechanism governing cell cycle progression, confirming the applicability of Schaechter's growth law to cells with CN ≥4. For the first time, we established a proportional relationship between the synthesis rates of key cell cycle proteins and chromosome dynamics in cells with CN ≥4. Drug experiments highlighted CN 2 and 4 as pivotal turning points influencing cellular resource allocation. This high-throughput, single-cell analysis provides interconnected quantitative insights into key molecular events, facilitating a predictive understanding of the relationship between cell growth and cell cycle.
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Affiliation(s)
- Lina Wu
- Department of Chemical Biology, MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, Key Laboratory for Chemical Biology of Fujian Province, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Yuzhen Zhang
- Department of Chemical Biology, MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, Key Laboratory for Chemical Biology of Fujian Province, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Xinyi Hong
- Department of Chemical Biology, MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, Key Laboratory for Chemical Biology of Fujian Province, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Mingkai Wu
- Department of Chemical Biology, MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, Key Laboratory for Chemical Biology of Fujian Province, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Liangan Wang
- Department of Chemical Biology, MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, Key Laboratory for Chemical Biology of Fujian Province, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Xiaomei Yan
- Department of Chemical Biology, MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, Key Laboratory for Chemical Biology of Fujian Province, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
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4
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Royzenblat SK, Freddolino L. Spatio-temporal organization of the E. coli chromosome from base to cellular length scales. EcoSal Plus 2024:eesp00012022. [PMID: 38864557 DOI: 10.1128/ecosalplus.esp-0001-2022] [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: 05/19/2023] [Accepted: 04/17/2024] [Indexed: 06/13/2024]
Abstract
Escherichia coli has been a vital model organism for studying chromosomal structure, thanks, in part, to its small and circular genome (4.6 million base pairs) and well-characterized biochemical pathways. Over the last several decades, we have made considerable progress in understanding the intricacies of the structure and subsequent function of the E. coli nucleoid. At the smallest scale, DNA, with no physical constraints, takes on a shape reminiscent of a randomly twisted cable, forming mostly random coils but partly affected by its stiffness. This ball-of-spaghetti-like shape forms a structure several times too large to fit into the cell. Once the physiological constraints of the cell are added, the DNA takes on overtwisted (negatively supercoiled) structures, which are shaped by an intricate interplay of many proteins carrying out essential biological processes. At shorter length scales (up to about 1 kb), nucleoid-associated proteins organize and condense the chromosome by inducing loops, bends, and forming bridges. Zooming out further and including cellular processes, topological domains are formed, which are flanked by supercoiling barriers. At the megabase-scale both large, highly self-interacting regions (macrodomains) and strong contacts between distant but co-regulated genes have been observed. At the largest scale, the nucleoid forms a helical ellipsoid. In this review, we will explore the history and recent advances that pave the way for a better understanding of E. coli chromosome organization and structure, discussing the cellular processes that drive changes in DNA shape, and what contributes to compaction and formation of dynamic structures, and in turn how bacterial chromatin affects key processes such as transcription and replication.
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Affiliation(s)
- Sonya K Royzenblat
- Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Lydia Freddolino
- Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, Michigan, USA
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, USA
- Department of Computational Medicine & Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, USA
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5
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Ludvikova L, Simon E, Deygas M, Panier T, Plamont MA, Ollion J, Tebo A, Piel M, Jullien L, Robert L, Le Saux T, Espagne A. Near-infrared co-illumination of fluorescent proteins reduces photobleaching and phototoxicity. Nat Biotechnol 2024; 42:872-876. [PMID: 37537501 PMCID: PMC11180605 DOI: 10.1038/s41587-023-01893-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 06/30/2023] [Indexed: 08/05/2023]
Abstract
Here we present a method to reduce the photobleaching of fluorescent proteins and the associated phototoxicity. It exploits a photophysical process known as reverse intersystem crossing, which we induce by near-infrared co-illumination during fluorophore excitation. This dual illumination method reduces photobleaching effects 1.5-9.2-fold, can be easily implemented on commercial microscopes and is effective in eukaryotic and prokaryotic cells with a wide range of fluorescent proteins.
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Affiliation(s)
- Lucie Ludvikova
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France
| | - Emma Simon
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France
| | - Mathieu Deygas
- Institut Curie, Paris Sciences et Lettres (PSL) Research University, Centre National de la Recherche Scientifique (CNRS), Paris, France
- Institut Pierre-Gilles de Gennes, PSL Research University, Paris, France
| | - Thomas Panier
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine (IBPS), Laboratoire Jean Perrin (LJP), Paris, France
| | - Marie-Aude Plamont
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France
| | | | - Alison Tebo
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France
| | - Matthieu Piel
- Institut Curie, Paris Sciences et Lettres (PSL) Research University, Centre National de la Recherche Scientifique (CNRS), Paris, France
- Institut Pierre-Gilles de Gennes, PSL Research University, Paris, France
| | - Ludovic Jullien
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France
| | - Lydia Robert
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine (IBPS), Laboratoire Jean Perrin (LJP), Paris, France.
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France.
| | - Thomas Le Saux
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France.
| | - Agathe Espagne
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France.
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6
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Nieto C, Vargas-García CA, Pedraza JM, Singh A. Mechanisms of cell size regulation in slow-growing Escherichia coli cells: discriminating models beyond the adder. NPJ Syst Biol Appl 2024; 10:61. [PMID: 38811603 PMCID: PMC11137094 DOI: 10.1038/s41540-024-00383-z] [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: 09/11/2023] [Accepted: 05/09/2024] [Indexed: 05/31/2024] Open
Abstract
Under ideal conditions, Escherichia coli cells divide after adding a fixed cell size, a strategy known as the adder. This concept applies to various microbes and is often explained as the division that occurs after a certain number of stages, associated with the accumulation of precursor proteins at a rate proportional to cell size. However, under poor media conditions, E. coli cells exhibit a different size regulation. They are smaller and follow a sizer-like division strategy where the added size is inversely proportional to the size at birth. We explore three potential causes for this deviation: degradation of the precursor protein and two models where the propensity for accumulation depends on the cell size: a nonlinear accumulation rate, and accumulation starting at a threshold size termed the commitment size. These models fit the mean trends but predict different distributions given the birth size. To quantify the precision of the models to explain the data, we used the Akaike information criterion and compared them to open datasets of slow-growing E. coli cells in different media. We found that none of the models alone can consistently explain the data. However, the degradation model better explains the division strategy when cells are larger, whereas size-related models (power-law and commitment size) account for smaller cells. Our methodology proposes a data-based method in which different mechanisms can be tested systematically.
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Affiliation(s)
- César Nieto
- Department of Physics, Universidad de los Andes, Bogotá, Colombia
- Department of Electrical and Computer Engineering, University of Delaware, Newark, DE, 19716, USA
| | | | | | - Abhyudai Singh
- Department of Electrical and Computer Engineering, University of Delaware, Newark, DE, 19716, USA.
- Department of Electrical and Computer Engineering, Biomedical Engineering, Mathematical Sciences, Center of Bioinformatic and Computational Biology, University of Delaware, Newark, DE, 19716, USA.
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7
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Govers SK, Campos M, Tyagi B, Laloux G, Jacobs-Wagner C. Apparent simplicity and emergent robustness in the control of the Escherichia coli cell cycle. Cell Syst 2024; 15:19-36.e5. [PMID: 38157847 DOI: 10.1016/j.cels.2023.12.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 06/15/2023] [Accepted: 12/01/2023] [Indexed: 01/03/2024]
Abstract
To examine how bacteria achieve robust cell proliferation across diverse conditions, we developed a method that quantifies 77 cell morphological, cell cycle, and growth phenotypes of a fluorescently labeled Escherichia coli strain and >800 gene deletion derivatives under multiple nutrient conditions. This approach revealed extensive phenotypic plasticity and deviating mutant phenotypes were often nutrient dependent. From this broad phenotypic landscape emerged simple and robust unifying rules (laws) that connect DNA replication initiation, nucleoid segregation, FtsZ ring formation, and cell constriction to specific aspects of cell size (volume, length, or added length) at the population level. Furthermore, completion of cell division followed the initiation of cell constriction after a constant time delay across strains and nutrient conditions, identifying cell constriction as a key control point for cell size determination. Our work provides a population-level description of the governing principles by which E. coli integrates cell cycle processes and growth rate with cell size to achieve its robust proliferative capability. A record of this paper's transparent peer review process is included in the supplemental information.
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Affiliation(s)
- Sander K Govers
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA; de Duve Institute, UCLouvain, Brussels, Belgium; Department of Biology, KU Leuven, Leuven, Belgium
| | - Manuel Campos
- Centre de Biologie Intégrative de Toulouse, Laboratoire de Microbiologie et Génétique Moléculaires, Université de Toulouse, Toulouse, France
| | - Bhavyaa Tyagi
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA; Department of Biology, Stanford University, Stanford, CA 94305, USA
| | | | - Christine Jacobs-Wagner
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA; Department of Biology, Stanford University, Stanford, CA 94305, USA; Sarafan Chemistry, Engineering Medicine for Human Health Institute, Stanford University, Stanford, CA 94305, USA; Department of Microbiology and Immunology, Stanford School of Medicine, Stanford, CA 94305, USA.
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8
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Sadhir I, Murray SM. Mid-cell migration of the chromosomal terminus is coupled to origin segregation in Escherichia coli. Nat Commun 2023; 14:7489. [PMID: 37980336 PMCID: PMC10657355 DOI: 10.1038/s41467-023-43351-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Accepted: 11/07/2023] [Indexed: 11/20/2023] Open
Abstract
Bacterial chromosomes are dynamically and spatially organised within cells. In slow-growing Escherichia coli, the chromosomal terminus is initially located at the new pole and must therefore migrate to midcell during replication to reproduce the same pattern in the daughter cells. Here, we use high-throughput time-lapse microscopy to quantify this transition, its timing and its relationship to chromosome segregation. We find that terminus centralisation is a rapid discrete event that occurs ~25 min after initial separation of duplicated origins and ~50 min before the onset of bulk nucleoid segregation but with substantial variation between cells. Despite this variation, its movement is tightly coincident with the completion of origin segregation, even in the absence of its linkage to the divisome, suggesting a coupling between these two events. Indeed, we find that terminus centralisation does not occur if origin segregation away from mid-cell is disrupted, which results in daughter cells having an inverted chromosome organisation. Overall, our study quantifies the choreography of origin-terminus positioning and identifies an unexplored connection between these loci, furthering our understanding of chromosome segregation in this bacterium.
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Affiliation(s)
- Ismath Sadhir
- Max Planck Institute for Terrestrial Microbiology and LOEWE Centre for Synthetic Microbiology (SYNMIKRO), Marburg, Germany
- Microcosm Earth Center, Max Planck Institute for Terrestrial Microbiology and Philipps-Universität Marburg, Marburg, Germany
| | - Seán M Murray
- Max Planck Institute for Terrestrial Microbiology and LOEWE Centre for Synthetic Microbiology (SYNMIKRO), Marburg, Germany.
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9
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Wang S, Chen X, Jin X, Gu F, Jiang W, Qi Q, Liang Q. Creating Polyploid Escherichia Coli and Its Application in Efficient L-Threonine Production. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2302417. [PMID: 37749873 PMCID: PMC10625114 DOI: 10.1002/advs.202302417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 07/31/2023] [Indexed: 09/27/2023]
Abstract
Prokaryotic genomes are generally organized in haploid. In synthetic biological research, efficient chassis cells must be constructed to produce bio-based products. Here, the essential division of the ftsZ gene to create functional polyploid E. coli is regulated. The artificial polyploid E. coli containing 2-4 chromosomes is confirmed through PCR amplification, terminator localization, and flow cytometry. The polyploid E. coli exhibits a larger cell size, and its low pH tolerance and acetate resistance are stronger than those of haploid E. coli. Transcriptome analysis shows that the genes of the cell's main functional pathways are significantly upregulated in the polyploid E. coli. These advantages of the polyploid E. coli results in the highest reported L-threonine yield (160.3 g L-1 ) in fed-batch fermentation to date. In summary, an easy and convenient method for constructing polyploid E. coli and demonstrated its application in L-threonine production is developed. This work provides a new approach for creating an excellent host strain for biochemical production and studying the evolution of prokaryotes and their chromosome functions.
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Affiliation(s)
- Sumeng Wang
- State Key Laboratory of Microbial TechnologyShandong UniversityQingdao266237P. R. China
| | - Xuanmu Chen
- State Key Laboratory of Microbial TechnologyShandong UniversityQingdao266237P. R. China
| | - Xin Jin
- State Key Laboratory of Microbial TechnologyShandong UniversityQingdao266237P. R. China
| | - Fei Gu
- State Key Laboratory of Microbial TechnologyShandong UniversityQingdao266237P. R. China
| | - Wei Jiang
- Research Center of Basic MedicineCentral Hospital Affiliated to Shandong First Medical UniversityJinan250013P. R. China
| | - Qingsheng Qi
- State Key Laboratory of Microbial TechnologyShandong UniversityQingdao266237P. R. China
| | - Quanfeng Liang
- State Key Laboratory of Microbial TechnologyShandong UniversityQingdao266237P. R. China
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10
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Vashistha H, Jammal-Touma J, Singh K, Rabin Y, Salman H. Bacterial cell-size changes resulting from altering the relative expression of Min proteins. Nat Commun 2023; 14:5710. [PMID: 37714867 PMCID: PMC10504268 DOI: 10.1038/s41467-023-41487-0] [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: 10/14/2022] [Accepted: 09/06/2023] [Indexed: 09/17/2023] Open
Abstract
The timing of cell division, and thus cell size in bacteria, is determined in part by the accumulation dynamics of the protein FtsZ, which forms the septal ring. FtsZ localization depends on membrane-associated Min proteins, which inhibit FtsZ binding to the cell pole membrane. Changes in the relative concentrations of Min proteins can disrupt FtsZ binding to the membrane, which in turn can delay cell division until a certain cell size is reached, in which the dynamics of Min proteins frees the cell membrane long enough to allow FtsZ ring formation. Here, we study the effect of Min proteins relative expression on the dynamics of FtsZ ring formation and cell size in individual Escherichia coli bacteria. Upon inducing overexpression of minE, cell size increases gradually to a new steady-state value. Concurrently, the time required to initiate FtsZ ring formation grows as the size approaches the new steady-state, at which point the ring formation initiates as early as before induction. These results highlight the contribution of Min proteins to cell size control, which may be partially responsible for the size fluctuations observed in bacterial populations, and may clarify how the size difference acquired during asymmetric cell division is offset.
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Affiliation(s)
- Harsh Vashistha
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT, USA
| | - Joanna Jammal-Touma
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA
| | - Kulveer Singh
- Department of Physics and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, Israel
| | - Yitzhak Rabin
- Department of Physics and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, Israel
| | - Hanna Salman
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA.
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11
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Leonard AC. Recollections of a Helmstetter Disciple. Life (Basel) 2023; 13:life13051114. [PMID: 37240759 DOI: 10.3390/life13051114] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 04/25/2023] [Accepted: 04/28/2023] [Indexed: 05/28/2023] Open
Abstract
Nearly fifty years ago, it became possible to construct E. coli minichromosomes using recombinant DNA technology. These very small replicons, comprising the unique replication origin of the chromosome oriC coupled to a drug resistance marker, provided new opportunities to study the regulation of bacterial chromosome replication, were key to obtaining the nucleotide sequence information encoded into oriC and were essential for the development of a ground-breaking in vitro replication system. However, true authenticity of the minichromosome model system required that they replicate during the cell cycle with chromosome-like timing specificity. I was fortunate enough to have the opportunity to construct E. coli minichromosomes in the laboratory of Charles Helmstetter and, for the first time, measure minichromosome cell cycle regulation. In this review, I discuss the evolution of this project along with some additional studies from that time related to the DNA topology and segregation properties of minichromosomes. Despite the significant passage of time, it is clear that large gaps in our understanding of oriC regulation still remain. I discuss some specific topics that continue to be worthy of further study.
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Affiliation(s)
- Alan C Leonard
- Department of Biological Sciences, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32952, USA
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12
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Woldringh CL. The Bacterial Nucleoid: From Electron Microscopy to Polymer Physics—A Personal Recollection. Life (Basel) 2023; 13:life13040895. [PMID: 37109423 PMCID: PMC10143432 DOI: 10.3390/life13040895] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Revised: 03/22/2023] [Accepted: 03/24/2023] [Indexed: 03/30/2023] Open
Abstract
In the 1960s, electron microscopy did not provide a clear answer regarding the compact or dispersed organization of the bacterial nucleoid. This was due to the necessary preparation steps of fixation and dehydration (for embedding) and freezing (for freeze-fracturing). Nevertheless, it was possible to measure the lengths of nucleoids in thin sections of slow-growing Escherichia coli cells, showing their gradual increase along with cell elongation. Later, through application of the so-called agar filtration method for electron microscopy, we were able to perform accurate measurements of cell size and shape. The introduction of confocal and fluorescence light microscopy enabled measurements of size and position of the bacterial nucleoid in living cells, inducing the concepts of “nucleoid occlusion” for localizing cell division and of “transertion” for the final step of nucleoid segregation. The question of why the DNA does not spread throughout the cytoplasm was approached by applying polymer-physical concepts of interactions between DNA and proteins. This gave a mechanistic insight in the depletion of proteins from the nucleoid, in accordance with its low refractive index observed by phase-contrast microscopy. Although in most bacterial species, the widely conserved proteins of the ParABS-system play a role in directing the segregation of newly replicated DNA strands, the basis for the separation and opposing movement of the chromosome arms was proposed to lie in preventing intermingling of nascent daughter strands already in the early replication bubble. E. coli, lacking the ParABS system, may be suitable for investigating this basic mechanism of DNA strand separation and segregation.
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Affiliation(s)
- Conrad L Woldringh
- Bacterial Cell Biology, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, 1098 XH Amsterdam, The Netherlands
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13
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Kar P, Tiruvadi-Krishnan S, Männik J, Männik J, Amir A. Using conditional independence tests to elucidate causal links in cell cycle regulation in Escherichia coli. Proc Natl Acad Sci U S A 2023; 120:e2214796120. [PMID: 36897981 PMCID: PMC10089181 DOI: 10.1073/pnas.2214796120] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 01/09/2023] [Indexed: 03/12/2023] Open
Abstract
How cells regulate their cell cycles is a central question for cell biology. Models of cell size homeostasis have been proposed for bacteria, archaea, yeast, plant, and mammalian cells. New experiments bring forth high volumes of data suitable for testing existing models of cell size regulation and proposing new mechanisms. In this paper, we use conditional independence tests in conjunction with data of cell size at key cell cycle events (birth, initiation of DNA replication, and constriction) in the model bacterium Escherichia coli to select between the competing cell cycle models. We find that in all growth conditions that we study, the division event is controlled by the onset of constriction at midcell. In slow growth, we corroborate a model where replication-related processes control the onset of constriction at midcell. In faster growth, we find that the onset of constriction is affected by additional cues beyond DNA replication. Finally, we also find evidence for the presence of additional cues triggering initiations of DNA replication apart from the conventional notion where the mother cells solely determine the initiation event in the daughter cells via an adder per origin model. The use of conditional independence tests is a different approach in the context of understanding cell cycle regulation and it can be used in future studies to further explore the causal links between cell events.
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Affiliation(s)
- Prathitha Kar
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA02134
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA02138
| | | | - Jaana Männik
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN37996
| | - Jaan Männik
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN37996
| | - Ariel Amir
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA02134
- Department of Complex Systems, Weizmann Institute of Science, Rehovot7610001, Israel
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Abstract
Cell division in Escherichia coli starts with the formation of an FtsZ protofilament network at midcell, the Z ring. However, only after a considerable lag period does the cell start to form a midcell constriction. The onset of constriction depends upon the arrival of so-called late divisome proteins, among which, FtsN is the last essential one. The timing and dependency of FtsN arrival to the divisome, along with genetic evidence, suggests it triggers cell division. In this study, we used high-throughput fluorescence microscopy to determine the arrival of FtsN and the early divisome protein ZapA to midcell at a single-cell level during the cell cycle. Our data show while the recruitment of ZapA/FtsZ is gradual in the cell cycle, recruitment of FtsN is rapid and begins at about the onset of constriction. At this time, the fraction of ZapA/FtsZ in the Z ring approaches its peak value. We also find a second increase in FtsN recruitment to the divisome, which begins once the amount of ZapA/FtsZ at midcell starts decreasing. Increasing hypermorphic FtsA* (FtsA R286W), but not FtsA, accelerates FtsN recruitment but not constriction. This finding is consistent with FtsA* recruiting FtsN with some other divisome component being rate-limiting for constriction under these conditions. Finally, our data support the recently proposed idea that ZapA/FtsZ and FtsN are part of physically separate complexes in midcell throughout the whole septation process. IMPORTANCE Cell division in most bacteria starts with the formation of an FtsZ protofilament network at midcell, the Z ring. However, cells only start to constrict after a considerable lag. A factor thought to trigger the onset of constriction in Escherichia coli is FtsN, which is the last essential protein to be recruited to the Z ring. Using a high-throughput quantitative fluorescence microscopy, we determine the cell cycle-dependent recruitment of FtsN to the Z ring. Our data show rapid accumulation of FtsN to the Z ring about a quarter of the cell cycle after the formation of the Z ring. This initial wave is followed by another increase in FtsN recruitment once the FtsZ protofilament network starts to disassemble. The presence of FtsA* accelerates FtsN recruitment to the Z ring but does not lead to earlier constrictions. Our data furthermore suggest FtsZ and FtsN are part of physically separate complexes throughout the division process.
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