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Zheng Q. What are we missing in teaching the Luria-Delbrück experiment? JOURNAL OF MICROBIOLOGY & BIOLOGY EDUCATION 2024; 25:e0016123. [PMID: 38661409 PMCID: PMC11044624 DOI: 10.1128/jmbe.00161-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Accepted: 11/30/2023] [Indexed: 04/26/2024]
Abstract
The importance of teaching the Luria-Delbrück experiment to biology students is increasingly recognized by educators, and improved pedagogical methods for teaching the classic experiment have been proposed and tested in the classroom. However, there are still obstacles that impede the proper teaching of the classic experiment. This note proposes two strategies to further improve the teaching of the classic experiment. The first strategy is to be frank with an inherent limitation of the classic experiment, and instructors should explain from a logical point of view why the classic experiment cannot be used to refute the possibility of directed mutation. The second strategy is to emphasize the pioneering work of Delbrück on developing the mutant distribution that enables researchers to estimate microbial mutation rates using data generated by fluctuation experiments, and instructors should shift their attention to the overlooked essential role of the mutant distribution.
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Affiliation(s)
- Qi Zheng
- Department of Epidemiology and Biostatistics, Texas A&M School of Public Health, College Station, Texas, USA
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2
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Del Duca S, Vassallo A, Semenzato G, Fani R. Mimicking the last step of gene elongation: hints from the bacterial hisF gene. Gene 2023:147533. [PMID: 37279865 DOI: 10.1016/j.gene.2023.147533] [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: 02/23/2023] [Revised: 05/05/2023] [Accepted: 05/31/2023] [Indexed: 06/08/2023]
Abstract
Gene elongation consists in an in-tandem duplication of a gene and divergence and fusion of the two copies, resulting in a gene constituted by two divergent paralogous modules. Many present-day proteins show internal repeats of amino acid sequences, generated by gene elongation events; however, gene elongation is still a poorly studied evolutionary molecular mechanism. The most documented case is that of the histidine biosynthetic genes hisA and hisF, which derive from the gene elongation of an ancestral gene half the size of the extant ones. The aim of this work was to experimentally simulate the possible last step of the gene elongation event occurred during hisF gene evolution under selective pressure conditions. Azospirillum brasilense hisF gene, carrying a single nucleotide mutation that generates a stop codon between the two halves of the gene, was used to transform the histidine-auxotrophic Escherichia coli strain FB182 (hisF892). The transformed strain was subjected to selective pressure (i.e., low concentration/absence of histidine in the growth medium) and the obtained mutants were characterized. The restoration of prototrophy was strongly dependent on the time of incubation and on the strength of the selective pressure. The mutations involved the introduced stop codon with a single base substitution and none of the mutants restored the wild-type codon. Possible correlations between the different mutations and i) E. coli codon usage, ii) three-dimensional structures of the mutated HisF proteins, and iii) growth ability of the mutants were investigated. On the contrary, when the experiment was repeated by mutating a more conserved codon, only a synonymous substitution was obtained. Thus, experiments performed in this study allowed to mimic a possible gene elongation event occurred during the evolution of hisF gene, evidencing the ability of bacterial cells to modify their genome in short times under selective conditions.
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Affiliation(s)
- Sara Del Duca
- Department of Biology, University of Florence, Via Madonna del Piano 6, 50019, Sesto Fiorentino (FI), Italy; Research Centre for Agriculture and Environment, Council for Agricultural Research and Economics (CREA-AA), Via di Lanciola 12/A, 50125, Cascine del Riccio (FI), Italy
| | - Alberto Vassallo
- School of Biosciences and Veterinary Medicine, University of Camerino, Via Gentile III Da Varano 1, 62032, Camerino (MC) Italy
| | - Giulia Semenzato
- Department of Biology, University of Florence, Via Madonna del Piano 6, 50019, Sesto Fiorentino (FI), Italy
| | - Renato Fani
- Department of Biology, University of Florence, Via Madonna del Piano 6, 50019, Sesto Fiorentino (FI), Italy.
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3
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Herrmann JA, Koprowska A, Winters TJ, Villanueva N, Nikityuk VD, Pek F, Reis EM, Dominguez CZ, Davis D, McPherson E, Rocco SR, Recendez C, Difuntorum SM, Faeth K, Lopez MD, Awwad HM, Ghobashy RA, Cappiello L, Neidle EL, Quiñones-Soto S, Reams AB. Gene amplification mutations originate prior to selective stress in Acinetobacter baylyi. G3 (BETHESDA, MD.) 2023; 13:jkac327. [PMID: 36504387 PMCID: PMC9997567 DOI: 10.1093/g3journal/jkac327] [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: 08/23/2022] [Revised: 08/23/2022] [Accepted: 12/06/2022] [Indexed: 12/14/2022]
Abstract
The controversial theory of adaptive amplification states gene amplification mutations are induced by selective environments where they are enriched due to the stress caused by growth restriction on unadapted cells. We tested this theory with three independent assays using an Acinetobacter baylyi model system that exclusively selects for cat gene amplification mutants. Our results demonstrate all cat gene amplification mutant colonies arise through a multistep process. While the late steps occur during selection exposure, these mutants derive from low-level amplification mutant cells that form before growth-inhibiting selection is imposed. During selection, these partial mutants undergo multiple secondary steps generating higher amplification over several days to multiple weeks to eventually form visible high-copy amplification colonies. Based on these findings, amplification in this Acinetobacter system can be explained by a natural selection process that does not require a stress response. These findings have fundamental implications to understanding the role of growth-limiting selective environments on cancer development. We suggest duplication mutations encompassing growth factor genes may serve as new genomic biomarkers to facilitate early cancer detection and treatment, before high-copy amplification is attained.
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Affiliation(s)
- Jennifer A Herrmann
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Agata Koprowska
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Tesa J Winters
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Nancy Villanueva
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Victoria D Nikityuk
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Feini Pek
- Department of Mathematics and Statistics, California State University, Sacramento, CA 95819-6051, USA
| | - Elizabeth M Reis
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Constancia Z Dominguez
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Daniel Davis
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Eric McPherson
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Staci R Rocco
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Cynthia Recendez
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Shyla M Difuntorum
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Kelly Faeth
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Mario D Lopez
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Habeeba M Awwad
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Rola A Ghobashy
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Lauren Cappiello
- Department of Mathematics and Statistics, California State University, Sacramento, CA 95819-6051, USA
| | - Ellen L Neidle
- Department of Microbiology, University of Georgia, Athens, GA 30602-2605, USA
| | - Semarhy Quiñones-Soto
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
| | - Andrew B Reams
- Department of Biological Sciences, California State University, Sacramento, CA 95819-6077, USA
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4
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Effect of Non-Lethal Selection on Spontaneous Revertants of Frameshift Mutations: The Escherichia coli hisF Case. Microorganisms 2022; 10:microorganisms10040692. [PMID: 35456744 PMCID: PMC9032791 DOI: 10.3390/microorganisms10040692] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/10/2022] [Accepted: 03/18/2022] [Indexed: 01/25/2023] Open
Abstract
Microorganisms possess the potential to adapt to fluctuations in environmental parameters, and their evolution is driven by the continuous generation of mutations. The reversion of auxotrophic mutations has been widely studied; however, little is known about the reversion of frameshift mutations resulting in amino acid auxotrophy and on the structure and functioning of the protein encoded by the revertant mutated gene. The aims of this work were to analyze the appearance of reverse mutations over time and under different selective pressures and to investigate revertant enzymes' three-dimensional structures and their correlation with a different growth ability. Escherichia coli FB182 strain, carrying the hisF892 single nucleotide deletion resulting in histidine auxotrophy, was subjected to different selective pressures, and revertant mutants were isolated and characterized. The obtained results allowed us to identify different indels of different lengths located in different positions in the hisF gene, and relations with the incubation time and the selective pressure applied were observed. Moreover, the structure of the different mutant proteins was consistent with the respective revertant ability to grow in absence of histidine, highlighting a correlation between the mutations and the catalytic activity of the mutated HisF enzyme.
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Baquero F, Martínez JL, F. Lanza V, Rodríguez-Beltrán J, Galán JC, San Millán A, Cantón R, Coque TM. Evolutionary Pathways and Trajectories in Antibiotic Resistance. Clin Microbiol Rev 2021; 34:e0005019. [PMID: 34190572 PMCID: PMC8404696 DOI: 10.1128/cmr.00050-19] [Citation(s) in RCA: 66] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Evolution is the hallmark of life. Descriptions of the evolution of microorganisms have provided a wealth of information, but knowledge regarding "what happened" has precluded a deeper understanding of "how" evolution has proceeded, as in the case of antimicrobial resistance. The difficulty in answering the "how" question lies in the multihierarchical dimensions of evolutionary processes, nested in complex networks, encompassing all units of selection, from genes to communities and ecosystems. At the simplest ontological level (as resistance genes), evolution proceeds by random (mutation and drift) and directional (natural selection) processes; however, sequential pathways of adaptive variation can occasionally be observed, and under fixed circumstances (particular fitness landscapes), evolution is predictable. At the highest level (such as that of plasmids, clones, species, microbiotas), the systems' degrees of freedom increase dramatically, related to the variable dispersal, fragmentation, relatedness, or coalescence of bacterial populations, depending on heterogeneous and changing niches and selective gradients in complex environments. Evolutionary trajectories of antibiotic resistance find their way in these changing landscapes subjected to random variations, becoming highly entropic and therefore unpredictable. However, experimental, phylogenetic, and ecogenetic analyses reveal preferential frequented paths (highways) where antibiotic resistance flows and propagates, allowing some understanding of evolutionary dynamics, modeling and designing interventions. Studies on antibiotic resistance have an applied aspect in improving individual health, One Health, and Global Health, as well as an academic value for understanding evolution. Most importantly, they have a heuristic significance as a model to reduce the negative influence of anthropogenic effects on the environment.
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Affiliation(s)
- F. Baquero
- Department of Microbiology, Ramón y Cajal University Hospital, Ramón y Cajal Institute for Health Research (IRYCIS), Network Center for Research in Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - J. L. Martínez
- National Center for Biotechnology (CNB-CSIC), Madrid, Spain
| | - V. F. Lanza
- Department of Microbiology, Ramón y Cajal University Hospital, Ramón y Cajal Institute for Health Research (IRYCIS), Network Center for Research in Epidemiology and Public Health (CIBERESP), Madrid, Spain
- Central Bioinformatics Unit, Ramón y Cajal Institute for Health Research (IRYCIS), Madrid, Spain
| | - J. Rodríguez-Beltrán
- Department of Microbiology, Ramón y Cajal University Hospital, Ramón y Cajal Institute for Health Research (IRYCIS), Network Center for Research in Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - J. C. Galán
- Department of Microbiology, Ramón y Cajal University Hospital, Ramón y Cajal Institute for Health Research (IRYCIS), Network Center for Research in Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - A. San Millán
- National Center for Biotechnology (CNB-CSIC), Madrid, Spain
| | - R. Cantón
- Department of Microbiology, Ramón y Cajal University Hospital, Ramón y Cajal Institute for Health Research (IRYCIS), Network Center for Research in Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - T. M. Coque
- Department of Microbiology, Ramón y Cajal University Hospital, Ramón y Cajal Institute for Health Research (IRYCIS), Network Center for Research in Epidemiology and Public Health (CIBERESP), Madrid, Spain
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6
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Neves HI, Machado GT, Ramos TCDS, Yang HM, Yagil E, Spira B. Competition for nutritional resources masks the true frequency of bacterial mutants. BMC Biol 2020; 18:194. [PMID: 33317515 PMCID: PMC7737367 DOI: 10.1186/s12915-020-00913-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Accepted: 11/03/2020] [Indexed: 12/02/2022] Open
Abstract
Background It is widely assumed that all mutant microorganisms present in a culture are able to grow and form colonies, provided that they express the features required for selection. Unlike wild-type Escherichia coli, PHO-constitutive mutants overexpress alkaline phosphatase and hence can hydrolyze glycerol-2-phosphate (G2P) to glycerol and form colonies on plates having G2P as the sole carbon source. These mutations mostly occur in the pst operon. However, the frequency of PHO-constitutive colonies on the G2P selective plate is exceptionally low. Results We show that the rate in which spontaneous PHO-constitutive mutations emerge is about 8.0 × 10−6/generation, a relatively high rate, but the growth of most existing mutants is inhibited by their neighboring wild-type cells. This inhibition is elicited only by non-mutant viable bacteria that can take up and metabolize glycerol formed by the mutants. Evidence indicates that the few mutants that do form colonies derive from microclusters of mutants on the selective plate. A mathematical model that describes the fate of the wild-type and mutant populations under these circumstances supports these results. Conclusion This scenario in which neither the wild-type nor the majority of the mutants are able to grow resembles an unavoidable “tragedy of the commons” case which results in the collapse of the majority of the population. Cooperation between rare adjacent mutants enables them to overcome the competition and eventually form mutant colonies. The inhibition of PHO-constitutive mutants provides an example of mutant frequency masked by orders of magnitude due to a competition between mutants and their ancestral wild-type cells. Similar “tragedy of the commons-like” cases may occur in other settings and should be taken into consideration while estimating true mutant frequencies and mutation rates. Supplementary Information The online version contains supplementary material available at (doi:10.1186/s12915-020-00913-1).
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Affiliation(s)
- Henrique Iglesias Neves
- Departamento de Microbiologia, Instituto de Ciências Biomédicas Universidade de São Paulo, São Paulo, SP, Brazil
| | - Gabriella Trombini Machado
- Departamento de Microbiologia, Instituto de Ciências Biomédicas Universidade de São Paulo, São Paulo, SP, Brazil
| | | | - Hyun Mo Yang
- Departamento de Matemática Aplicada, Instituto de Matemática, Estatística e Computação Científica, Campinas, SP, Brazil
| | - Ezra Yagil
- Departament of Biochemistry and Molecular Biology, Faculty of Life Sciences, Tel-Aviv University, Tel Aviv, Israel
| | - Beny Spira
- Departamento de Microbiologia, Instituto de Ciências Biomédicas Universidade de São Paulo, São Paulo, SP, Brazil.
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7
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A Comprehensive View of Translesion Synthesis in Escherichia coli. Microbiol Mol Biol Rev 2020; 84:84/3/e00002-20. [PMID: 32554755 DOI: 10.1128/mmbr.00002-20] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The lesion bypass pathway, translesion synthesis (TLS), exists in essentially all organisms and is considered a pathway for postreplicative gap repair and, at the same time, for lesion tolerance. As with the saying "a trip is not over until you get back home," studying TLS only at the site of the lesion is not enough to understand the whole process of TLS. Recently, a genetic study uncovered that polymerase V (Pol V), a poorly expressed Escherichia coli TLS polymerase, is not only involved in the TLS step per se but also participates in the gap-filling reaction over several hundred nucleotides. The same study revealed that in contrast, Pol IV, another highly expressed TLS polymerase, essentially stays away from the gap-filling reaction. These observations imply fundamentally different ways these polymerases are recruited to DNA in cells. While access of Pol IV appears to be governed by mass action, efficient recruitment of Pol V involves a chaperone-like action of the RecA filament. We present a model of Pol V activation: the 3' tip of the RecA filament initially stabilizes Pol V to allow stable complex formation with a sliding β-clamp, followed by the capture of the terminal RecA monomer by Pol V, thus forming a functional Pol V complex. This activation process likely determines higher accessibility of Pol V than of Pol IV to normal DNA. Finally, we discuss the biological significance of TLS polymerases during gap-filling reactions: error-prone gap-filling synthesis may contribute as a driving force for genetic diversity, adaptive mutation, and evolution.
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8
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Nguyen A, Maisnier-Patin S, Yamayoshi I, Kofoid E, Roth JR. Selective Inbreeding: Genetic Crosses Drive Apparent Adaptive Mutation in the Cairns-Foster System of Escherichia coli. Genetics 2020; 214:333-354. [PMID: 31810989 PMCID: PMC7017022 DOI: 10.1534/genetics.119.302754] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 12/02/2019] [Indexed: 01/09/2023] Open
Abstract
The Escherichia coli system of Cairns and Foster employs a lac frameshift mutation that reverts rarely (10-9/cell/division) during unrestricted growth. However, when 108 cells are plated on lactose medium, the nongrowing lawn produces ∼50 Lac+ revertant colonies that accumulate linearly with time over 5 days. Revertants carry very few associated mutations. This behavior has been attributed to an evolved mechanism ("adaptive mutation" or "stress-induced mutagenesis") that responds to starvation by preferentially creating mutations that improve growth. We describe an alternative model, "selective inbreeding," in which natural selection acts during intercellular transfer of the plasmid that carries the mutant lac allele and the dinB gene for an error-prone polymerase. Revertant genome sequences show that the plasmid is more intensely mutagenized than the chromosome. Revertants vary widely in their number of plasmid and chromosomal mutations. Plasmid mutations are distributed evenly, but chromosomal mutations are focused near the replication origin. Rare, heavily mutagenized, revertants have acquired a plasmid tra mutation that eliminates conjugation ability. These findings support the new model, in which revertants are initiated by rare pre-existing cells (105) with many copies of the F'lac plasmid. These cells divide under selection, producing daughters that mate. Recombination between donor and recipient plasmids initiates rolling-circle plasmid over-replication, causing a mutagenic elevation of DinB level. A lac+ reversion event starts chromosome replication and mutagenesis by accumulated DinB. After reversion, plasmid transfer moves the revertant lac+ allele into an unmutagenized cell, and away from associated mutations. Thus, natural selection explains why mutagenesis appears stress-induced and directed.
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Affiliation(s)
- Amanda Nguyen
- Department of Microbiology and Molecular Genetics, University of California, Davis, California 95616
| | - Sophie Maisnier-Patin
- Department of Microbiology and Molecular Genetics, University of California, Davis, California 95616
| | - Itsugo Yamayoshi
- Department of Microbiology and Molecular Genetics, University of California, Davis, California 95616
| | - Eric Kofoid
- Department of Microbiology and Molecular Genetics, University of California, Davis, California 95616
| | - John R Roth
- Department of Microbiology and Molecular Genetics, University of California, Davis, California 95616
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9
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The Role of Mutation Bias in Adaptive Evolution. Trends Ecol Evol 2019; 34:422-434. [PMID: 31003616 DOI: 10.1016/j.tree.2019.01.015] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 01/27/2019] [Accepted: 01/30/2019] [Indexed: 11/24/2022]
Abstract
Mutational input is the ultimate source of genetic variation, but mutations are not thought to affect the direction of adaptive evolution. Recently, critics of standard evolutionary theory have questioned the random and non-directional nature of mutations, claiming that the mutational process can be adaptive in its own right. We discuss here mutation bias in adaptive evolution. We find little support for mutation bias as an independent force in adaptive evolution, although it can interact with selection under conditions of small population size and when standing genetic variation is limited, entirely consistent with standard evolutionary theory. We further emphasize that natural selection can shape the phenotypic effects of mutations, giving the false impression that directed mutations are driving adaptive evolution.
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10
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Fernández‐Cabezón L, Cros A, Nikel PI. Evolutionary Approaches for Engineering Industrially Relevant Phenotypes in Bacterial Cell Factories. Biotechnol J 2019; 14:e1800439. [DOI: 10.1002/biot.201800439] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2019] [Revised: 04/08/2019] [Indexed: 12/12/2022]
Affiliation(s)
- Lorena Fernández‐Cabezón
- The Novo Nordisk Foundation Center for BiosustainabilityTechnical University of Denmark 2800 Kongens Lyngby Denmark
| | - Antonin Cros
- The Novo Nordisk Foundation Center for BiosustainabilityTechnical University of Denmark 2800 Kongens Lyngby Denmark
| | - Pablo I. Nikel
- The Novo Nordisk Foundation Center for BiosustainabilityTechnical University of Denmark 2800 Kongens Lyngby Denmark
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11
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Esnault C, Lee M, Ham C, Levin HL. Transposable element insertions in fission yeast drive adaptation to environmental stress. Genome Res 2018; 29:85-95. [PMID: 30541785 PMCID: PMC6314160 DOI: 10.1101/gr.239699.118] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Accepted: 11/15/2018] [Indexed: 01/06/2023]
Abstract
Cells are regularly exposed to a range of naturally occurring stress that can restrict growth or cause lethality. In response, cells activate expression networks with hundreds of genes that together increase resistance to common environmental insults. However, stress response networks can be insufficient to ensure survival, which raises the question of whether cells possess genetic programs that can promote adaptation to novel forms of stress. We found transposable element (TE) mobility in Schizosaccharomyces pombe was greatly increased when cells were exposed to unusual forms of stress such as heavy metals, caffeine, and the plasticizer phthalate. By subjecting TE-tagged cells to CoCl2, we found the TE integration provided the major path to resistance. Groups of insertions that provided resistance were linked to TOR regulation and metal response genes. We extended our study of adaptation by analyzing TE positions in 57 genetically distinct wild strains. The genomic positions of 1048 polymorphic LTRs were strongly associated with a range of stress response genes, indicating TE integration promotes adaptation in natural conditions. These data provide strong support for the idea, first proposed by Barbara McClintock, that TEs provide a system to modify the genome in response to stress.
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Affiliation(s)
- Caroline Esnault
- Section on Eukaryotic Transposable Elements, Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Michael Lee
- Section on Eukaryotic Transposable Elements, Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Chloe Ham
- Section on Eukaryotic Transposable Elements, Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Henry L Levin
- Section on Eukaryotic Transposable Elements, Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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12
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Selection and Plasmid Transfer Underlie Adaptive Mutation in Escherichia coli. Genetics 2018; 210:821-841. [PMID: 30194073 DOI: 10.1534/genetics.118.301347] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Accepted: 08/30/2018] [Indexed: 11/18/2022] Open
Abstract
In the Cairns-Foster adaptive mutation system, a +1 lac frameshift mutant of Escherichia coli is plated on lactose medium, where the nondividing population gives rise to Lac+ revertant colonies during a week under selection. Reversion requires the mutant lac allele to be located on a conjugative F'lac plasmid that also encodes the error-prone DNA polymerase, DinB. Rare plated cells with multiple copies of the mutant F'lac plasmid initiate the clones that develop into revertants under selection. These initiator cells arise before plating, and their extra lac copies allow them to divide on lactose and produce identical F'lac-bearing daughter cells that can mate with each other. DNA breaks can form during plasmid transfer and their recombinational repair can initiate rolling-circle replication of the recipient plasmid. This replication is mutagenic because the amplified plasmid encodes the error-prone DinB polymerase. A new model proposes that Lac+ revertants arise during mutagenic over-replication of the F'lac plasmid under selection. This mutagenesis is focused on the plasmid because the cell chromosome replicates very little. The outer membrane protein OmpA is essential for reversion under selection. OmpA helps cells conserve energy and may stabilize the long-term mating pairs that produce revertants.
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13
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Selection-Enhanced Mutagenesis of lac Genes Is Due to Their Coamplification with dinB Encoding an Error-Prone DNA Polymerase. Genetics 2018; 208:1009-1021. [PMID: 29301907 DOI: 10.1534/genetics.117.300409] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 12/27/2017] [Indexed: 11/18/2022] Open
Abstract
To test whether growth limitation induces mutations, Cairns and Foster constructed an Escherichia coli strain whose mutant lac allele provides 1-2% of normal ability to use lactose. This strain cannot grow on lactose, but produces ∼50 Lac+ revertant colonies per 108 plated cells over 5 days. About 80% of revertants carry a stable lac+ mutation made by the error-prone DinB polymerase, which may be induced during growth limitation; 10% of Lac+ revertants are stable but form without DinB; and the remaining 10% grow by amplifying their mutant lac allele and are unstably Lac+ Induced DinB mutagenesis has been explained in two ways: (1) upregulation of dinB expression in nongrowing cells ("stress-induced mutagenesis") or (2) selected local overreplication of the lac and dinB+ genes on lactose medium (selected amplification) in cells that are not dividing. Transcription of dinB is necessary but not sufficient for mutagenesis. Evidence is presented that DinB enhances reversion only when encoded somewhere on the F'lac plasmid that carries the mutant lac gene. A new model will propose that rare preexisting cells (1 in a 1000) have ∼10 copies of the F'lac plasmid, providing them with enough energy to divide, mate, and overreplicate their F'lac plasmid under selective conditions. In these clones, repeated replication of F'lac in nondividing cells directs opportunities for lac reversion and increases the copy number of the dinB+ gene. Amplification of dinB+ increases the error rate of replication and increases the number of lac+ revertants. Thus, reversion is enhanced in nondividing cells not by stress-induced mutagenesis, but by selected coamplification of the dinB and lac genes, both of which happen to lie on the F'lac plasmid.
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14
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Charlesworth D, Barton NH, Charlesworth B. The sources of adaptive variation. Proc Biol Sci 2017; 284:rspb.2016.2864. [PMID: 28566483 DOI: 10.1098/rspb.2016.2864] [Citation(s) in RCA: 101] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 05/04/2017] [Indexed: 12/16/2022] Open
Abstract
The role of natural selection in the evolution of adaptive phenotypes has undergone constant probing by evolutionary biologists, employing both theoretical and empirical approaches. As Darwin noted, natural selection can act together with other processes, including random changes in the frequencies of phenotypic differences that are not under strong selection, and changes in the environment, which may reflect evolutionary changes in the organisms themselves. As understanding of genetics developed after 1900, the new genetic discoveries were incorporated into evolutionary biology. The resulting general principles were summarized by Julian Huxley in his 1942 book Evolution: the modern synthesis Here, we examine how recent advances in genetics, developmental biology and molecular biology, including epigenetics, relate to today's understanding of the evolution of adaptations. We illustrate how careful genetic studies have repeatedly shown that apparently puzzling results in a wide diversity of organisms involve processes that are consistent with neo-Darwinism. They do not support important roles in adaptation for processes such as directed mutation or the inheritance of acquired characters, and therefore no radical revision of our understanding of the mechanism of adaptive evolution is needed.
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Affiliation(s)
- Deborah Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK
| | - Nicholas H Barton
- Institute of Science and Technology Austria, Klosterneuburg 3400, Austria
| | - Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK
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15
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Lada AG, Stepchenkova EI, Zhuk AS, Kliver SF, Rogozin IB, Polev DE, Dhar A, Pavlov YI. Recombination Is Responsible for the Increased Recovery of Drug-Resistant Mutants with Hypermutated Genomes in Resting Yeast Diploids Expressing APOBEC Deaminases. Front Genet 2017; 8:202. [PMID: 29312434 PMCID: PMC5733079 DOI: 10.3389/fgene.2017.00202] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2017] [Accepted: 11/22/2017] [Indexed: 12/11/2022] Open
Abstract
DNA editing deaminases (APOBECs) are implicated in generation of mutations in somatic cells during tumorigenesis. APOBEC-dependent mutagenesis is thought to occur during transient exposure of unprotected single-stranded DNA. Mutations frequently occur in clusters (kataegis). We investigated mechanisms of mutant generation in growing and resting diploid yeast expressing APOBEC from sea lamprey, PmCDA1, whose kataegistic effect was previously shown to be associated with transcription. We have found that the frequency of canavanine-resistant mutants kept raising after growth cessation, while the profile of transcription remained unchanged. Surprisingly, the overall number of mutations in the genomes did not elevate in resting cells. Thus, mutations were accumulated during vigorous growth stage with both intense replication and transcription. We found that the elevated recovery of can1 mutant clones in non-growing cells is the result of loss of heterozygosity (LOH) leading to clusters of homozygous mutations in the chromosomal regions distal to the reporter gene. We confirmed that recombination frequency in resting cells was elevated by orders of magnitude, suggesting that cells were transiently committed to meiotic levels of recombination, a process referred to in yeast genetics as return-to-growth. In its extreme, on day 6 of starvation, a few mutant clones were haploid, likely resulting from completed meiosis. Distribution of mutations along chromosomes indicated that PmCDA1 was active during ongoing recombination events and sometimes produced characteristic kataegis near initial breakpoints. AID and APOBEC1 behaved similar to PmCDA1. We conclude that replication, transcription, and mitotic recombination contribute to the recovered APOBEC-induced mutations in resting diploids. The mechanism is relevant to the initial stages of oncogenic transformation in terminally differentiated cells, when recombination may lead to the LOH exposing recessive mutations induced by APOBECs in cell's history and to acquisition of new mutations near original break.
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Affiliation(s)
- Artem G Lada
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, United States.,Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA, United States
| | - Elena I Stepchenkova
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, United States.,Department of Genetics and Biotechnology, Saint Petersburg State University, Saint Petersburg, Russia.,Vavilov Institute of General Genetics, Russian Academy of Sciences, Saint Petersburg, Russia
| | - Anna S Zhuk
- Department of Genetics and Biotechnology, Saint Petersburg State University, Saint Petersburg, Russia.,Vavilov Institute of General Genetics, Russian Academy of Sciences, Saint Petersburg, Russia
| | - Sergei F Kliver
- Department of Genetics and Biotechnology, Saint Petersburg State University, Saint Petersburg, Russia
| | - Igor B Rogozin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, United States.,Institute of Cytology and Genetics, Novosibirsk, Russia
| | - Dmitrii E Polev
- Research Resource Center "Biobank", Research Park, Saint-Petersburg State University, Saint Petersburg, Russia
| | - Alok Dhar
- Department of Genetics, Cell Biology and Anatomy and Vice Chancellor of Research Core, University of Nebraska Medical Center, Omaha, NE, United States
| | - Youri I Pavlov
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE, United States.,Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, United States.,Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE, United States.,Department of Genetics Cell Biology and Anatomy, University of Nebraska Medical Center, Omaha, NE, United States
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16
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Abstract
Evolutionary theory has been extended almost continually since the evolutionary synthesis (ES), but except for the much greater importance afforded genetic drift, the principal tenets of the ES have been strongly supported. Adaptations are attributable to the sorting of genetic variation by natural selection, which remains the only known cause of increase in fitness. Mutations are not adaptively directed, but as principal authors of the ES recognized, the material (structural) bases of biochemistry and development affect the variety of phenotypic variations that arise by mutation and recombination. Against this historical background, I analyse major propositions in the movement for an 'extended evolutionary synthesis'. 'Niche construction' is a new label for a wide variety of well-known phenomena, many of which have been extensively studied, but (as with every topic in evolutionary biology) some aspects may have been understudied. There is no reason to consider it a neglected 'process' of evolution. The proposition that phenotypic plasticity may engender new adaptive phenotypes that are later genetically assimilated or accommodated is theoretically plausible; it may be most likely when the new phenotype is not truly novel, but is instead a slight extension of a reaction norm already shaped by natural selection in similar environments. However, evolution in new environments often compensates for maladaptive plastic phenotypic responses. The union of population genetic theory with mechanistic understanding of developmental processes enables more complete understanding by joining ultimate and proximate causation; but the latter does not replace or invalidate the former. Newly discovered molecular phenomena have been easily accommodated in the past by elaborating orthodox evolutionary theory, and it appears that the same holds today for phenomena such as epigenetic inheritance. In several of these areas, empirical evidence is needed to evaluate enthusiastic speculation. Evolutionary theory will continue to be extended, but there is no sign that it requires emendation.
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Affiliation(s)
- Douglas J. Futuyma
- Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY, USA
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17
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Humayun MZ, Zhang Z, Butcher AM, Moshayedi A, Saier MH. Hopping into a hot seat: Role of DNA structural features on IS5-mediated gene activation and inactivation under stress. PLoS One 2017; 12:e0180156. [PMID: 28666002 PMCID: PMC5493358 DOI: 10.1371/journal.pone.0180156] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Accepted: 06/09/2017] [Indexed: 11/30/2022] Open
Abstract
Insertion sequence elements (IS elements) are proposed to play major roles in shaping the genetic and phenotypic landscapes of prokaryotic cells. Recent evidence has raised the possibility that environmental stress conditions increase IS hopping into new sites, and often such hopping has the phenotypic effect of relieving the stress. Although stress-induced targeted mutations have been reported for a number of E. coli genes, the glpFK (glycerol utilization) and the cryptic bglGFB (β-glucoside utilization) systems are among the best characterized where the effects of IS insertion-mediated gene activation are well-characterized at the molecular level. In the glpFK system, starvation of cells incapable of utilizing glycerol leads to an IS5 insertion event that activates the glpFK operon, and enables glycerol utilization. In the case of the cryptic bglGFB operon, insertion of IS5 (and other IS elements) into a specific region in the bglG upstream sequence has the effect of activating the operon in both growing cells, and in starving cells. However, a major unanswered question in the glpFK system, the bgl system, as well as other examples, has been why the insertion events are promoted at specific locations, and how the specific stress condition (glycerol starvation for example) can be mechanistically linked to enhanced insertion at a specific locus. In this paper, we show that a specific DNA structural feature (superhelical stress-induced duplex destabilization, SIDD) is associated with "stress-induced" IS5 insertion in the glpFK, bglGFB, flhDC, fucAO and nfsB systems. We propose a speculative mechanistic model that links specific environmental conditions to the unmasking of an insertional hotspot in the glpFK system. We demonstrate that experimentally altering the predicted stability of a SIDD element in the nfsB gene significantly impacts IS5 insertion at its hotspot.
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Affiliation(s)
- M. Zafri Humayun
- Department of Microbiology, Biochemistry & Molecular Genetics, Rutgers—New Jersey Medical School, Newark, NJ, United States of America
| | - Zhongge Zhang
- Department of Molecular Biology, Division of Biological Sciences, University of California San Diego, La Jolla, CA, United States of America
| | - Anna M. Butcher
- Department of Molecular Biology, Division of Biological Sciences, University of California San Diego, La Jolla, CA, United States of America
| | - Aref Moshayedi
- Department of Molecular Biology, Division of Biological Sciences, University of California San Diego, La Jolla, CA, United States of America
| | - Milton H. Saier
- Department of Molecular Biology, Division of Biological Sciences, University of California San Diego, La Jolla, CA, United States of America
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18
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Dormeyer M, Lübke AL, Müller P, Lentes S, Reuß DR, Thürmer A, Stülke J, Daniel R, Brantl S, Commichau FM. Hierarchical mutational events compensate for glutamate auxotrophy of a Bacillus subtilis gltC mutant. ENVIRONMENTAL MICROBIOLOGY REPORTS 2017; 9:279-289. [PMID: 28294562 DOI: 10.1111/1758-2229.12531] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Revised: 03/01/2017] [Accepted: 03/05/2017] [Indexed: 06/06/2023]
Abstract
Glutamate is the major donor of nitrogen for anabolic reactions. The Gram-positive soil bacterium Bacillus subtilis either utilizes exogenously provided glutamate or synthesizes it using the gltAB-encoded glutamate synthase (GOGAT). In the absence of glutamate, the transcription factor GltC activates expression of the GOGAT genes for glutamate production. Consequently, a gltC mutant strain is auxotrophic for glutamate. Using a genetic selection and screening system, we could isolate and differentiate between gltC suppressor mutants in one step. All mutants had acquired the ability to synthesize glutamate, independent of GltC. We identified (i) gain-of-function mutations in the gltR gene, encoding the transcription factor GltR, (ii) mutations in the promoter of the gltAB operon and (iii) massive amplification of the genomic locus containing the gltAB operon. The mutants belonging to the first two classes constitutively expressed the gltAB genes and produced sufficient glutamate for growth. By contrast, mutants that belong to the third class appeared most frequently and solved glutamate limitation by increasing the copy number of the poorly expressed gltAB genes. Thus, glutamate auxotrophy of a B. subtilis gltC mutant can be relieved in multiple ways. Moreover, recombination-dependent amplification of the gltAB genes is the predominant mutational event indicating a hierarchy of mutations.
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Affiliation(s)
- Miriam Dormeyer
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Anastasia L Lübke
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Peter Müller
- Department of Genetics, Bacterial Genetics, Friedrich Schiller University Jena, Philosophenweg 12, Jena, 07743, Germany
| | - Sabine Lentes
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Daniel R Reuß
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Andrea Thürmer
- Department of Genomic and Applied Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Jörg Stülke
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Rolf Daniel
- Department of Genomic and Applied Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Sabine Brantl
- Department of Genetics, Bacterial Genetics, Friedrich Schiller University Jena, Philosophenweg 12, Jena, 07743, Germany
| | - Fabian M Commichau
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
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Sekowska A, Wendel S, Fischer EC, Nørholm MHH, Danchin A. Generation of mutation hotspots in ageing bacterial colonies. Sci Rep 2016; 6:2. [PMID: 28442761 PMCID: PMC5431349 DOI: 10.1038/s41598-016-0005-4] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 08/24/2016] [Indexed: 02/08/2023] Open
Abstract
How do ageing bacterial colonies generate adaptive mutants? Over a period of two months, we isolated on ageing colonies outgrowing mutants able to use a new carbon source, and sequenced their genomes. This allowed us to uncover exquisite details on the molecular mechanism behind their adaptation: most mutations were located in just a few hotspots in the genome, and over time, mutations increasingly were consistent with the involvement of 8-oxo-guanosine, formed exclusively on the transcribed strand. This work provides strong support for retromutagenesis as a general process creating adaptive mutations during ageing.
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Zhang Z, Saier MH. Transposon-mediated activation of the Escherichia coli glpFK operon is inhibited by specific DNA-binding proteins: Implications for stress-induced transposition events. Mutat Res 2016; 793-794:22-31. [PMID: 27810619 DOI: 10.1016/j.mrfmmm.2016.10.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 08/18/2016] [Accepted: 10/22/2016] [Indexed: 11/16/2022]
Abstract
Escherichia coli cells deleted for the cyclic AMP (cAMP) receptor protein (Crp) gene (Δcrp) cannot utilize glycerol because cAMP-Crp is a required activator of the glycerol utilization operon, glpFK. We have previously shown that a transposon, Insertion Sequence 5 (IS5), can insert into the upstream regulatory region of the operon to activate the glpFK promoter and enable glycerol utilization. GlpR, which represses glpFK transcription, binds to the glpFK upstream region near the site of IS5 insertion and inhibits insertion. By adding cAMP to the culture medium in ΔcyaA cells, we here show that the cAMP-Crp complex, which also binds to the glpFK upstream regulatory region, inhibits IS5 hopping into the activating site. Control experiments showed that the frequencies of mutations in response to cAMP were independent of parental cell growth rate and the selection procedure. These findings led to the prediction that glpFK-activating IS5 insertions can also occur in wild-type (Crp+) cells under conditions that limit cAMP production. Accordingly, we found that IS5 insertion into the activating site in wild-type cells is elevated in the presence of glycerol and a non-metabolizable sugar analogue that lowers cytoplasmic cAMP concentrations. The resultant IS5 insertion mutants arising in this minimal medium become dominant constituents of the population after prolonged periods of growth. The results show that DNA binding transcription factors can reversibly mask a favored transposon target site, rendering a hot spot for insertion less favored. Such mechanisms could have evolved by natural selection to overcome environmental adversity.
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Affiliation(s)
- Zhongge Zhang
- Department of Molecular Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, United States
| | - Milton H Saier
- Department of Molecular Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, United States.
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21
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Classic Spotlight: Look, Max—No Math Required! J Bacteriol 2016; 198:2281-2. [DOI: 10.1128/jb.00525-16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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22
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Phenotypic heterogeneity in a bacteriophage population only appears as stress-induced mutagenesis. Curr Genet 2016; 62:771-773. [PMID: 27126384 DOI: 10.1007/s00294-016-0606-2] [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: 03/20/2016] [Revised: 04/17/2016] [Accepted: 04/19/2016] [Indexed: 01/30/2023]
Abstract
Stress-induced mutagenesis has been studied in cancer cells, yeast, bacteria, and archaea, but not in viruses. In a recent publication, we present a bacteriophage model showing an apparent stress-induced mutagenesis. We show that the stress does not drive the mutagenesis, but only selects the fittest mutants. The mechanism underlying the observed phenomenon is a phenotypic heterogeneity that resembles persistence of the viral population. The new findings, the background for the ongoing debate on stress-induced mutagenesis, and the phenotypic heterogeneity underlying a novel phage infection strategy are discussed in this short manuscript.
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Yosef I, Edgar R, Levy A, Amitai G, Sorek R, Munitz A, Qimron U. Natural selection underlies apparent stress-induced mutagenesis in a bacteriophage infection model. Nat Microbiol 2016; 1:16047. [DOI: 10.1038/nmicrobiol.2016.47] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 03/11/2016] [Indexed: 11/09/2022]
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Abstract
How can we stop cancer progression? Current strategies depend on modelling progression as the balanced outcome of mutations in, and expression of, tumour suppressor genes and oncogenes. New treatments emerge from successful attempts to tip that balance, but secondary mutational escape from those treatments has become a major impediment because it leads to resistance. In this Opinion article, we argue for a return to an earlier stratagem: tumour cell reversion. Treatments based on selection and analysis of stable revertants could create more durable remissions by reducing the selective pressure that leads to rapid drug resistance.
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Reinterpreting Long-Term Evolution Experiments: Is Delayed Adaptation an Example of Historical Contingency or a Consequence of Intermittent Selection? J Bacteriol 2016; 198:1009-12. [PMID: 26883821 DOI: 10.1128/jb.00110-16] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Van Hofwegen et al. demonstrated that Escherichia coli rapidly evolves the ability to use citrate when long selective periods are provided (D. J. Van Hofwegen, C. J. Hovde, and S. A. Minnich, J Bacteriol 198:1022-1034, 2016, http://dx.doi.org/10.1128/JB.00831-15). This contrasts with the extreme delay (15 years of daily transfers) seen in the long-term evolution experiments of Lenski and coworkers. Their idea of "historical contingency" may require reinterpretation. Rapid evolution seems to involve selection for duplications of the whole cit locus that are too unstable to contribute when selection is provided in short pulses.
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