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Wu CH, Hsu WL, Tsai CC, Chao HR, Wu CY, Chen YH, Lai YR, Chen CH, Tsai MH. 7,10,13,16-Docosatetraenoic acid impairs neurobehavioral development by increasing reactive oxidative species production in Caenorhabditis elegans. Life Sci 2023; 319:121500. [PMID: 36796717 DOI: 10.1016/j.lfs.2023.121500] [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: 06/08/2022] [Revised: 02/07/2023] [Accepted: 02/09/2023] [Indexed: 02/17/2023]
Abstract
AIMS To investigate human breast milk (HBM) lipids that may adversely affect infant neurodevelopment. MAIN METHODS We performed multivariate analyses that combined lipidomics and psychologic Bayley-III scales to identify which HBM lipids are involved in regulating infant neurodevelopment. We observed a significant moderate negative correlation between 7,10,13,16-docosatetraenoic acid (omega-6, C22H36O2, the common name adrenic acid, AdA) and adaptive behavioral development. We further studied the effects of AdA on neurodevelopment by using Caenorhabditis elegans (C. elegans) as a model. Worms from larval stages L1 to L4 were supplemented with AdA at 5 nominal concentrations (0 μM [control], 0.1 μM, 1 μM, 10 μM, and 100 μM) and subjected to behavioral and mechanistic analyses. KEY FINDINGS Supplementation with AdA from larval stages L1 to L4 impaired neurobehavioral development, such as locomotive behaviors, foraging ability, chemotaxis behavior, and aggregation behavior. Furthermore, AdA upregulated the production of intracellular reactive oxygen species. AdA-induced oxidative stress blocked serotonin synthesis and serotoninergic neuron activity and inhibited expression of daf-16 and the daf-16-regulated genes mtl-1, mtl-2, sod-1, and sod-3, resulting in attenuation of the lifespan in C. elegans. SIGNIFICANCE Our study reveals that AdA is a harmful HBM lipid that may have adverse effects on infant adaptive behavioral development. We believe this information may be critical for AdA administration guidance in children's health care.
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Affiliation(s)
- Chia-Hsiu Wu
- School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Wen-Li Hsu
- Department of Dermatology, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80145, Taiwan; Regenerative Medicine and Cell Therapy Research Center, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
| | - Ching-Chung Tsai
- Department of Pediatrics, E-Da Hospital, No. 8, Yida Rd., Kaohsiung 82445, Taiwan; School of Medicine, College of Medicine, I-Shou University, Kaohsiung 82445, Taiwan
| | - How-Ran Chao
- Department of Environmental Science and Engineering, College of Engineering, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan; Emerging Compounds Research Center, General Research Service Center, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan; Institute of Food Safety Management, College of Agriculture, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan.
| | - Ching-Ying Wu
- Department of Dermatology, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80145, Taiwan; Department of Cosmetic Science, Chang Gung University of Science and Technology, Taoyuan 33303, Taiwan.
| | - Yi-Hsuan Chen
- School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Yun-Ru Lai
- Regenerative Medicine and Cell Therapy Research Center, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Chu-Huang Chen
- Vascular and Medicinal Research, The Texas Heart Institute, Houston, TX 77030, USA; New York Heart Research Foundation, Mineola, NY 11501, USA; Institute for Biomedical Sciences, Shinshu University, Nagano 390-8621, Japan.
| | - Ming-Hsien Tsai
- Department of Child Care, College of Humanities and Social Sciences, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan; Department of Oral Hygiene, College of Dental Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
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2
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Gutiérrez R, Ram Y, Berman J, Carstens Marques de Sousa K, Nachum-Biala Y, Britzi M, Elad D, Glaser G, Covo S, Harrus S. Adaptive resistance mutations at supra-inhibitory concentrations independent of SOS mutagenesis. Mol Biol Evol 2021; 38:4095-4115. [PMID: 34175952 PMCID: PMC8476149 DOI: 10.1093/molbev/msab196] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Emergence of resistant bacteria during antimicrobial treatment is one of the most critical and universal health threats. It is known that several stress-induced mutagenesis and heteroresistance mechanisms can enhance microbial adaptation to antibiotics. Here, we demonstrate that the pathogen Bartonella can undergo stress-induced mutagenesis despite the fact it lacks error-prone polymerases, the rpoS gene and functional UV-induced mutagenesis. We demonstrate that Bartonella acquire de novo single mutations during rifampicin exposure at suprainhibitory concentrations at a much higher rate than expected from spontaneous fluctuations. This is while exhibiting a minimal heteroresistance capacity. The emerged resistant mutants acquired a single rpoB mutation, whereas no other mutations were found in their whole genome. Interestingly, the emergence of resistance in Bartonella occurred only during gradual exposure to the antibiotic, indicating that Bartonella sense and react to the changing environment. Using a mathematical model, we demonstrated that, to reproduce the experimental results, mutation rates should be transiently increased over 1,000-folds, and a larger population size or greater heteroresistance capacity is required. RNA expression analysis suggests that the increased mutation rate is due to downregulation of key DNA repair genes (mutS, mutY, and recA), associated with DNA breaks caused by massive prophage inductions. These results provide new evidence of the hazard of antibiotic overuse in medicine and agriculture.
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Affiliation(s)
- Ricardo Gutiérrez
- The Koret School of Veterinary Medicine, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel.,The Center for Research in Tropical Diseases, Faculty of Microbiology, University of Costa Rica, San José, Costa Rica
| | - Yoav Ram
- School of Zoology, Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.,School of Computer Science, Interdisciplinary Center Herzliya, Herzliya, Israel
| | - Judith Berman
- Shmunis School of Biomedicine and Cancer, Faculty of Life Sciences, Tel Aviv University, Tel Aviv University, Ramat Aviv, Israel
| | | | - Yaarit Nachum-Biala
- The Koret School of Veterinary Medicine, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Malka Britzi
- The National Residue Control Laboratory, The Kimron Veterinary Institute, Bet Dagan, Israel
| | - Daniel Elad
- Department of Clinical Bacteriology and Mycology, The Kimron Veterinary Institute, Bet Dagan, Israel
| | - Gad Glaser
- Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Shay Covo
- Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Shimon Harrus
- The Koret School of Veterinary Medicine, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel
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3
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Elez M. Mismatch Repair: From Preserving Genome Stability to Enabling Mutation Studies in Real-Time Single Cells. Cells 2021; 10:cells10061535. [PMID: 34207040 PMCID: PMC8235422 DOI: 10.3390/cells10061535] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 06/11/2021] [Accepted: 06/15/2021] [Indexed: 12/18/2022] Open
Abstract
Mismatch Repair (MMR) is an important and conserved keeper of the maintenance of genetic information. Miroslav Radman's contributions to the field of MMR are multiple and tremendous. One of the most notable was to provide, along with Bob Wagner and Matthew Meselson, the first direct evidence for the existence of the methyl-directed MMR. The purpose of this review is to outline several aspects and biological implications of MMR that his work has helped unveil, including the role of MMR during replication and recombination editing, and the current understanding of its mechanism. The review also summarizes recent discoveries related to the visualization of MMR components and discusses how it has helped shape our understanding of the coupling of mismatch recognition to replication. Finally, the author explains how visualization of MMR components has paved the way to the study of spontaneous mutations in living cells in real time.
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Affiliation(s)
- Marina Elez
- Micalis Institute, INRAE, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France;
- Laboratoire Jean Perrin (LJP), Institut de Biologie Paris-Seine (IBPS), CNRS, Sorbonne Université, F-75005 Paris, France
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4
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Mitigation of host cell mutations and regime shift during microbial fermentation: a perspective from flux memory. Curr Opin Biotechnol 2020; 66:227-235. [DOI: 10.1016/j.copbio.2020.08.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Revised: 08/01/2020] [Accepted: 08/12/2020] [Indexed: 12/19/2022]
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5
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Degeneration of industrial bacteria caused by genetic instability. World J Microbiol Biotechnol 2020; 36:119. [DOI: 10.1007/s11274-020-02901-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 07/14/2020] [Indexed: 12/11/2022]
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6
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Liu J, Lee R, Britton BM, London JA, Yang K, Hanne J, Lee JB, Fishel R. MutL sliding clamps coordinate exonuclease-independent Escherichia coli mismatch repair. Nat Commun 2019; 10:5294. [PMID: 31757945 PMCID: PMC6876574 DOI: 10.1038/s41467-019-13191-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Accepted: 10/22/2019] [Indexed: 01/09/2023] Open
Abstract
A shared paradigm of mismatch repair (MMR) across biology depicts extensive exonuclease-driven strand-specific excision that begins at a distant single-stranded DNA (ssDNA) break and proceeds back past the mismatched nucleotides. Historical reconstitution studies concluded that Escherichia coli (Ec) MMR employed EcMutS, EcMutL, EcMutH, EcUvrD, EcSSB and one of four ssDNA exonucleases to accomplish excision. Recent single-molecule images demonstrated that EcMutS and EcMutL formed cascading sliding clamps on a mismatched DNA that together assisted EcMutH in introducing ssDNA breaks at distant newly replicated GATC sites. Here we visualize the complete strand-specific excision process and find that long-lived EcMutL sliding clamps capture EcUvrD helicase near the ssDNA break, significantly increasing its unwinding processivity. EcSSB modulates the EcMutL–EcUvrD unwinding dynamics, which is rarely accompanied by extensive ssDNA exonuclease digestion. Together these observations are consistent with an exonuclease-independent MMR strand excision mechanism that relies on EcMutL–EcUvrD helicase-driven displacement of ssDNA segments between adjacent EcMutH–GATC incisions. The mechanics of MMR strand specific excision that begins at a distant ssDNA break are not yet clear. Here the authors have used multiple single molecule imaging techniques to visualize the behavior of MMR components on mismatched DNA substrates and reveal an exonuclease-independent mechanism for E.coli MMR.
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Affiliation(s)
- Jiaquan Liu
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Ryanggeun Lee
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, Korea
| | - Brooke M Britton
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - James A London
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Keunsang Yang
- School of Interdisciplinary Bioscience and Bioengineering, POSTECH, Pohang, Gyeongbuk, 37673, Korea
| | - Jeungphill Hanne
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Jong-Bong Lee
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 37673, Korea. .,School of Interdisciplinary Bioscience and Bioengineering, POSTECH, Pohang, Gyeongbuk, 37673, Korea.
| | - Richard Fishel
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
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7
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El Meouche I, Dunlop MJ. Heterogeneity in efflux pump expression predisposes antibiotic-resistant cells to mutation. Science 2019; 362:686-690. [PMID: 30409883 DOI: 10.1126/science.aar7981] [Citation(s) in RCA: 128] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 06/07/2018] [Accepted: 09/19/2018] [Indexed: 12/12/2022]
Abstract
Antibiotic resistance is often the result of mutations that block drug activity; however, bacteria also evade antibiotics by transiently expressing genes such as multidrug efflux pumps. A crucial question is whether transient resistance can promote permanent genetic changes. Previous studies have established that antibiotic treatment can select tolerant cells that then mutate to achieve permanent resistance. Whether these mutations result from antibiotic stress or preexist within the population is unclear. To address this question, we focused on the multidrug pump AcrAB-TolC. Using time-lapse microscopy, we found that cells with higher acrAB expression have lower expression of the DNA mismatch repair gene mutS, lower growth rates, and higher mutation frequencies. Thus, transient antibiotic resistance from elevated acrAB expression can promote spontaneous mutations within single cells.
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Affiliation(s)
- Imane El Meouche
- Department of Biomedical Engineering and Biological Design Center, Boston University, Boston, MA 02215, USA.,School of Engineering, University of Vermont, Burlington, VT 05405, USA
| | - Mary J Dunlop
- Department of Biomedical Engineering and Biological Design Center, Boston University, Boston, MA 02215, USA. .,School of Engineering, University of Vermont, Burlington, VT 05405, USA
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8
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Abstract
The ability of bacteria to thrive in diverse habitats and to adapt to ever-changing environmental conditions relies on the rapid and stringent modulation of gene expression. It has become evident in the past decade that small regulatory RNAs (sRNAs) are central components of networks controlling the bacterial responses to stress. Functioning at the posttranscriptional level, sRNAs base-pair with cognate mRNAs to alter translation, stability, or both to either repress or activate the targeted transcripts; the RNA chaperone Hfq participates in stabilizing sRNAs and in promoting pairing between target and sRNA. In particular, sRNAs act at the heart of crucial stress responses, including those dedicated to overcoming membrane damage and oxidative stress, discussed here. The bacterial cell envelope is the outermost protective barrier against the environment and thus is constantly monitored and remodeled. Here, we review the integration of sRNAs into the complex networks of several major envelope stress responses of Gram-negative bacteria, including the RpoE (σE), Cpx, and Rcs regulons. Oxidative stress, caused by bacterial respiratory activity or induced by toxic molecules, can lead to significant damage of cellular components. In Escherichia coli and related bacteria, sRNAs also contribute significantly to the function of the RpoS (σS)-dependent general stress response as well as the specific OxyR- and SoxR/S-mediated responses to oxidative damage. Their activities in gene regulation and crosstalk to other stress-induced regulons are highlighted.
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9
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Liu J, Lee JB, Fishel R. Stochastic Processes and Component Plasticity Governing DNA Mismatch Repair. J Mol Biol 2018; 430:4456-4468. [PMID: 29864444 PMCID: PMC6461355 DOI: 10.1016/j.jmb.2018.05.039] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 05/09/2018] [Accepted: 05/28/2018] [Indexed: 02/06/2023]
Abstract
DNA mismatch repair (MMR) is a DNA excision-resynthesis process that principally enhances replication fidelity. Highly conserved MutS (MSH) and MutL (MLH/PMS) homologs initiate MMR and in higher eukaryotes act as DNA damage sensors that can trigger apoptosis. MSH proteins recognize mismatched nucleotides, whereas the MLH/PMS proteins mediate multiple interactions associated with downstream MMR events including strand discrimination and strand-specific excision that are initiated at a significant distance from the mismatch. Remarkably, the biophysical functions of the MLH/PMS proteins have been elusive for decades. Here we consider recent observations that have helped to define the mechanics of MLH/PMS proteins and their role in choreographing MMR. We highlight the stochastic nature of DNA interactions that have been visualized by single-molecule analysis and the plasticity of protein complexes that employ thermal diffusion to complete the progressions of MMR.
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Affiliation(s)
- Jiaquan Liu
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, 43210, OH, USA
| | - Jong-Bong Lee
- Department of Physics, Pohang University of Science and Technology (POSTECH), 790-784, Pohang, Korea; Interdisciplinary Bioscience and Bioengineering, POSTECH, 790-784, Pohang, Korea.
| | - Richard Fishel
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, 43210, OH, USA.
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10
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Woo AC, Faure L, Dapa T, Matic I. Heterogeneity of spontaneous DNA replication errors in single isogenic Escherichia coli cells. SCIENCE ADVANCES 2018; 4:eaat1608. [PMID: 29938224 PMCID: PMC6010332 DOI: 10.1126/sciadv.aat1608] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 05/14/2018] [Indexed: 06/06/2023]
Abstract
Despite extensive knowledge of the molecular mechanisms that control mutagenesis, it is not known how spontaneous mutations are produced in cells with fully operative mutation-prevention systems. By using a mutation assay that allows visualization of DNA replication errors and stress response transcriptional reporters, we examined populations of isogenic Escherichia coli cells growing under optimal conditions without exogenous stress. We found that spontaneous DNA replication errors in proliferating cells arose more frequently in subpopulations experiencing endogenous stresses, such as problems with proteostasis, genome maintenance, and reactive oxidative species production. The presence of these subpopulations of phenotypic mutators is not expected to affect the average mutation frequency or to reduce the mean population fitness in a stable environment. However, these subpopulations can contribute to overall population adaptability in fluctuating environments by serving as a reservoir of increased genetic variability.
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Affiliation(s)
- Anthony C. Woo
- INSERM U1001, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, 24 rue du Faubourg Saint-Jacques, 75014 Paris, France
| | - Louis Faure
- INSERM U1001, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, 24 rue du Faubourg Saint-Jacques, 75014 Paris, France
| | - Tanja Dapa
- INSERM U1001, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, 24 rue du Faubourg Saint-Jacques, 75014 Paris, France
| | - Ivan Matic
- INSERM U1001, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, 24 rue du Faubourg Saint-Jacques, 75014 Paris, France
- Centre National de la Recherche Scientifique, 75016 Paris, France
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11
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Suzuki H, Taketani T, Kobayashi J, Ohshiro T. Antibiotic resistance mutations induced in growing cells of Bacillus-related thermophiles. J Antibiot (Tokyo) 2018; 71:382-389. [PMID: 29348523 DOI: 10.1038/s41429-017-0003-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Revised: 10/12/2017] [Accepted: 10/23/2017] [Indexed: 12/20/2022]
Abstract
Stress-induced mutagenesis can assist pathogens in generating drug-resistant cells during antibiotic therapy; however, if and how antibiotics induce mutagenesis in microbes remains poorly understood. A non-pathogenic thermophile, Geobacillus kaustophilus HTA426, efficiently produces derivative cells resistant to rifampicin and streptomycin via rpoB and rpsL mutations, respectively. Here, we examined this phenomenon to suggest a novel mutagenic mode induced by antibiotics. Fluctuation analysis indicated that mutations occurred via spontaneous mutations during culture. However, mutations were much more frequent in growing cells than stationary cells, and mutation sites were varied through cell growth. These observations suggested that growing cells induced mutagenesis in response to antibiotics. An in-frame deletion of mfd, which governs transcription-coupled repair to correct DNA lesions on the transcribed strand, caused mutations that were comparable between growing and stationary cells; therefore, the mutagenic mechanism was attributable to DNA repair defects where growing cells depressed mfd function. Mutations occurred more frequently at optimal growth temperatures for G. kaustophilus than at a higher growth temperature, suggesting that the mutagenesis relies on active cellular activities rather than high temperature-associated DNA damage. In addition, the mutagenesis may involve a mutagenic factor targeting these sites, in addition to mfd depression, because rpoB and rpsL mutations were dominant at thymine and guanine sites on the transcribed strand. A similar mutagenic profile was observed for other Geobacillus and thermophilic Bacillus species. This suggests that Bacillus-related thermophiles commonly induce mutagenesis in response to rifampicin and streptomycin to produce resistant cells.
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Affiliation(s)
- Hirokazu Suzuki
- Functional Genomics of Extremophiles, Faculty of Agriculture, Graduate School, Kyushu University, 6-10-1 Hakozaki, Higashi-Ku, Fukuoka, 812-8581, Japan. .,Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori, 680-8550, Japan.
| | - Tatsunari Taketani
- Department of Engineering, Graduate School of Sustainability Science, Tottori University, 4-101 Koyama-Minami, Tottori, 680-8550, Japan
| | - Jyumpei Kobayashi
- Functional Genomics of Extremophiles, Faculty of Agriculture, Graduate School, Kyushu University, 6-10-1 Hakozaki, Higashi-Ku, Fukuoka, 812-8581, Japan.,Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori, 680-8550, Japan
| | - Takashi Ohshiro
- Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori, 680-8550, Japan
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12
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Elez M, Robert L, Matic I. Method for Detecting and Studying Genome-Wide Mutations in Single Living Cells in Real Time. Methods Mol Biol 2018; 1736:29-39. [PMID: 29322456 DOI: 10.1007/978-1-4939-7638-6_3] [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] [Indexed: 12/03/2022]
Abstract
DNA sequencing and fluctuation test have been choice methods for studying DNA mutations for decades. Although invaluable tools allowing many important discoveries on mutations, they are both highly influenced by fitness effects of mutations, and therefore suffer several limits. Fluctuation test is for example limited to mutations that produce an identifiable phenotype, which is the minority of all generated mutations. Genome-wide extrapolations using this method are therefore difficult. DNA sequencing detects almost all DNA mutations in population of cells. However, the obtained population mutation spectrum is biased because of the fitness effects of newly generated mutations. For example, mutations that affect fitness strongly and negatively are underrepresented, while those with a strong positive effect are overrepresented. Single-cell genome sequencing can solve this problem. However, sufficient amount of DNA for this approach is obtained by massive whole-genome amplification, which produces many artifacts.We describe the first direct method for monitoring genome-wide mutations in living cells independently of their effect on fitness. This method is based on the following three facts. First, DNA replication errors are the major source of DNA mutations. Second, these errors are the target for an evolutionarily conserved mismatch repair (MMR) system, which repairs the vast majority of replication errors. Third, we recently showed that the fluorescently labeled MMR protein MutL forms fluorescent foci on unrepaired replication errors. If not repaired, the new round of DNA synthesis fixes these errors in the genome permanently, i.e., they become mutations. Therefore, visualizing foci of the fluorescently tagged MutL in individual living cells allows detecting mutations as they appear, before the expression of the phenotype.
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Affiliation(s)
- Marina Elez
- iSSB, Genopole, CNRS, UEVE, Université Paris-Saclay, 91000, Évry, France., Evry, France. .,LJP, CNRS UMR 8237, UPMC, Sorbonne Universités, Paris, France, Paris, France.
| | - Lydia Robert
- LJP, CNRS UMR 8237, UPMC, Sorbonne Universités, Paris, France, Paris, France.,Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France, Jouy-en-Josas, France
| | - Ivan Matic
- INSERM U1001, Université Paris-Descartes, Sorbonne Paris Cité, Faculté de Médecine Paris Descartes, Paris, France. .,Centre National de la Recherche Scientifique (CNRS), Paris, France.
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13
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Chen J, Gottesman S. Hfq links translation repression to stress-induced mutagenesis in E. coli. Genes Dev 2017; 31:1382-1395. [PMID: 28794186 PMCID: PMC5580658 DOI: 10.1101/gad.302547.117] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 07/17/2017] [Indexed: 01/08/2023]
Abstract
Here, Chen et al. show an example of Hfq repressing translation in the absence of sRNAs via major remodeling of the mRNA. They demonstrate that, by interacting with the mutS leader, Hfq serves as a critical switch that modulates bacteria from high-fidelity DNA replication to stress-induced mutagenesis. Mismatch repair (MMR) is a conserved mechanism exploited by cells to correct DNA replication errors both in growing cells and under nongrowing conditions. Hfq (host factor for RNA bacteriophage Qβ replication), a bacterial Lsm family RNA-binding protein, chaperones RNA–RNA interactions between regulatory small RNAs (sRNAs) and target messenger RNAs (mRNAs), leading to alterations of mRNA translation and/or stability. Hfq has been reported to post-transcriptionally repress the DNA MMR gene mutS in stationary phase, possibly limiting MMR to allow increased mutagenesis. Here we report that Hfq deploys dual mechanisms to control mutS expression. First, Hfq binds directly to an (AAN)3 motif within the mutS 5′ untranslated region (UTR), repressing translation in the absence of sRNA partners both in vivo and in vitro. Second, Hfq acts in a canonical pathway, promoting base-pairing of ArcZ sRNA with the mutS leader to inhibit translation. Most importantly, using pathway-specific mutS chromosomal alleles that specifically abrogate either regulatory pathway or both, we demonstrate that tight control of MutS levels in stationary phase contributes to stress-induced mutagenesis. By interacting with the mutS leader, Hfq serves as a critical switch that modulates bacteria from high-fidelity DNA replication to stress-induced mutagenesis.
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Affiliation(s)
- Jiandong Chen
- Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892, USA
| | - Susan Gottesman
- Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892, USA
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14
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Mei GY, Tang J, Bach S, Kostrzynska M. Changes in Gene Transcription Induced by Hydrogen Peroxide Treatment of Verotoxin-Producing Escherichia coli O157:H7 and Non-O157 Serotypes on Romaine Lettuce. Front Microbiol 2017; 8:477. [PMID: 28377761 PMCID: PMC5359304 DOI: 10.3389/fmicb.2017.00477] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 03/08/2017] [Indexed: 01/05/2023] Open
Abstract
Disease outbreaks of verotoxin-producing Escherichia coli (VTEC) O157:H7 and non-O157 serotypes associated with leafy green vegetables are becoming a growing concern. A better understanding of the behavior of VTEC, particularly non-O157 serotypes, on lettuce under stress conditions is necessary for designing more effective control strategies. Hydrogen peroxide (H2O2) can be used as a sanitizer to reduce the microbial load in leafy green vegetables, particularly in fresh produce destined for the organic market. In this study, we tested the hypothesis that H2O2 treatment of contaminated lettuce affects in the same manner transcription of stress-associated and virulence genes in VTEC strains representing O157 and non-O157 serotypes. Six VTEC isolates representing serotypes O26:H11, O103:H2, O104:H4, O111:NM, O145:NM, and O157:H7 were included in this study. The results indicate that 50 mM H2O2 caused a population reduction of 2.4-2.8 log10 (compared to non-treated control samples) in all six VTEC strains present on romaine lettuce. Following the treatment, the transcription of genes related to oxidative stress (oxyR and sodA), general stress (uspA and rpoS), starvation (phoA), acid stress (gadA, gadB, and gadW), and virulence (stx1A, stx2A, and fliC) were dramatically downregulated in all six VTEC serotypes (P ≤ 0.05) compared to not treated control samples. Therefore, VTEC O157:H7 and non-O157 serotypes on lettuce showed similar survival rates and gene transcription profiles in response to 50 mM H2O2 treatment. Thus, the results derived from this study provide a basic understanding of the influence of H2O2 treatment on the survival and virulence of VTEC O157:H7 and non-O157 serotypes on lettuce.
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Affiliation(s)
- Gui-Ying Mei
- Guelph Research and Development Centre, Agriculture and Agri-Food Canada Guelph, ON, Canada
| | - Joshua Tang
- Guelph Research and Development Centre, Agriculture and Agri-Food Canada Guelph, ON, Canada
| | - Susan Bach
- Summerland Research and Development Centre, Agriculture and Agri-Food Canada Summerland, BC, Canada
| | - Magdalena Kostrzynska
- Guelph Research and Development Centre, Agriculture and Agri-Food Canada Guelph, ON, Canada
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15
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Liu J, Hanne J, Britton BM, Bennett J, Kim D, Lee JB, Fishel R. Cascading MutS and MutL sliding clamps control DNA diffusion to activate mismatch repair. Nature 2016; 539:583-587. [PMID: 27851738 PMCID: PMC5845140 DOI: 10.1038/nature20562] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 10/21/2016] [Indexed: 01/25/2023]
Abstract
Mismatched nucleotides arise from polymerase misincorporation errors, recombination between heteroallelic parents and chemical or physical DNA damage. Highly conserved MutS (MSH) and MutL (MLH/PMS) homologues initiate mismatch repair and, in higher eukaryotes, act as DNA damage sensors that can trigger apoptosis. Defects in human mismatch repair genes cause Lynch syndrome or hereditary non-polyposis colorectal cancer and 10-40% of related sporadic tumours. However, the collaborative mechanics of MSH and MLH/PMS proteins have not been resolved in any organism. We visualized Escherichia coli (Ec) ensemble mismatch repair and confirmed that EcMutS mismatch recognition results in the formation of stable ATP-bound sliding clamps that randomly diffuse along the DNA with intermittent backbone contact. The EcMutS sliding clamps act as a platform to recruit EcMutL onto the mismatched DNA, forming an EcMutS-EcMutL search complex that then closely follows the DNA backbone. ATP binding by EcMutL establishes a second long-lived DNA clamp that oscillates between the principal EcMutS-EcMutL search complex and unrestricted EcMutS and EcMutL sliding clamps. The EcMutH endonuclease that targets mismatch repair excision only binds clamped EcMutL, increasing its DNA association kinetics by more than 1,000-fold. The assembly of an EcMutS-EcMutL-EcMutH search complex illustrates how sequential stable sliding clamps can modulate one-dimensional diffusion mechanics along the DNA to direct mismatch repair.
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Affiliation(s)
- Jiaquan Liu
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210, USA
| | - Jeungphill Hanne
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210, USA
| | - Brooke M Britton
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210, USA
| | - Jared Bennett
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210, USA
| | - Daehyung Kim
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, Kyungbuk 790-784, Korea
| | - Jong-Bong Lee
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, Kyungbuk 790-784, Korea
- School of Interdisciplinary Bioscience and Bioengineering, POSTECH, Pohang, Kyungbuk, 790-784, Korea
| | - Richard Fishel
- Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210, USA
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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16
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Hermans N, Laffeber C, Cristovão M, Artola-Borán M, Mardenborough Y, Ikpa P, Jaddoe A, Winterwerp HHK, Wyman C, Jiricny J, Kanaar R, Friedhoff P, Lebbink JHG. Dual daughter strand incision is processive and increases the efficiency of DNA mismatch repair. Nucleic Acids Res 2016; 44:6770-86. [PMID: 27174933 PMCID: PMC5001592 DOI: 10.1093/nar/gkw411] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 05/03/2016] [Indexed: 12/27/2022] Open
Abstract
DNA mismatch repair (MMR) is an evolutionarily-conserved process responsible for the repair of replication errors. In Escherichia coli, MMR is initiated by MutS and MutL, which activate MutH to incise transiently-hemimethylated GATC sites. MMR efficiency depends on the distribution of these GATC sites. To understand which molecular events determine repair efficiency, we quantitatively studied the effect of strand incision on unwinding and excision activity. The distance between mismatch and GATC site did not influence the strand incision rate, and an increase in the number of sites enhanced incision only to a minor extent. Two GATC sites were incised by the same activated MMR complex in a processive manner, with MutS, the closed form of MutL and MutH displaying different roles. Unwinding and strand excision were more efficient on a substrate with two nicks flanking the mismatch, as compared to substrates containing a single nick or two nicks on the same side of the mismatch. Introduction of multiple nicks by the human MutLα endonuclease also contributed to increased repair efficiency. Our data support a general model of prokaryotic and eukaryotic MMR in which, despite mechanistic differences, mismatch-activated complexes facilitate efficient repair by creating multiple daughter strand nicks.
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Affiliation(s)
- Nicolaas Hermans
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands
| | - Charlie Laffeber
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands
| | - Michele Cristovão
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands
| | - Mariela Artola-Borán
- Institute of Molecular Cancer Research of the University of Zurich and ETH Zurich, Winterthurerstrasse 190, CH 8057 Zurich, Switzerland
| | - Yannicka Mardenborough
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands
| | - Pauline Ikpa
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands
| | - Aruna Jaddoe
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands
| | - Herrie H K Winterwerp
- Division of Biochemistry and Center for Biomedical Genetics, Netherlands Cancer Institute, 1006 BE Amsterdam, The Netherlands
| | - Claire Wyman
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands Department of Radiation Oncology, Erasmus Medical Center Rotterdam, 3015 CE Rotterdam, The Netherlands
| | - Josef Jiricny
- Institute of Molecular Cancer Research of the University of Zurich and ETH Zurich, Winterthurerstrasse 190, CH 8057 Zurich, Switzerland
| | - Roland Kanaar
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands Department of Radiation Oncology, Erasmus Medical Center Rotterdam, 3015 CE Rotterdam, The Netherlands
| | - Peter Friedhoff
- Institute for Biochemistry, Justus-Liebig-University, D-35392 Giessen, Germany
| | - Joyce H G Lebbink
- Department of Molecular Genetics, Cancer Genomics Netherlands, Erasmus Medical Center Rotterdam, 3015 AA Rotterdam,The Netherlands Department of Radiation Oncology, Erasmus Medical Center Rotterdam, 3015 CE Rotterdam, The Netherlands
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17
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Abstract
The DNA of Escherichia coli contains 19,120 6-methyladenines and 12,045 5-methylcytosines in addition to the four regular bases, and these are formed by the postreplicative action of three DNA methyltransferases. The majority of the methylated bases are formed by the Dam and Dcm methyltransferases encoded by the dam (DNA adenine methyltransferase) and dcm (DNA cytosine methyltransferase) genes. Although not essential, Dam methylation is important for strand discrimination during the repair of replication errors, controlling the frequency of initiation of chromosome replication at oriC, and the regulation of transcription initiation at promoters containing GATC sequences. In contrast, there is no known function for Dcm methylation, although Dcm recognition sites constitute sequence motifs for Very Short Patch repair of T/G base mismatches. In certain bacteria (e.g., Vibrio cholerae, Caulobacter crescentus) adenine methylation is essential, and, in C. crescentus, it is important for temporal gene expression, which, in turn, is required for coordinating chromosome initiation, replication, and division. In practical terms, Dam and Dcm methylation can inhibit restriction enzyme cleavage, decrease transformation frequency in certain bacteria, and decrease the stability of short direct repeats and are necessary for site-directed mutagenesis and to probe eukaryotic structure and function.
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Abstract
Early research on the origins and mechanisms of mutation led to the establishment of the dogma that, in the absence of external forces, spontaneous mutation rates are constant. However, recent results from a variety of experimental systems suggest that mutation rates can increase in response to selective pressures. This chapter summarizes data demonstrating that,under stressful conditions, Escherichia coli and Salmonella can increase the likelihood of beneficial mutations by modulating their potential for genetic change.Several experimental systems used to study stress-induced mutagenesis are discussed, with special emphasison the Foster-Cairns system for "adaptive mutation" in E. coli and Salmonella. Examples from other model systems are given to illustrate that stress-induced mutagenesis is a natural and general phenomenon that is not confined to enteric bacteria. Finally, some of the controversy in the field of stress-induced mutagenesis is summarized and discussed, and a perspective on the current state of the field is provided.
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19
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Abstract
The classical experiments of Luria and Delbrück showed convincingly that mutations exist before selection and do not contribute to the creation of mutations when selection is lethal. In contrast, when nonlethal selections are used,measuring mutation rates and separating the effects of mutation and selection are difficult and require methods to fully exclude growth after selection has been applied. Although many claims of stress-induced mutagenesis have been made, it is difficult to exclude the influence of growth under nonlethal selection conditions in accounting for the observed increases in mutant frequency. Instead, for many of the studied experimental systems the increase in mutant frequency can be explainedbetter by the ability of selection to detect small differences in growth rate caused by common small effect mutations. A verycommon mutant class,found in response to many different types of selective regimensin which increased gene dosage can resolve the problem, is gene amplification. In the well-studiedlac system of Cairns and Foster, the apparent increase in Lac+revertants can be explained by high-level amplification of the lac operon and the increased probability for a reversion mutation to occur in any one of the amplified copies. The associated increase in general mutation rate observed in revertant cells in that system is an artifact caused by the coincidental co-amplification of the nearby dinB gene (encoding the error-prone DNA polymerase IV) on the particular plasmid used for these experiments. Apart from the lac system, similar gene amplification processes have been described for adaptation to toxic drugs, growth in host cells, and various nutrient limitations.
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20
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Josephs EA, Zheng T, Marszalek PE. Atomic force microscopy captures the initiation of methyl-directed DNA mismatch repair. DNA Repair (Amst) 2015; 35:71-84. [PMID: 26466357 DOI: 10.1016/j.dnarep.2015.08.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Revised: 08/03/2015] [Accepted: 08/14/2015] [Indexed: 12/31/2022]
Abstract
In Escherichia coli, errors in newly-replicated DNA, such as the incorporation of a nucleotide with a mis-paired base or an accidental insertion or deletion of nucleotides, are corrected by a methyl-directed mismatch repair (MMR) pathway. While the enzymology of MMR has long been established, many fundamental aspects of its mechanisms remain elusive, such as the structures, compositions, and orientations of complexes of MutS, MutL, and MutH as they initiate repair. Using atomic force microscopy, we--for the first time--record the structures and locations of individual complexes of MutS, MutL and MutH bound to DNA molecules during the initial stages of mismatch repair. This technique reveals a number of striking and unexpected structures, such as the growth and disassembly of large multimeric complexes at mismatched sites, complexes of MutS and MutL anchoring latent MutH onto hemi-methylated d(GATC) sites or bound themselves at nicks in the DNA, and complexes directly bridging mismatched and hemi-methylated d(GATC) sites by looping the DNA. The observations from these single-molecule studies provide new opportunities to resolve some of the long-standing controversies in the field and underscore the dynamic heterogeneity and versatility of MutSLH complexes in the repair process.
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Affiliation(s)
- Eric A Josephs
- Department of Mechanical Engineering and Materials Science, Edmund T. Pratt, Jr. School of Engineering, Duke University, Durham NC 27708, USA.
| | - Tianli Zheng
- Department of Mechanical Engineering and Materials Science, Edmund T. Pratt, Jr. School of Engineering, Duke University, Durham NC 27708, USA; Department of Cell Biology, Duke University Medical Center, Durham NC 27708, USA
| | - Piotr E Marszalek
- Department of Mechanical Engineering and Materials Science, Edmund T. Pratt, Jr. School of Engineering, Duke University, Durham NC 27708, USA.
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21
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Monakhova M, Ryazanova A, Hentschel A, Viryasov M, Oretskaya T, Friedhoff P, Kubareva E. Chromatographic isolation of the functionally active MutS protein covalently linked to deoxyribonucleic acid. J Chromatogr A 2015; 1389:19-27. [PMID: 25746757 DOI: 10.1016/j.chroma.2015.02.045] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Revised: 02/10/2015] [Accepted: 02/16/2015] [Indexed: 12/11/2022]
Abstract
DNA metabolism is based on formation of different DNA-protein complexes which can adopt various conformations. To characterize functioning of such complexes, one needs a solution-based technique which allows fixing a complex in a certain transient conformation. The crosslinking approach is a popular tool for such studies. However, it is under debate if the protein components retain their natural activities in the resulting crosslinked complexes. In the present work we demonstrate the possibility of obtaining pure DNA conjugate with functionally active protein using as example MutS protein from Escherichia coli mismatch repair system. A conjugate of a chemically modified mismatch-containing DNA duplex with MutS is fixed by thiol-disulfide exchange reaction. To perform a reliable test of the protein activity in the conjugate, such conjugate must be thoroughly separated from the uncrosslinked protein and DNA prior to the test. In the present work, we employ anion exchange chromatography for this purpose for the first time and demonstrate this technique to be optimal for the conjugate purification. The activity test is a FRET-based detection of DNA unbending. We show experimentally that MutS in the conjugate retains its ability to unbend DNA in response to ATP addition and find out for the first time that the DNA unbending rate increases with increasing ATP concentration. Since the crosslinked complexes contain active MutS protein, they can be used in further experiments to investigate MutS interactions with other proteins of the mismatch repair system.
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Affiliation(s)
- Mayya Monakhova
- Chemistry Department and A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia
| | - Alexandra Ryazanova
- Chemistry Department and A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia
| | - Andreas Hentschel
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany
| | - Mikhail Viryasov
- Chemistry Department and A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia.
| | - Tatiana Oretskaya
- Chemistry Department and A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia
| | - Peter Friedhoff
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany
| | - Elena Kubareva
- Chemistry Department and A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia
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22
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Krašovec R, Belavkin RV, Aston JAD, Channon A, Aston E, Rash BM, Kadirvel M, Forbes S, Knight CG. Mutation rate plasticity in rifampicin resistance depends on Escherichia coli cell-cell interactions. Nat Commun 2014; 5:3742. [PMID: 24776982 PMCID: PMC4007418 DOI: 10.1038/ncomms4742] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 03/27/2014] [Indexed: 12/29/2022] Open
Abstract
Variation of mutation rate at a particular site in a particular genotype, in other words mutation rate plasticity (MRP), can be caused by stress or ageing. However, mutation rate control by other factors is less well characterized. Here we show that in wild-type Escherichia coli (K-12 and B strains), the mutation rate to rifampicin resistance is plastic and inversely related to population density: lowering density can increase mutation rates at least threefold. This MRP is genetically switchable, dependent on the quorum-sensing gene luxS--specifically its role in the activated methyl cycle--and is socially mediated via cell-cell interactions. Although we identify an inverse association of mutation rate with fitness under some circumstances, we find no functional link with stress-induced mutagenesis. Our experimental manipulation of mutation rates via the social environment raises the possibility that such manipulation occurs in nature and could be exploited medically.
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Affiliation(s)
- Rok Krašovec
- Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Manchester M13 9PT, UK
| | - Roman V. Belavkin
- School of Science and Technology, Middlesex University, London NW4 4BT, UK
| | - John A. D. Aston
- Statistical Laboratory, DPMMS, University of Cambridge, Cambridge CB3 0WB, UK
- Department of Statistics, University of Warwick, Warwick CV4 7AL, UK
| | - Alastair Channon
- Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele ST5 5BG, UK
| | - Elizabeth Aston
- Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele ST5 5BG, UK
| | - Bharat M. Rash
- Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Manchester M13 9PT, UK
| | - Manikandan Kadirvel
- Wolfson Molecular Imaging Centre, The University of Manchester, Manchester M20 3LJ, UK
- Manchester Pharmacy School, The University of Manchester, Manchester M13 9PT, UK
| | - Sarah Forbes
- Manchester Pharmacy School, The University of Manchester, Manchester M13 9PT, UK
| | - Christopher G. Knight
- Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Manchester M13 9PT, UK
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23
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Groothuizen FS, Fish A, Petoukhov MV, Reumer A, Manelyte L, Winterwerp HHK, Marinus MG, Lebbink JHG, Svergun DI, Friedhoff P, Sixma TK. Using stable MutS dimers and tetramers to quantitatively analyze DNA mismatch recognition and sliding clamp formation. Nucleic Acids Res 2013; 41:8166-81. [PMID: 23821665 PMCID: PMC3783165 DOI: 10.1093/nar/gkt582] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The process of DNA mismatch repair is initiated when MutS recognizes mismatched DNA bases and starts the repair cascade. The Escherichia coli MutS protein exists in an equilibrium between dimers and tetramers, which has compromised biophysical analysis. To uncouple these states, we have generated stable dimers and tetramers, respectively. These proteins allowed kinetic analysis of DNA recognition and structural analysis of the full-length protein by X-ray crystallography and small angle X-ray scattering. Our structural data reveal that the tetramerization domains are flexible with respect to the body of the protein, resulting in mostly extended structures. Tetrameric MutS has a slow dissociation from DNA, which can be due to occasional bending over and binding DNA in its two binding sites. In contrast, the dimer dissociation is faster, primarily dependent on a combination of the type of mismatch and the flanking sequence. In the presence of ATP, we could distinguish two kinetic groups: DNA sequences where MutS forms sliding clamps and those where sliding clamps are not formed efficiently. Interestingly, this inability to undergo a conformational change rather than mismatch affinity is correlated with mismatch repair.
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Affiliation(s)
- Flora S Groothuizen
- Division of Biochemistry and CancerGenomiCs.nl, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, the Netherlands, European Molecular Biology Laboratory, Hamburg Outstation, EMBL c/o DESY, Notkestrasse 85, 22607 Hamburg, Germany, Institute for Biochemistry, Justus Liebig University, Heinrich-Buff Ring 58, D-35392, Giessen, Germany, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA, Department of Cell Biology and Genetics, Cancer Genomics Center, Erasmus Medical Center, PO Box 2040, 3000 CA Rotterdam, the Netherlands and Department of Radiation Oncology, Erasmus Medical Center, PO Box 2040, 3000 CA Rotterdam, the Netherlands
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24
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Shimada A, Kawasoe Y, Hata Y, Takahashi TS, Masui R, Kuramitsu S, Fukui K. MutS stimulates the endonuclease activity of MutL in an ATP-hydrolysis-dependent manner. FEBS J 2013; 280:3467-79. [PMID: 23679952 DOI: 10.1111/febs.12344] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 05/02/2013] [Accepted: 05/07/2013] [Indexed: 11/30/2022]
Abstract
In the initial steps of DNA mismatch repair, MutS recognizes a mismatched base and recruits the latent endonuclease MutL onto the mismatch-containing DNA in concert with other proteins. MutL then cleaves the error-containing strand to introduce an entry point for the downstream excision reaction. Because MutL has no intrinsic ability to recognize a mismatch and discriminate between newly synthesized and template strands, the endonuclease activity of MutL is strictly regulated by ATP-binding in order to avoid nonspecific degradation of the genomic DNA. However, the activation mechanism for its endonuclease activity remains unclear. In this study, we found that the coexistence of a mismatch, ATP and MutS unlocks the ATP-binding-dependent suppression of MutL endonuclease activity. Interestingly, ATPase-deficient mutants of MutS were unable to activate MutL. Furthermore, wild-type MutS activated ATPase-deficient mutants of MutL less efficiently than wild-type MutL. We concluded that ATP hydrolysis by MutS and MutL is involved in the mismatch-dependent activation of MutL endonuclease activity.
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Affiliation(s)
- Atsuhiro Shimada
- Department of Biological Sciences, Graduate School of Science, Osaka University, Suita, Osaka, Japan
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25
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Belov OV, Chuluunbaatar O, Kapralov MI, Sweilam NH. The role of the bacterial mismatch repair system in SOS-induced mutagenesis: a theoretical background. J Theor Biol 2013; 332:30-41. [PMID: 23643530 DOI: 10.1016/j.jtbi.2013.04.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Revised: 04/20/2013] [Accepted: 04/22/2013] [Indexed: 10/26/2022]
Abstract
A theoretical study is performed of the possible role of the methyl-directed mismatch repair system in the ultraviolet-induced mutagenesis of Escherichia coli bacterial cells. For this purpose, mathematical models of the SOS network, translesion synthesis and mismatch repair are developed. Within the proposed models, the key pathways of these repair systems were simulated on the basis of modern experimental data related to their mechanisms. Our model approach shows a possible mechanistic explanation of the hypothesis that the bacterial mismatch repair system is responsible for attenuation of mutation frequency during ultraviolet-induced SOS response via removal of the nucleotides misincorporated by DNA polymerase V (the UmuD'2C complex).
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Affiliation(s)
- Oleg V Belov
- Laboratory of Radiation Biology, Joint Institute for Nuclear Research, 6 Joliot-Curie Street, 141980 Dubna, Moscow Region, Russia.
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26
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Magdanova LA, Golyasnaya NV. Heterogeneity as an adaptive trait of microbial populations. Microbiology (Reading) 2013. [DOI: 10.1134/s0026261713010074] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
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27
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Warnecke T, Supek F, Lehner B. Nucleoid-associated proteins affect mutation dynamics in E. coli in a growth phase-specific manner. PLoS Comput Biol 2012; 8:e1002846. [PMID: 23284284 PMCID: PMC3527292 DOI: 10.1371/journal.pcbi.1002846] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 11/03/2012] [Indexed: 02/06/2023] Open
Abstract
The binding of proteins can shield DNA from mutagenic processes but also interfere with efficient repair. How the presence of DNA-binding proteins shapes intra-genomic differences in mutability and, ultimately, sequence variation in natural populations, however, remains poorly understood. In this study, we examine sequence evolution in Escherichia coli in relation to the binding of four abundant nucleoid-associated proteins: Fis, H-NS, IhfA, and IhfB. We find that, for a subset of mutations, protein occupancy is associated with both increased and decreased mutability in the underlying sequence depending on when the protein is bound during the bacterial growth cycle. On average, protein-bound DNA exhibits reduced mutability compared to protein-free DNA. However, this net protective effect is weak and can be abolished or even reversed during stages of colony growth where binding coincides – and hence likely interferes with – DNA repair activity. We suggest that the four nucleoid-associated proteins analyzed here have played a minor but significant role in patterning extant sequence variation in E. coli. Mutations can be more or less likely to occur depending on whether DNA is naked or bound by proteins. On the one hand, DNA-binding proteins can shield the DNA from certain mutagenic processes. On the other hand, the very same proteins can interfere with efficient DNA repair. In this study, we reconstruct the history of mutations across 54 E. coli genomes and ask whether mutation risk is higher or lower in regions occupied by proteins that help organize bacterial DNA into chromatin. Intriguingly, we find that the effect of binding depends on its timing. When we consider genomic regions bound during stationary phase, we observe that binding is associated with lower mutation risk for some mutation classes compared to naked DNA, albeit weakly. However, when binding occurs during exponential phase, bound regions actually experience more mutations on average. We argue that this is because, during exponential phase, the major effect of binding is that it interferes with efficient DNA repair, whereas in stationary phase – when many repair pathways are inactive – the protective effect of binding dominates. Our results suggest that the four DNA-binding proteins considered here have a small but significant growth phase-specific effect on mutation dynamics in E. coli.
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Affiliation(s)
- Tobias Warnecke
- Bioinformatics and Genomics Program, Centre for Genomic Regulation (CRG), Barcelona, Spain.
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28
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Abstract
DNA mismatch repair (MMR) corrects replication errors in newly synthesized DNA. It also has an antirecombination action on heteroduplexes that contain similar but not identical sequences. This review focuses on the genetics and development of MMR and not on the latest biochemical mechanisms. The main focus is on MMR in Escherichia coli, but examples from Streptococcuspneumoniae and Bacillussubtilis have also been included. In most organisms, only MutS (detects mismatches) and MutL (an endonuclease) and a single exonucleaseare present. How this system discriminates between newlysynthesized and parental DNA strands is not clear. In E. coli and its relatives, however, Dam methylation is an integral part of MMR and is the basis for strand discrimination. A dedicated site-specific endonuclease, MutH, is present, andMutL has no endonuclease activity; four exonucleases can participate in MMR. Although it might seem that the accumulated wealth of genetic and biochemical data has given us a detailed picture of the mechanism of MMR in E. coli, the existence of three competing models to explain the initiation phase indicates the complexity of the system. The mechanism of the antirecombination action of MMR is largely unknown, but only MutS and MutL appear to be necessary. A primary site of action appears to be on RecA, although subsequent steps of the recombination process can also be inhibited. In this review, the genetics of Very Short Patch (VSP) repair of T/G mismatches arising from deamination of 5-methylcytosineresidues is also discussed.
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Lemarchand K, Lebaron P. Influence of mutation frequency on the persistence of Salmonella enterica serotypes in natural waters. FEMS Microbiol Ecol 2012; 41:125-31. [PMID: 19709246 DOI: 10.1111/j.1574-6941.2002.tb00973.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Abstract In aquatic environments, the survival of pathogenic microorganisms, such as Salmonella spp., may represent a risk to public health. The mutation frequency was hypothesized to influence the persistence of Salmonella serotypes in environmental waters. The mean mutation frequency to rifampin resistance of the 11 major serotypes of Salmonella enterica isolated from the Tech River (Pyrénées-Orientales, France) was determined. Then, a comparison of the survival of three serotypes holding different mutation frequencies showed no significant differences, suggesting that a high mutation rate was not directly linked to increased persistence of Salmonella cells under stressful conditions. However, we demonstrated, via controlled experiments, that long-term starvation in natural water could influence the mutation frequency of the Salmonella Typhimurium serotype. This effect, which was not observed for the serotypes Virchow and Infantis, could be a way of adapting to stressful conditions for the serotype Typhimurium and could explain its recurrence in aquatic systems.
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Affiliation(s)
- Karine Lemarchand
- Observatoire Océanologique de Banyuls, Laboratoire ARAGO, Université Pierre et Marie Curie (Paris 6), Institut National des Sciences de l'Univers (INSU), CNRS-UMR-7621, P.O. Box 44, 66651 Banyuls-sur-Mer Cedex, France
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Rate and molecular spectrum of spontaneous mutations in the bacterium Escherichia coli as determined by whole-genome sequencing. Proc Natl Acad Sci U S A 2012; 109:E2774-83. [PMID: 22991466 DOI: 10.1073/pnas.1210309109] [Citation(s) in RCA: 460] [Impact Index Per Article: 38.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Knowledge of the rate and nature of spontaneous mutation is fundamental to understanding evolutionary and molecular processes. In this report, we analyze spontaneous mutations accumulated over thousands of generations by wild-type Escherichia coli and a derivative defective in mismatch repair (MMR), the primary pathway for correcting replication errors. The major conclusions are (i) the mutation rate of a wild-type E. coli strain is ~1 × 10(-3) per genome per generation; (ii) mutations in the wild-type strain have the expected mutational bias for G:C > A:T mutations, but the bias changes to A:T > G:C mutations in the absence of MMR; (iii) during replication, A:T > G:C transitions preferentially occur with A templating the lagging strand and T templating the leading strand, whereas G:C > A:T transitions preferentially occur with C templating the lagging strand and G templating the leading strand; (iv) there is a strong bias for transition mutations to occur at 5'ApC3'/3'TpG5' sites (where bases 5'A and 3'T are mutated) and, to a lesser extent, at 5'GpC3'/3'CpG5' sites (where bases 5'G and 3'C are mutated); (v) although the rate of small (≤4 nt) insertions and deletions is high at repeat sequences, these events occur at only 1/10th the genomic rate of base-pair substitutions. MMR activity is genetically regulated, and bacteria isolated from nature often lack MMR capacity, suggesting that modulation of MMR can be adaptive. Thus, comparing results from the wild-type and MMR-defective strains may lead to a deeper understanding of factors that determine mutation rates and spectra, how these factors may differ among organisms, and how they may be shaped by environmental conditions.
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Ryall B, Eydallin G, Ferenci T. Culture history and population heterogeneity as determinants of bacterial adaptation: the adaptomics of a single environmental transition. Microbiol Mol Biol Rev 2012; 76:597-625. [PMID: 22933562 PMCID: PMC3429624 DOI: 10.1128/mmbr.05028-11] [Citation(s) in RCA: 102] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Diversity in adaptive responses is common within species and populations, especially when the heterogeneity of the frequently large populations found in environments is considered. By focusing on events in a single clonal population undergoing a single transition, we discuss how environmental cues and changes in growth rate initiate a multiplicity of adaptive pathways. Adaptation is a comprehensive process, and stochastic, regulatory, epigenetic, and mutational changes can contribute to fitness and overlap in timing and frequency. We identify culture history as a major determinant of both regulatory adaptations and microevolutionary change. Population history before a transition determines heterogeneities due to errors in translation, stochastic differences in regulation, the presence of aged, damaged, cheating, or dormant cells, and variations in intracellular metabolite or regulator concentrations. It matters whether bacteria come from dense, slow-growing, stressed, or structured states. Genotypic adaptations are history dependent due to variations in mutation supply, contingency gene changes, phase variation, lateral gene transfer, and genome amplifications. Phenotypic adaptations underpin genotypic changes in situations such as stress-induced mutagenesis or prophage induction or in biofilms to give a continuum of adaptive possibilities. Evolutionary selection additionally provides diverse adaptive outcomes in a single transition and generally does not result in single fitter types. The totality of heterogeneities in an adapting population increases the chance that at least some individuals meet immediate or future challenges. However, heterogeneity complicates the adaptomics of single transitions, and we propose that subpopulations will need to be integrated into future population biology and systems biology predictions of bacterial behavior.
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Affiliation(s)
- Ben Ryall
- School of Molecular Bioscience, University of Sydney, New South Wales, Australia
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32
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Woo JKK, Webb JS, Kirov SM, Kjelleberg S, Rice SA. Biofilm dispersal cells of a cystic fibrosis Pseudomonas aeruginosa isolate exhibit variability in functional traits likely to contribute to persistent infection. ACTA ACUST UNITED AC 2012; 66:251-64. [PMID: 22765766 DOI: 10.1111/j.1574-695x.2012.01006.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 05/11/2012] [Accepted: 06/27/2012] [Indexed: 12/30/2022]
Abstract
Persistent lung infection by Pseudomonas aeruginosa is typically associated with the development of biofilms, the appearance of morphotypic variants and reduction in the expression of acute virulence factors. We have characterised and compared functional traits [carbon substrate utilisation, attachment and biofilm formation, protease and elastase activity, quorum-sensing (QS)] of the biofilm dispersal populations of a representative P. aeruginosa isolate from a chronically infected cystic fibrosis individual and P. aeruginosa strain PAO1. The dispersal variants of the clinical strain exhibited significantly greater heterogeneity in all of the phenotypes tested. All morphotypic variants from the dispersal population of the clinical strain showed a significant increase in QS signal and elastase production compared to the parental strain. In contrast, isolates from planktonic cultures were phenotypically identical to the inoculum strain, suggesting that the appearance of these variants was biofilm specific. The clinical strain was shown to have a 3.4-fold higher mutation frequency than PAO1 which corroborated with the increased diversity of dispersal isolates. These data suggest that the development of a chronic infection phenotype can be reversed to recover acute infection isolates and that growth within a biofilm facilitates diversification of P. aeruginosa which is important for ecological adaptation.
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Affiliation(s)
- Jerry K K Woo
- School of Biotechnology and Biomolecular Sciences, Centre for Marine Bio-Innovation, University of New South Wales, Sydney, NSW, Australia
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Martin HA, Pedraza-Reyes M, Yasbin RE, Robleto EA. Transcriptional de-repression and Mfd are mutagenic in stressed Bacillus subtilis cells. J Mol Microbiol Biotechnol 2012; 21:45-58. [PMID: 22248542 DOI: 10.1159/000332751] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
In recent years, it has been proposed that conflicts between transcription and active chromosomal replication engender genome instability events. Furthermore, transcription elongation factors have been reported to prevent conflicts between transcription and replication and avoid genome instability. Here, we examined transcriptional de-repression as a genetic diversity-producing agent and showed, through the use of physiological and genetic means, that transcriptional de-represssion of a leuC defective allele leads to accumulation of Leu(+) mutations. We also showed, by using riboswitches that activate transcription in conditions of tyrosine or methionine starvation, that the effect of transcriptional de-repression of the leuC construct on the accumulation of Leu(+) mutations was independent of selection. We examined the role of Mfd, a transcription elongation factor involved in DNA repair, in this process and showed that proficiency of this factor promotes mutagenic events. These results are in stark contrast to previous reports in Escherichia coli, which showed that Mfd prevents replication fork collapses. Because our assays place cells under non-growing conditions, by starving them for two amino acids, we surmised that the Mfd mutagenic process associated with transcriptional de-repression does not result from conflicts with chromosomal replication. These results raise the interesting concept that transcription elongation factors may serve two functions in cells. In growing conditions, these factors prevent the generation of mutations, while in stress or non-growing conditions they mediate the production of genetic diversity.
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Elez M, Radman M, Matic I. Stoichiometry of MutS and MutL at unrepaired mismatches in vivo suggests a mechanism of repair. Nucleic Acids Res 2012; 40:3929-38. [PMID: 22241777 PMCID: PMC3351158 DOI: 10.1093/nar/gkr1298] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mismatch repair (MMR) is an evolutionarily conserved DNA repair system, which corrects mismatched bases arising during DNA replication. MutS recognizes and binds base pair mismatches, while the MutL protein interacts with MutS–mismatch complex and triggers MutH endonuclease activity at a distal-strand discrimination site on the DNA. The mechanism of communication between these two distal sites on the DNA is not known. We used functional fluorescent MMR proteins, MutS and MutL, in order to investigate the formation of the fluorescent MMR protein complexes on mismatches in real-time in growing Escherichia coli cells. We found that MutS and MutL proteins co-localize on unrepaired mismatches to form fluorescent foci. MutL foci were, on average, 2.7 times more intense than the MutS foci co-localized on individual mismatches. A steric block on the DNA provided by the MutHE56A mutant protein, which binds to but does not cut the DNA at the strand discrimination site, decreased MutL foci fluorescence 3-fold. This indicates that MutL accumulates from the mismatch site toward strand discrimination site along the DNA. Our results corroborate the hypothesis postulating that MutL accumulation assures the coordination of the MMR activities between the mismatch and the strand discrimination site.
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Affiliation(s)
- Marina Elez
- Université Paris-Descartes, Sorbonne Paris Cité, Inserm Unit 1001, 75015 Paris, France.
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Abstract
In their stressful natural environments, bacteria often are in stationary phase and use their limited resources for maintenance and stress survival. Underlying this activity is the general stress response, which in Escherichia coli depends on the σS (RpoS) subunit of RNA polymerase. σS is closely related to the vegetative sigma factor σ70 (RpoD), and these two sigmas recognize similar but not identical promoter sequences. During the postexponential phase and entry into stationary phase, σS is induced by a fine-tuned combination of transcriptional, translational, and proteolytic control. In addition, regulatory "short-cuts" to high cellular σS levels, which mainly rely on the rapid inhibition of σS proteolysis, are triggered by sudden starvation for various nutrients and other stressful shift conditons. σS directly or indirectly activates more than 500 genes. Additional signal input is integrated by σS cooperating with various transcription factors in complex cascades and feedforward loops. Target gene products have stress-protective functions, redirect metabolism, affect cell envelope and cell shape, are involved in biofilm formation or pathogenesis, or can increased stationary phase and stress-induced mutagenesis. This review summarizes these diverse functions and the amazingly complex regulation of σS. At the molecular level, these processes are integrated with the partitioning of global transcription space by sigma factor competition for RNA polymerase core enzyme and signaling by nucleotide second messengers that include cAMP, (p)ppGpp, and c-di-GMP. Physiologically, σS is the key player in choosing between a lifestyle associated with postexponential growth based on nutrient scavenging and motility and a lifestyle focused on maintenance, strong stress resistance, and increased adhesiveness. Finally, research with other proteobacteria is beginning to reveal how evolution has further adapted function and regulation of σS to specific environmental niches.
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Atomic force microscopy captures MutS tetramers initiating DNA mismatch repair. EMBO J 2011; 30:2881-93. [PMID: 21666597 DOI: 10.1038/emboj.2011.180] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Accepted: 05/10/2011] [Indexed: 11/09/2022] Open
Abstract
In spite of extensive research, the mechanism by which MutS initiates DNA mismatch repair (MMR) remains controversial. We use atomic force microscopy (AFM) to capture how MutS orchestrates the first step of E. coli MMR. AFM images captured two types of MutS/DNA complexes: single-site binding and loop binding. In most of the DNA loops imaged, two closely associated MutS dimers formed a tetrameric complex in which one of the MutS dimers was located at or near the mismatch. Surprisingly, in the presence of ATP, one MutS dimer remained at or near the mismatch site and the other, while maintaining contact with the first dimer, relocated on the DNA by reeling in DNA, thereby producing expanding DNA loops. Our results indicate that MutS tetramers composed of two non-equivalent MutS dimers drive E. coli MMR, and these new observations now reconcile the apparent contradictions of previous 'sliding' and 'bending/looping' models of interaction between mismatch and strand signal.
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Polosina YY, Cupples CG. Wot the 'L-Does MutL do? Mutat Res 2010; 705:228-38. [PMID: 20667509 DOI: 10.1016/j.mrrev.2010.07.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Revised: 07/13/2010] [Accepted: 07/14/2010] [Indexed: 11/26/2022]
Abstract
In model DNA, A pairs with T, and C with G. However, in vivo, the complementarity of the DNA strands may be disrupted by errors in DNA replication, biochemical modification of bases and recombination. In prokaryotic organisms, mispaired bases are recognized by MutS homologs which, together with MutL homologs, initiate mismatch repair. These same proteins also participate in base excision repair and nucleotide excision repair. In eukaryotes they regulate not just DNA repair but also meiotic recombination, cell-cycle delay and/or apoptosis in response to DNA damage, and hypermutation in immunoglobulin genes. Significantly, the same DNA mismatches that trigger repair in some circumstances trigger non-repair pathways in others. In this review, we argue that mismatch recognition by the MutS proteins is linked to these disparate biological outcomes through regulated interaction of MutL proteins with a wide variety of effector proteins.
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Affiliation(s)
- Yaroslava Y Polosina
- Department of Biochemistry and Microbiology, University of Victoria, PO Box 3055, STN CSC, Victoria, BC, Canada.
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38
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Trindade S, Perfeito L, Gordo I. Rate and effects of spontaneous mutations that affect fitness in mutator Escherichia coli. Philos Trans R Soc Lond B Biol Sci 2010; 365:1177-86. [PMID: 20308092 PMCID: PMC2871818 DOI: 10.1098/rstb.2009.0287] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Knowledge of the mutational parameters that affect the evolution of organisms is of key importance in understanding the evolution of several characteristics of many natural populations, including recombination and mutation rates. In this study, we estimated the rate and mean effect of spontaneous mutations that affect fitness in a mutator strain of Escherichia coli and review some of the estimation methods associated with mutation accumulation (MA) experiments. We performed an MA experiment where we followed the evolution of 50 independent mutator lines that were subjected to repeated bottlenecks of a single individual for approximately 1150 generations. From the decline in mean fitness and the increase in variance between lines, we estimated a minimum mutation rate to deleterious mutations of 0.005 (+/-0.001 with 95% confidence) and a maximum mean fitness effect per deleterious mutation of 0.03 (+/-0.01 with 95% confidence). We also show that any beneficial mutations that occur during the MA experiment have a small effect on the estimate of the rate and effect of deleterious mutations, unless their rate is extremely large. Extrapolating our results to the wild-type mutation rate, we find that our estimate of the mutational effects is slightly larger and the inferred deleterious mutation rate slightly lower than previous estimates obtained for non-mutator E. coli.
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Affiliation(s)
- Sandra Trindade
- Instituto Gulbenkian de Ciência, Rua da Quinta Grande, No. 6, 2780-156 Oeiras, Portugal
| | - Lilia Perfeito
- Instituto Gulbenkian de Ciência, Rua da Quinta Grande, No. 6, 2780-156 Oeiras, Portugal
- Institute for Genetics of the University of Cologne, Zuelpicher Street 47, Cologne 50674, Germany
- Institute for Theoretical Physics of the University of Cologne, Zuelpicher Street 77, Cologne 50937, Germany
| | - Isabel Gordo
- Instituto Gulbenkian de Ciência, Rua da Quinta Grande, No. 6, 2780-156 Oeiras, Portugal
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Interplay between pleiotropy and secondary selection determines rise and fall of mutators in stress response. PLoS Comput Biol 2010; 6:e1000710. [PMID: 20300650 PMCID: PMC2837395 DOI: 10.1371/journal.pcbi.1000710] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Accepted: 02/08/2010] [Indexed: 11/19/2022] Open
Abstract
Mutators are clones whose mutation rate is about two to three orders of magnitude higher than the rate of wild-type clones and their roles in adaptive evolution of asexual populations have been controversial. Here we address this problem by using an ab initio microscopic model of living cells, which combines population genetics with a physically realistic presentation of protein stability and protein-protein interactions. The genome of model organisms encodes replication controlling genes (RCGs) and genes modeling the mismatch repair (MMR) complexes. The genotype-phenotype relationship posits that the replication rate of an organism is proportional to protein copy numbers of RCGs in their functional form and there is a production cost penalty for protein overexpression. The mutation rate depends linearly on the concentration of homodimers of MMR proteins. By simulating multiple runs of evolution of populations under various environmental stresses—stationary phase, starvation or temperature-jump—we find that adaptation most often occurs through transient fixation of a mutator phenotype, regardless of the nature of stress. By contrast, the fixation mechanism does depend on the nature of stress. In temperature jump stress, mutators take over the population due to loss of stability of MMR complexes. In contrast, in starvation and stationary phase stresses, a small number of mutators are supplied to the population via epigenetic stochastic noise in production of MMR proteins (a pleiotropic effect), and their net supply is higher due to reduced genetic drift in slowly growing populations under stressful environments. Subsequently, mutators in stationary phase or starvation hitchhike to fixation with a beneficial mutation in the RCGs, (second order selection) and finally a mutation stabilizing the MMR complex arrives, returning the population to a non-mutator phenotype. Our results provide microscopic insights into the rise and fall of mutators in adapting finite asexual populations. The dramatic rise of mutators has been found to accompany adaptation of bacteria in response to many kinds of stress. Two views on the evolutionary origin of this phenomenon emerged: the pleiotropic hypothesis positing that it is a byproduct of environmental stress or other specific stress response mechanisms and the second order selection which states that mutators hitchhike to fixation with unrelated beneficial alleles. Conventional population genetics models could not fully resolve this controversy because they are based on certain assumptions about fitness landscape. Here we address this problem using a microscopic multiscale model, which couples physically realistic molecular descriptions of proteins and their interactions with population genetics of carrier organisms without assuming any a priori mutational effect on fitness landscape. We found that both pleiotropy and second order selection play a crucial role at different stages of adaptation: the supply of mutators is provided through destabilization of error correction complexes or, alternatively, fluctuations of production levels of prototypic mismatch repair proteins (pleiotropic effects), while the rise and fixation of mutators occurs when there is a sufficient supply of beneficial mutations in replication-controlling genes. This general mechanism assures a robust and reliable adaptation of organisms to unforeseen challenges. This study highlights physical principles underlying biological mechanisms of stress response and adaptation.
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Polosina YY, Cupples CG. MutL: conducting the cell's response to mismatched and misaligned DNA. Bioessays 2010; 32:51-9. [PMID: 19953589 DOI: 10.1002/bies.200900089] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Base pair mismatches in DNA arise from errors in DNA replication, recombination, and biochemical modification of bases. Mismatches are inherently transient. They are resolved passively by DNA replication, or actively by enzymatic removal and resynthesis of one of the bases. The first step in removal is recognition of strand discontinuity by one of the MutS proteins. Mismatches arising from errors in DNA replication are repaired in favor of the base on the template strand, but other mismatches trigger base excision or nucleotide excision repair (NER), or non-repair pathways such as hypermutation, cell cycle arrest, or apoptosis. We argue that MutL homologues play a key role in determining biologic outcome by recruiting and/or activating effector proteins in response to lesion recognition by MutS. We suggest that the process is regulated by conformational changes in MutL caused by cycles of ATP binding and hydrolysis, and by physiologic changes which influence effector availability.
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Affiliation(s)
- Yaroslava Y Polosina
- Department of Biochemistry and Microbiology, University of Victoria, BC, Canada.
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41
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Functional Analyses of Escherichia coli MutS-β Clamp Interaction In Vitro and In Vivo. Curr Microbiol 2009; 60:466-70. [DOI: 10.1007/s00284-009-9566-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2009] [Accepted: 12/07/2009] [Indexed: 10/20/2022]
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Abstract
The DNA of Escherichia coli contains 19,120 6-methyladenines and 12,045 5-methylcytosines in addition to the four regular bases, and these are formed by the postreplicative action of three DNA methyltransferases. The majority of the methylated bases are formed by the Dam and Dcmmethyltransferases encoded by the dam (DNA adenine methyltransferase) and dcm (DNA cytosine methyltransferase) genes. Although not essential, Dam methylation is important for strand discrimination during repair of replication errors, controlling the frequency of initiation of chromosome replication at oriC, and regulation of transcription initiation at promoters containing GATC sequences. In contrast, there is no known function for Dcm methylation, although Dcm recognition sites constitute sequence motifs for Very Short Patch repair of T/G base mismatches. In certain bacteria (e.g., Vibrio cholera and Caulobactercrescentus) adenine methylation is essential, and in C.crescentus it is important for temporal gene expression which, in turn, is required for coordination of chromosome initiation, replication, and division. In practical terms, Dam and Dcm methylation can inhibit restriction enzyme cleavage,decrease transformation frequency in certain bacteria,and decrease the stability of short direct repeats andare necessary for site-directed mutagenesis and to probe eukaryotic structure and function.
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Heinze RJ, Giron-Monzon L, Solovyova A, Elliot SL, Geisler S, Cupples CG, Connolly BA, Friedhoff P. Physical and functional interactions between Escherichia coli MutL and the Vsr repair endonuclease. Nucleic Acids Res 2009; 37:4453-63. [PMID: 19474347 PMCID: PMC2715241 DOI: 10.1093/nar/gkp380] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
DNA mismatch repair (MMR) and very-short patch (VSP) repair are two pathways involved in the repair of T:G mismatches. To learn about competition and cooperation between these two repair pathways, we analyzed the physical and functional interaction between MutL and Vsr using biophysical and biochemical methods. Analytical ultracentrifugation reveals a nucleotide-dependent interaction between Vsr and the N-terminal domain of MutL. Using chemical crosslinking, we mapped the interaction site of MutL for Vsr to a region between the N-terminal domains similar to that described before for the interaction between MutL and the strand discrimination endonuclease MutH of the MMR system. Competition between MutH and Vsr for binding to MutL resulted in inhibition of the mismatch-provoked MutS- and MutL-dependent activation of MutH, which explains the mutagenic effect of Vsr overexpression. Cooperation between MMR and VSP repair was demonstrated by the stimulation of the Vsr endonuclease in a MutS-, MutL- and ATP-hydrolysis-dependent manner, in agreement with the enhancement of VSP repair by MutS and MutL in vivo. These data suggest a mobile MutS–MutL complex in MMR signalling, that leaves the DNA mismatch prior to, or at the time of, activation of downstream effector molecules such as Vsr or MutH.
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Affiliation(s)
- Roger J Heinze
- Institut für Biochemie, Justus-Liebig-Universität, D-35392 Giessen, Germany
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Elevated mutation frequency in surviving populations of carbon-starved rpoS-deficient Pseudomonas putida is caused by reduced expression of superoxide dismutase and catalase. J Bacteriol 2009; 191:3604-14. [PMID: 19346306 DOI: 10.1128/jb.01803-08] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
RpoS is a bacterial sigma factor of RNA polymerase which is involved in the expression of a large number of genes to facilitate survival under starvation conditions and other stresses. The results of our study demonstrate that the frequency of emergence of base substitution mutants is significantly increased in long-term-starved populations of rpoS-deficient Pseudomonas putida cells. The increasing effect of the lack of RpoS on the mutation frequency became apparent in both a plasmid-based test system measuring Phe(+) reversion and a chromosomal rpoB system detecting rifampin-resistant mutants. The elevated mutation frequency coincided with the death of about 95% of the cells in a population of rpoS-deficient P. putida. Artificial overexpression of superoxide dismutase or catalase in the rpoS-deficient strain restored the survival of cells and resulted in a decline in the mutation frequency. This indicated that, compared to wild-type bacteria, rpoS-deficient cells are less protected against damage caused by reactive oxygen species. 7,8-Dihydro-8-oxoguanine (GO) is known to be one of the most stable and frequent base modifications caused by oxygen radical attack on DNA. However, the spectrum of base substitution mutations characterized in rpoS-deficient P. putida was different from that in bacteria lacking the GO repair system: it was broader and more similar to that identified in the wild-type strain. Interestingly, the formation of large deletions was also accompanied by a lack of RpoS. Thus, the accumulation of DNA damage other than GO elevates the frequency of mutation in these bacteria. It is known that oxidative damage of proteins and membrane components, but not that of DNA, is a major reason for the death of cells. Since the increased mutation frequency was associated with a decline in the viability of bacteria, we suppose that the elevation of the mutation frequency in the surviving population of carbon-starved rpoS-deficient P. putida may be caused both by oxidative damage of DNA and enzymes involved in DNA replication and repair fidelity.
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45
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Influences of capsule on cell shape and chain formation of wild-type and pcsB mutants of serotype 2 Streptococcus pneumoniae. J Bacteriol 2009; 191:3024-40. [PMID: 19270090 DOI: 10.1128/jb.01505-08] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
PcsB is a protein of unknown function that plays a critical role in cell division in Streptococcus pneumoniae and other ovococcus species of Streptococcus. We constructed isogenic sets of mutants expressing different amounts of PcsB in laboratory strain R6 and virulent serotype 2 strain D39 to evaluate its cellular roles. Insertion mutagenesis in parent and pcsB(+) merodiploid strains indicated that pcsB is essential in serotype 2 S. pneumoniae. Quantitative Western blotting of wild-type and epitope-tagged PcsB showed that all PcsB was processed into cell-associated and secreted forms of the same molecular mass and that cell-associated PcsB was moderately abundant and present at approximately 4,900 monomers per cell. Controlled expression and complementation experiments indicated that there was a causative relationship between the severity of defects in cell division and decreasing PcsB amount. These experiments also showed that perturbations of expression of the upstream mreCD genes did not contribute to the cell division defects of pcsB mutants and that mreCD could be deleted. Unexpectedly, capsule influenced the cell shape and chain formation phenotypes of the wild-type D39 strain and mutants underexpressing PcsB or deleted for other genes involved in peptidoglycan biosynthesis, such as dacA. Underexpression of PcsB did not result in changes in the amounts or composition of lactoyl-peptides, which were markedly different in the R6 and D39 strains, and there was no correlation between decreased PcsB amount and sensitivity to penicillin. Finally, microarray analyses indicated that underexpression of PcsB may generate a signal that increases expression of the VicRK regulon, which includes pcsB.
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Guggenheim ER, Xu D, Zhang CX, Chang PV, Lippard SJ. Photoaffinity isolation and identification of proteins in cancer cell extracts that bind to platinum-modified DNA. Chembiochem 2009; 10:141-57. [PMID: 19053130 PMCID: PMC2710532 DOI: 10.1002/cbic.200800471] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2008] [Indexed: 12/13/2022]
Abstract
The activity of the anticancer drug cisplatin is a consequence of its ability to bind DNA. Platinum adducts bend and unwind the DNA duplex, creating recognition sites for nuclear proteins. Following DNA damage recognition, the lesions will either be repaired, facilitating cell viability, or if repair is unsuccessful and the Pt adduct interrupts vital cellular functions, apoptosis will follow. With the use of the benzophenone-modified cisplatin analogue Pt-BP6, 25 bp DNA duplexes containing either a 1,2-d(G*pG*) intrastrand or a 1,3-d(G*pTpG*) intrastrand crosslink were synthesized, where the asterisks designate platinated nucleobases. Proteins having affinity for these platinated DNAs were photocrosslinked and identified in cervical, testicular, pancreatic and bone cancer-cell nuclear extracts. Proteins identified in this manner include the DNA repair factors RPA1, Ku70, Ku80, Msh2, DNA ligase III, PARP-1, and DNA-PKcs, as well as HMG-domain proteins HMGB1, HMGB2, HMGB3, and UBF1. The latter strongly associate with the 1,2-d(G*pG*) adduct and weakly or not at all with the 1,3-d(G*pTpG*) adduct. The nucleotide excision repair protein RPA1 was photocrosslinked only by the probe containing a 1,3-d(G*pTpG*) intrastrand crosslink. The affinity of PARP-1 for platinum-modified DNA was established using this type of probe for the first time. To ensure that the proteins were not photocrosslinked because of an affinity for DNA ends, a 90-base dumbbell probe modified with Pt-BP6 was investigated. Photocrosslinking experiments with this longer probe revealed the same proteins, as well as some additional proteins involved in chromatin remodeling, transcription, or repair. These findings reveal a more complete list of proteins involved in the early steps of the mechanism of action of the cisplatin and its close analogue carboplatin than previously was available.
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Affiliation(s)
- Evan R. Guggenheim
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Telephone: 617-253-1892 , Fax: 617-258-8150
| | - Dong Xu
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Telephone: 617-253-1892 , Fax: 617-258-8150
| | - Christiana X. Zhang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Telephone: 617-253-1892 , Fax: 617-258-8150
| | - Pamela V. Chang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Telephone: 617-253-1892 , Fax: 617-258-8150
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Telephone: 617-253-1892 , Fax: 617-258-8150
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Savic DJ. Adaptive mutations: a challenge to neo-Darwinism? Sci Prog 2009; 92:447-68. [PMID: 19960882 PMCID: PMC10368342 DOI: 10.3184/003685009x12547510332277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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48
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Abstract
Bacteria spend their lives buffeted by changing environmental conditions. To adapt to and survive these stresses, bacteria have global response systems that result in sweeping changes in gene expression and cellular metabolism. These responses are controlled by master regulators, which include: alternative sigma factors, such as RpoS and RpoH; small molecule effectors, such as ppGpp; gene repressors such as LexA; and, inorganic molecules, such as polyphosphate. The response pathways extensively overlap and are induced to various extents by the same environmental stresses. These stresses include nutritional deprivation, DNA damage, temperature shift, and exposure to antibiotics. All of these global stress responses include functions that can increase genetic variability. In particular, up-regulation and activation of error-prone DNA polymerases, down-regulation of error-correcting enzymes, and movement of mobile genetic elements are common features of several stress responses. The result is that under a variety of stressful conditions, bacteria are induced for genetic change. This transient mutator state may be important for adaptive evolution.
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Affiliation(s)
- Patricia L Foster
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
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Ferenci T. Bacterial physiology, regulation and mutational adaptation in a chemostat environment. Adv Microb Physiol 2007; 53:169-229. [PMID: 17707145 DOI: 10.1016/s0065-2911(07)53003-1] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The chemostat was devised over 50 years ago and rapidly adopted for studies of bacterial physiology and mutation. Despite the long history and earlier analyses, the complexity of events in continuous cultures is only now beginning to be resolved. The application of techniques for following regulatory and mutational changes and the identification of mutated genes in chemostat populations has provided new insights into bacterial behaviour. Inoculation of bacteria into a chemostat culture results in a population competing for a limiting amount of a particular resource. Any utilizable carbon source or ion can be a limiting nutrient and bacteria respond to limitation through a regulated nutrient-specific hunger response. In addition to transcriptional responses to nutrient limitation, a second regulatory influence in a chemostat culture is the reduced growth rate fixed by the dilution rate in individual experiments. Sub-maximal growth rates and hunger result in regulation involving sigma factors and alarmones like cAMP and ppGpp. Reduced growth rate also results in increased mutation frequencies. The combination of a strongly selective environment (where mutants able to compete for limiting nutrient have a major fitness advantage) and elevated mutation rates (both endogenous and through the secondary enrichment of mutators) results in a population that changes rapidly and persistently over many generations. Contrary to common belief, the chemostat environment is never in "steady state" with fixed bacterial characteristics usable for clean comparisons of physiological or regulatory states. Adding to the complexity, chemostat populations do not simply exhibit a succession of mutational sweeps leading to a dominant winner clone. Instead, within 100 generations large populations become heterogeneous and evolving bacteria adopt alternative, parallel fitness strategies. Transport physiology, metabolism and respiration, as well as growth yields, are highly diverse in chemostat-evolved bacteria. The rich assortment of changes in an evolving chemostat provides an excellent experimental system for understanding bacterial evolution. The adaptive radiation or divergence of populations into a collection of individuals with alternative solutions to the challenge of chemostat existence provides an ideal model system for testing evolutionary and ecological theories on adaptive radiations and the generation of bacterial diversity.
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Affiliation(s)
- Thomas Ferenci
- School of Molecular and Microbial Biosciences G08, The University of Sydney, NSW 2006, Australia
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Abstract
It has recently become clear that the classical notion of the random nature of mutation does not hold for the distribution of mutations among genes: most collections of mutants contain more isolates with two or more mutations than predicted by the mutant frequency on the assumption of a random distribution of mutations. Excesses of multiples are seen in a wide range of organisms, including riboviruses, DNA viruses, prokaryotes, yeasts, and higher eukaryotic cell lines and tissues. In addition, such excesses are produced by DNA polymerases in vitro. These "multiples" appear to be generated by transient, localized hypermutation rather than by heritable mutator mutations. The components of multiples are sometimes scattered at random and sometimes display an excess of smaller distances between mutations. As yet, almost nothing is known about the mechanisms that generate multiples, but such mutations have the capacity to accelerate those evolutionary pathways that require multiple mutations where the individual mutations are neutral or deleterious. Examples that impinge on human health may include carcinogenesis and the adaptation of microbial pathogens as they move between individual hosts.
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Affiliation(s)
- John W Drake
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709-2233, USA.
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