1
|
Pedraza-Reyes M, Abundiz-Yañez K, Rangel-Mendoza A, Martínez LE, Barajas-Ornelas RC, Cuéllar-Cruz M, Leyva-Sánchez HC, Ayala-García VM, Valenzuela-García LI, Robleto EA. Bacillus subtilis stress-associated mutagenesis and developmental DNA repair. Microbiol Mol Biol Rev 2024; 88:e0015823. [PMID: 38551349 PMCID: PMC11332352 DOI: 10.1128/mmbr.00158-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024] Open
Abstract
SUMMARYThe metabolic conditions that prevail during bacterial growth have evolved with the faithful operation of repair systems that recognize and eliminate DNA lesions caused by intracellular and exogenous agents. This idea is supported by the low rate of spontaneous mutations (10-9) that occur in replicating cells, maintaining genome integrity. In contrast, when growth and/or replication cease, bacteria frequently process DNA lesions in an error-prone manner. DNA repairs provide cells with the tools needed for maintaining homeostasis during stressful conditions and depend on the developmental context in which repair events occur. Thus, different physiological scenarios can be anticipated. In nutritionally stressed bacteria, different components of the base excision repair pathway may process damaged DNA in an error-prone approach, promoting genetic variability. Interestingly, suppressing the mismatch repair machinery and activating specific DNA glycosylases promote stationary-phase mutations. Current evidence also suggests that in resting cells, coupling repair processes to actively transcribed genes may promote multiple genetic transactions that are advantageous for stressed cells. DNA repair during sporulation is of interest as a model to understand how transcriptional processes influence the formation of mutations in conditions where replication is halted. Current reports indicate that transcriptional coupling repair-dependent and -independent processes operate in differentiating cells to process spontaneous and induced DNA damage and that error-prone synthesis of DNA is involved in these events. These and other noncanonical ways of DNA repair that contribute to mutagenesis, survival, and evolution are reviewed in this manuscript.
Collapse
Affiliation(s)
- Mario Pedraza-Reyes
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | - Karen Abundiz-Yañez
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | - Alejandra Rangel-Mendoza
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | - Lissett E. Martínez
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | - Rocío C. Barajas-Ornelas
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | - Mayra Cuéllar-Cruz
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | | | | | - Luz I. Valenzuela-García
- Department of Sustainable Engineering, Advanced Materials Research Center (CIMAV), Arroyo Seco, Durango, Mexico
| | | |
Collapse
|
2
|
Idola D, Mori H, Nagata Y, Nonaka L, Yano H. Host range of strand-biased circularizing integrative elements: a new class of mobile DNA elements nesting in Gammaproteobacteria. Mob DNA 2023; 14:7. [PMID: 37237359 DOI: 10.1186/s13100-023-00295-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 05/19/2023] [Indexed: 05/28/2023] Open
Abstract
BACKGROUND The strand-biased circularizing integrative elements (SEs) are putatively non-mobilizable integrative elements for transmitting antimicrobial resistance genes. The transposition mode and the prevalence of SEs in prokaryotes remain vague. RESULTS To corroborate the transposition mode and the prevalence of SEs, hypothetical transposition intermediates of an SE were searched for in genomic DNA fractions of an SE host. Then, the SE core genes were defined based on gene knockout experiments, and the synteny blocks of their distant homologs were searched for in the RefSeq complete genome sequence database using PSI-BLAST. A genomic DNA fractionation experiment revealed that SE copies are present in a double-stranded nicked circular form in vivo. Operonic structure of three conserved coding sequences (intA, tfp, intB) and srap located at the left end of SEs were identified as essential for attL × attR recombination. The synteny blocks of tfp and srap homologs were detected in 3.6% of the replicons of Gammaproteobacteria but not in other taxa, implying that SE movement is host-dependent. SEs have been discovered most frequently in the orders Vibrionales (19% of replicons), Pseudomonadales (18%), Alteromonadales (17%), and Aeromonadales (12%). Genomic comparisons revealed 35 new SE members with identifiable termini. SEs are present at 1 to 2 copies per replicon and have a median length of 15.7 kb. Three newly identified SE members carry antimicrobial resistance genes, like tmexCD-toprJ, mcr-9, and blaGMA-1. Further experiments validated that three new SE members possess the strand-biased attL × attR recombination activity. CONCLUSIONS This study suggested that transposition intermediates of SEs are double-stranded circular DNA. The main hosts of SEs are a subset of free-living Gammaproteobacteria; this represents a rather narrow host range compared to those of mobile DNA element groups discovered to date. As the host range, genetic organization, and movements are unique among the mobile DNA elements, SEs provide a new model system for host-mobile DNA element coevolution studies.
Collapse
Affiliation(s)
- Desmila Idola
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aobaku, Sendai, 980-8577, Japan
| | - Hiroshi Mori
- Department of Informatics, National Institute of Genetics, 1111 Yata, Mishima, 411-8540, Japan
| | - Yuji Nagata
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aobaku, Sendai, 980-8577, Japan
| | - Lisa Nonaka
- Faculty of Human Life Sciences, Shokei University, 2-6-78 Kuhonji, Kumamoto, 862-8678, Japan
| | - Hirokazu Yano
- Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aobaku, Sendai, 980-8577, Japan.
- Antimicrobial Resistance Research Center, National Institute of Infectious Diseases, 4-2-1 Aobacho, Higashimurayama, Tokyo, 189-0002, Japan.
| |
Collapse
|
3
|
Barona-Gómez F, Chevrette MG, Hoskisson PA. On the evolution of natural product biosynthesis. Adv Microb Physiol 2023; 83:309-349. [PMID: 37507161 DOI: 10.1016/bs.ampbs.2023.05.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/30/2023]
Abstract
Natural products are the raw material for drug discovery programmes. Bioactive natural products are used extensively in medicine and agriculture and have found utility as antibiotics, immunosuppressives, anti-cancer drugs and anthelminthics. Remarkably, the natural role and what mechanisms drive evolution of these molecules is relatively poorly understood. The exponential increase in genome and chemical data in recent years, coupled with technical advances in bioinformatics and genetics have enabled progress to be made in understanding the evolution of biosynthetic gene clusters and the products of their enzymatic machinery. Here we discuss the diversity of natural products, incorporating the mechanisms that govern evolution of metabolic pathways and how this can be applied to biosynthetic gene clusters. We build on the nomenclature of natural products in terms of primary, integrated, secondary and specialised metabolism and place this within an ecology-evolutionary-developmental biology framework. This eco-evo-devo framework we believe will help to clarify the nature and use of the term specialised metabolites in the future.
Collapse
Affiliation(s)
| | - Marc G Chevrette
- Department of Microbiology and Cell Sciences, University of Florida, Museum Drive, Gainesville, FL, United States; University of Florida Genetics Institute, University of Florida, Mowry Road, Gainesville, FL, United States
| | - Paul A Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Cathedral Street, Glasgow, United Kingdom.
| |
Collapse
|
4
|
Tellechea-Luzardo J, Hobbs L, Velázquez E, Pelechova L, Woods S, de Lorenzo V, Krasnogor N. Versioning biological cells for trustworthy cell engineering. Nat Commun 2022; 13:765. [PMID: 35140226 PMCID: PMC8828774 DOI: 10.1038/s41467-022-28350-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 01/21/2022] [Indexed: 11/18/2022] Open
Abstract
“Full-stack” biotechnology platforms for cell line (re)programming are on the horizon, thanks mostly to (a) advances in gene synthesis and editing techniques as well as (b) the growing integration of life science research with informatics, the internet of things and automation. These emerging platforms will accelerate the production and consumption of biological products. Hence, traceability, transparency, and—ultimately—trustworthiness is required from cradle to grave for engineered cell lines and their engineering processes. Here we report a cloud-based version control system for biotechnology that (a) keeps track and organizes the digital data produced during cell engineering and (b) molecularly links that data to the associated living samples. Barcoding protocols, based on standard genetic engineering methods, to molecularly link to the cloud-based version control system six species, including gram-negative and gram-positive bacteria as well as eukaryote cells, are shown. We argue that version control for cell engineering marks a significant step toward more open, reproducible, easier to trace and share, and more trustworthy engineering biology. Full traceability and transparency are important to establish trust in engineered cell lines. Here the authors argue that version control for cell engineering marks a significant step toward more open, reproducible, traceable and ultimately more trustworthy engineering biology.
Collapse
Affiliation(s)
- Jonathan Tellechea-Luzardo
- Interdisciplinary Computing and Complex Biosystems (ICOS) Research Group, Newcastle University, Newcastle Upon Tyne, NE4 5TG, UK
| | - Leanne Hobbs
- Interdisciplinary Computing and Complex Biosystems (ICOS) Research Group, Newcastle University, Newcastle Upon Tyne, NE4 5TG, UK
| | - Elena Velázquez
- Systems and Synthetic Biology Department, Centro Nacional de Biotecnología (CNB-CSIC), 28049, Madrid, Spain
| | - Lenka Pelechova
- Interdisciplinary Computing and Complex Biosystems (ICOS) Research Group, Newcastle University, Newcastle Upon Tyne, NE4 5TG, UK
| | - Simon Woods
- Policy Ethics and Life Sciences (PEALS), Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK
| | - Víctor de Lorenzo
- Systems and Synthetic Biology Department, Centro Nacional de Biotecnología (CNB-CSIC), 28049, Madrid, Spain
| | - Natalio Krasnogor
- Interdisciplinary Computing and Complex Biosystems (ICOS) Research Group, Newcastle University, Newcastle Upon Tyne, NE4 5TG, UK.
| |
Collapse
|
5
|
A Novel Gene Cluster Is Involved in the Degradation of Lignin-Derived Monoaromatics in Thermus oshimai JL-2. Appl Environ Microbiol 2021; 87:AEM.01589-20. [PMID: 33741620 DOI: 10.1128/aem.01589-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 03/09/2021] [Indexed: 11/20/2022] Open
Abstract
A novel gene cluster involved in the degradation of lignin-derived monoaromatics such as p-hydroxybenzoate, vanillate, and ferulate has been identified in the thermophilic nitrate reducer Thermus oshimai JL-2. Based on conserved domain analyses and metabolic pathway mapping, the cluster was classified into upper- and peripheral-pathway operons. The upper-pathway genes, responsible for the degradation of p-hydroxybenzoate and vanillate, are located on a 0.27-Mb plasmid, whereas the peripheral-pathway genes, responsible for the transformation of ferulate, are spread throughout the plasmid and the chromosome. In addition, a lower-pathway operon was also identified in the plasmid that corresponds to the meta-cleavage pathway of catechol. Spectrophotometric and gene induction data suggest that the upper and lower operons are induced by p-hydroxybenzoate, which the strain can degrade completely within 4 days of incubation, whereas the peripheral genes are expressed constitutively. The upper degradation pathway follows a less common route, proceeding via the decarboxylation of protocatechuate to form catechol, and involves a novel thermostable γ-carboxymuconolactone decarboxylase homolog, identified as protocatechuate decarboxylase based on gene deletion experiments. This gene cluster is conserved in only a few members of the Thermales and shows traces of vertical expansion of catabolic pathways in these organisms toward lignoaromatics.IMPORTANCE High-temperature steam treatment of lignocellulosic biomass during the extraction of cellulose and hemicellulose fractions leads to the release of a wide array of lignin-derived aromatics into the natural ecosystem, some of which can have detrimental effects on the environment. Not only will identifying organisms capable of using such aromatics aid in environmental cleanup, but thermostable enzymes, if characterized, can also be used for efficient lignin valorization. However, no thermophilic lignin degraders have been reported thus far. The present study reports T. oshimai JL-2 as a thermophilic bacterium with the potential to use lignin-derived aromatics. The identification of a novel thermostable protocatechuate decarboxylase gene in the strain further adds to its significance, as such an enzyme can be efficiently used in the biosynthesis of cis,cis-muconate, an important intermediate in the commercial production of plastics.
Collapse
|
6
|
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]
|
7
|
Abstract
Pseudomonas putidais a fast-growing bacterium found mostly in temperate soil and water habitats. The metabolic versatility ofP. putidamakes this organism attractive for biotechnological applications such as biodegradation of environmental pollutants and synthesis of added-value chemicals (biocatalysis). This organism has been extensively studied in respect to various stress responses, mechanisms of genetic plasticity and transcriptional regulation of catabolic genes.P. putidais able to colonize the surface of living organisms, but is generally considered to be of low virulence. A number ofP. putidastrains are able to promote plant growth. The aim of this review is to give historical overview of the discovery of the speciesP. putidaand isolation and characterization ofP. putidastrains displaying potential for biotechnological applications. This review also discusses some major findings inP. putidaresearch encompassing regulation of catabolic operons, stress-tolerance mechanisms and mechanisms affecting evolvability of bacteria under conditions of environmental stress.
Collapse
|
8
|
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.
Collapse
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
| |
Collapse
|
9
|
Implementation of a loss-of-function system to determine growth and stress-associated mutagenesis in Bacillus subtilis. PLoS One 2017; 12:e0179625. [PMID: 28700593 PMCID: PMC5507404 DOI: 10.1371/journal.pone.0179625] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Accepted: 06/01/2017] [Indexed: 11/19/2022] Open
Abstract
A forward mutagenesis system based on the acquisition of mutations that inactivate the thymidylate synthase gene (TMS) and confer a trimethoprim resistant (Tmpr) phenotype was developed and utilized to study transcription-mediated mutagenesis (TMM). In addition to thyA, Bacillus subtilis possesses thyB, whose expression occurs under conditions of cell stress; therefore, we generated a thyB- thyA+ mutant strain. Tmpr colonies of this strain were produced with a spontaneous mutation frequency of ~1.4 × 10-9. Genetic disruption of the canonical mismatch (MMR) and guanine oxidized (GO) repair pathways increased the Tmpr frequency of mutation by ~2-3 orders of magnitude. A wide spectrum of base substitutions as well as insertion and deletions in the ORF of thyA were found to confer a Tmpr phenotype. Stationary-phase-associated mutagenesis (SPM) assays revealed that colonies with a Tmpr phenotype, accumulated over a period of ten days with a frequency of ~ 60 ×10-7. The Tmpr system was further modified to study TMM by constructing a ΔthyA ΔthyB strain carrying an IPTG-inducible Pspac-thyA cassette. In conditions of transcriptional induction of thyA, the generation of Tmpr colonies increased ~3-fold compared to conditions of transcriptional repression. Further, the Mfd and GreA factors were necessary for the generation of Tmpr colonies in the presence of IPTG in B. subtilis. Because GreA and Mfd facilitate transcription-coupled repair, our results suggest that TMM is a mechanim to produce genetic diversity in highly transcribed regions in growth-limited B. subtilis cells.
Collapse
|
10
|
Tagel M, Tavita K, Hõrak R, Kivisaar M, Ilves H. A novel papillation assay for the identification of genes affecting mutation rate in Pseudomonas putida and other pseudomonads. Mutat Res 2016; 790:41-55. [PMID: 27447898 DOI: 10.1016/j.mrfmmm.2016.06.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Revised: 06/20/2016] [Accepted: 06/22/2016] [Indexed: 06/06/2023]
Abstract
Formation of microcolonies (papillae) permits easy visual screening of mutational events occurring in single colonies of bacteria. In this study, we have established a novel papillation assay employable in a wide range of pseudomonads including Pseudomonas aeruginosa and Pseudomonas putida for monitoring mutation frequency in distinct colonies. With the aid of this assay, we conducted a genome-wide search for the factors affecting mutation frequency in P. putida. Screening ∼27,000 transposon mutants for increased mutation frequency allowed us to identify 34 repeatedly targeted genes. In addition to genes involved in DNA replication and repair, we identified genes participating in metabolism and transport of secondary metabolites, cell motility, and cell wall synthesis. The highest effect on mutant frequency was observed when truA (tRNA pseudouridine synthase), mpl (UDP-N-acetylmuramate-alanine ligase) or gacS (multi-sensor hybrid histidine kinase) were inactivated. Inactivation of truA elevated the mutant frequency only in growing cells, while the deficiency of gacS affected mainly stationary-phase mutagenesis. Thus, our results demonstrate the feasibility of the assay for isolating mutants with elevated mutagenesis in growing as well as stationary-phase bacteria.
Collapse
Affiliation(s)
- Mari Tagel
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Kairi Tavita
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Rita Hõrak
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Maia Kivisaar
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Heili Ilves
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
| |
Collapse
|
11
|
George KW, Hay AG. Bacterial strategies for growth on aromatic compounds. ADVANCES IN APPLIED MICROBIOLOGY 2016; 74:1-33. [PMID: 21459192 DOI: 10.1016/b978-0-12-387022-3.00005-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Although the biodegradation of aromatic compounds has been studied for over 40 years, there is still much to learn about the strategies bacteria employ for growth on novel substrates. Elucidation of these strategies is crucial for predicting the environmental fate of aromatic pollutants and will provide a framework for the development of engineered bacteria and degradation pathways. In this chapter, we provide an overview of studies that have advanced our knowledge of bacterial adaptation to aromatic compounds. We have divided these strategies into three broad categories: (1) recruitment of catabolic genes, (2) expression of "repair" or detoxification proteins, and (3) direct alteration of enzymatic properties. Specific examples from the literature are discussed, with an eye toward the molecular mechanisms that underlie each strategy.
Collapse
Affiliation(s)
- Kevin W George
- Field of Environmental Toxicology, Cornell University Ithaca, New York, USA; Department of Microbiology, Wing Hall, Cornell University Ithaca, New York, USA
| | | |
Collapse
|
12
|
Vandecraen J, Monsieurs P, Mergeay M, Leys N, Aertsen A, Van Houdt R. Zinc-Induced Transposition of Insertion Sequence Elements Contributes to Increased Adaptability of Cupriavidus metallidurans. Front Microbiol 2016; 7:359. [PMID: 27047473 PMCID: PMC4803752 DOI: 10.3389/fmicb.2016.00359] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 03/07/2016] [Indexed: 12/15/2022] Open
Abstract
Bacteria can respond to adverse environments by increasing their genomic variability and subsequently facilitating adaptive evolution. To demonstrate this, the contribution of Insertion Sequence (IS) elements to the genetic adaptation of Cupriavidus metallidurans AE126 to toxic zinc concentrations was determined. This derivative of type strain CH34, devoid of its main zinc resistance determinant, is still able to increase its zinc resistance level. Specifically, upon plating on medium supplemented with a toxic zinc concentration, resistant variants arose in which a compromised cnrYX regulatory locus caused derepression of CnrH sigma factor activity and concomitant induction of the corresponding RND-driven cnrCBA efflux system. Late-occurring zinc resistant variants likely arose in response to the selective conditions, as they were enriched in cnrYX disruptions caused by specific IS elements whose transposase expression was found to be zinc-responsive. Interestingly, deletion of cnrH, and consequently the CnrH-dependent adaptation potential, still enabled adaptation by transposition of IS elements (ISRme5 and IS1086) that provided outward-directed promoters driving cnrCBAT transcription. Finally, adaptation to zinc by IS reshuffling can also enhance the adaptation to subsequent environmental challenges. Thus, transposition of IS elements can be induced by stress conditions and play a multifaceted, pivotal role in the adaptation to these and subsequent stress conditions.
Collapse
Affiliation(s)
- Joachim Vandecraen
- Unit of Microbiology, Belgian Nuclear Research Centre (SCK•CEN)Mol, Belgium; Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre, Department of Microbial and Molecular Systems, Faculty of Bioscience Engineering, Katholieke Universiteit LeuvenLeuven, Belgium
| | - Pieter Monsieurs
- Unit of Microbiology, Belgian Nuclear Research Centre (SCK•CEN) Mol, Belgium
| | - Max Mergeay
- Unit of Microbiology, Belgian Nuclear Research Centre (SCK•CEN) Mol, Belgium
| | - Natalie Leys
- Unit of Microbiology, Belgian Nuclear Research Centre (SCK•CEN) Mol, Belgium
| | - Abram Aertsen
- Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre, Department of Microbial and Molecular Systems, Faculty of Bioscience Engineering, Katholieke Universiteit Leuven Leuven, Belgium
| | - Rob Van Houdt
- Unit of Microbiology, Belgian Nuclear Research Centre (SCK•CEN) Mol, Belgium
| |
Collapse
|
13
|
Weakly Deleterious Mutations and Low Rates of Recombination Limit the Impact of Natural Selection on Bacterial Genomes. mBio 2015; 6:e01302-15. [PMID: 26670382 PMCID: PMC4701828 DOI: 10.1128/mbio.01302-15] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Free-living bacteria are usually thought to have large effective population sizes, and so tiny selective differences can drive their evolution. However, because recombination is infrequent, “background selection” against slightly deleterious alleles should reduce the effective population size (Ne) by orders of magnitude. For example, for a well-mixed population with 1012 individuals and a typical level of homologous recombination (r/m = 3, i.e., nucleotide changes due to recombination [r] occur at 3 times the mutation rate [m]), we predict that Ne is <107. An argument for high Ne values for bacteria has been the high genetic diversity within many bacterial “species,” but this diversity may be due to population structure: diversity across subpopulations can be far higher than diversity within a subpopulation, which makes it difficult to estimate Ne correctly. Given an estimate of Ne, standard population genetics models imply that selection should be sufficient to drive evolution if Ne × s is >1, where s is the selection coefficient. We found that this remains approximately correct if background selection is occurring or when population structure is present. Overall, we predict that even for free-living bacteria with enormous populations, natural selection is only a significant force if s is above 10−7 or so. Because bacteria form huge populations with trillions of individuals, the simplest theoretical prediction is that the better allele at a site would predominate even if its advantage was just 10−9 per generation. In other words, virtually every nucleotide would be at the local optimum in most individuals. A more sophisticated theory considers that bacterial genomes have millions of sites each and selection events on these many sites could interfere with each other, so that only larger effects would be important. However, bacteria can exchange genetic material, and in principle, this exchange could eliminate the interference between the evolution of the sites. We used simulations to confirm that during multisite evolution with realistic levels of recombination, only larger effects are important. We propose that advantages of less than 10−7 are effectively neutral.
Collapse
|
14
|
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.
Collapse
|
15
|
Paris Ü, Mikkel K, Tavita K, Saumaa S, Teras R, Kivisaar M. NHEJ enzymes LigD and Ku participate in stationary-phase mutagenesis in Pseudomonas putida. DNA Repair (Amst) 2015; 31:11-8. [PMID: 25942369 DOI: 10.1016/j.dnarep.2015.04.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 03/30/2015] [Accepted: 04/21/2015] [Indexed: 11/17/2022]
Abstract
Under growth-restricting conditions bacterial populations can rapidly evolve by a process known as stationary-phase mutagenesis. Bacterial nonhomologous end-joining (NHEJ) system which consists of the DNA-end-binding enzyme Ku and the multifunctional DNA ligase LigD has been shown to be important for survival of bacteria especially during quiescent states, such as late stationary-phase populations or sporulation. In this study we provide genetic evidence that NHEJ enzymes participate in stationary-phase mutagenesis in a population of carbon-starved Pseudomonas putida. Both the absence of LigD or Ku resulted in characteristic spectra of stationary-phase mutations that differed from each other and also from the wild-type spectrum. This indicates that LigD and Ku may participate also in mutagenic pathways that are independent from each other. Our results also imply that both phosphoesterase (PE) and polymerase (POL) domains of the LigD protein are involved in the occurrence of mutations in starving P. putida. The participation of both Ku and LigD in the occurrence of stationary-phase mutations was further supported by the results of the analysis of mutation spectra in stationary-phase sigma factor RpoS-minus background. The spectra of mutations identified in the RpoS-minus background were also distinct if LigD or Ku was absent. Interestingly, the effects of the presence of these enzymes on the frequency of occurrence of certain types of mutations were different or even opposite in the RpoS-proficient and deficient backgrounds. These results imply that RpoS affects performance of mutagenic pathways in starving P. putida that utilize LigD and/or Ku.
Collapse
Affiliation(s)
- Ülvi Paris
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, 23 Riia Street, 51010 Tartu, Estonia
| | - Katren Mikkel
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, 23 Riia Street, 51010 Tartu, Estonia
| | - Kairi Tavita
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, 23 Riia Street, 51010 Tartu, Estonia
| | - Signe Saumaa
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, 23 Riia Street, 51010 Tartu, Estonia
| | - Riho Teras
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, 23 Riia Street, 51010 Tartu, Estonia
| | - Maia Kivisaar
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, 23 Riia Street, 51010 Tartu, Estonia.
| |
Collapse
|
16
|
Barajas-Ornelas RDC, Ramírez-Guadiana FH, Juárez-Godínez R, Ayala-García VM, Robleto EA, Yasbin RE, Pedraza-Reyes M. Error-prone processing of apurinic/apyrimidinic (AP) sites by PolX underlies a novel mechanism that promotes adaptive mutagenesis in Bacillus subtilis. J Bacteriol 2014; 196:3012-22. [PMID: 24914186 PMCID: PMC4135629 DOI: 10.1128/jb.01681-14] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Accepted: 06/05/2014] [Indexed: 01/19/2023] Open
Abstract
In growing cells, apurinic/apyrimidinic (AP) sites generated spontaneously or resulting from the enzymatic elimination of oxidized bases must be processed by AP endonucleases before they compromise cell integrity. Here, we investigated how AP sites and the processing of these noncoding lesions by the AP endonucleases Nfo, ExoA, and Nth contribute to the production of mutations (hisC952, metB5, and leuC427) in starved cells of the Bacillus subtilis YB955 strain. Interestingly, cells from this strain that were deficient for Nfo, ExoA, and Nth accumulated a greater amount of AP sites in the stationary phase than during exponential growth. Moreover, under growth-limiting conditions, the triple nfo exoA nth knockout strain significantly increased the amounts of adaptive his, met, and leu revertants produced by the B. subtilis YB955 parental strain. Of note, the number of stationary-phase-associated reversions in the his, met, and leu alleles produced by the nfo exoA nth strain was significantly decreased following disruption of polX. In contrast, during growth, the reversion rates in the three alleles tested were significantly increased in cells of the nfo exoA nth knockout strain deficient for polymerase X (PolX). Therefore, we postulate that adaptive mutations in B. subtilis can be generated through a novel mechanism mediated by error-prone processing of AP sites accumulated in the stationary phase by the PolX DNA polymerase.
Collapse
Affiliation(s)
| | | | - Rafael Juárez-Godínez
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | - Victor M Ayala-García
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| | - Eduardo A Robleto
- School of Life Sciences, University of Nevada, Las Vegas, Nevada, USA
| | - Ronald E Yasbin
- College of Arts and Sciences, University of Missouri-St. Louis, St. Louis, Missouri, USA
| | - Mario Pedraza-Reyes
- Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico
| |
Collapse
|
17
|
Martínez-García E, Jatsenko T, Kivisaar M, de Lorenzo V. FreeingPseudomonas putida KT2440 of its proviral load strengthens endurance to environmental stresses. Environ Microbiol 2014; 17:76-90. [DOI: 10.1111/1462-2920.12492] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Accepted: 04/18/2014] [Indexed: 11/30/2022]
Affiliation(s)
- Esteban Martínez-García
- Systems Biology Program; Centro Nacional de Biotecnología-CSIC; Campus de Cantoblanco 28049 Madrid Spain
| | - Tatjana Jatsenko
- Department of Genetics; Institute of Molecular and Cell Biology; University of Tartu; Tartu Estonia
| | - Maia Kivisaar
- Department of Genetics; Institute of Molecular and Cell Biology; University of Tartu; Tartu Estonia
| | - Víctor de Lorenzo
- Systems Biology Program; Centro Nacional de Biotecnología-CSIC; Campus de Cantoblanco 28049 Madrid Spain
| |
Collapse
|
18
|
Pérez-Pantoja D, Kim J, Silva-Rocha R, de Lorenzo V. The differential response of thePbenpromoter ofPseudomonas putida mt-2 to BenR and XylS prevents metabolic conflicts inm-xylene biodegradation. Environ Microbiol 2014; 17:64-75. [DOI: 10.1111/1462-2920.12443] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Revised: 02/13/2014] [Accepted: 02/21/2014] [Indexed: 11/30/2022]
Affiliation(s)
- Danilo Pérez-Pantoja
- Systems and Synthetic Biology Program; Centro Nacional de Biotecnologia; Madrid Spain
| | - Juhyun Kim
- Systems and Synthetic Biology Program; Centro Nacional de Biotecnologia; Madrid Spain
| | - Rafael Silva-Rocha
- Systems and Synthetic Biology Program; Centro Nacional de Biotecnologia; Madrid Spain
| | - Víctor de Lorenzo
- Systems and Synthetic Biology Program; Centro Nacional de Biotecnologia; Madrid Spain
| |
Collapse
|
19
|
Abstract
Determining the molecular changes that give rise to functional innovations is a major unresolved problem in biology. The paucity of examples has served as a significant hindrance in furthering our understanding of this process. Here we used experimental evolution with the bacterium Escherichia coli to quantify the molecular changes underlying functional innovation in 68 independent instances ranging over 22 different metabolic functions. Using whole-genome sequencing, we show that the relative contribution of regulatory and structural mutations depends on the cellular context of the metabolic function. In addition, we find that regulatory mutations affect genes that act in pathways relevant to the novel function, whereas structural mutations affect genes that act in unrelated pathways. Finally, we use population genetic modeling to show that the relative contributions of regulatory and structural mutations during functional innovation may be affected by population size. These results provide a predictive framework for the molecular basis of evolutionary innovation, which is essential for anticipating future evolutionary trajectories in the face of rapid environmental change.
Collapse
|
20
|
Monti MR, Morero NR, Miguel V, Argaraña CE. nfxB as a novel target for analysis of mutation spectra in Pseudomonas aeruginosa. PLoS One 2013; 8:e66236. [PMID: 23762483 PMCID: PMC3676378 DOI: 10.1371/journal.pone.0066236] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 05/02/2013] [Indexed: 02/06/2023] Open
Abstract
nfxB encodes a negative regulator of the mexCD-oprJ genes for drug efflux in the opportunistic pathogen Pseudomonas aeruginosa. Inactivating mutations in this transcriptional regulator constitute one of the main mechanisms of resistance to ciprofloxacin (Cipr). In this work, we evaluated the use of nfxB/Cipr as a new test system to study mutation spectra in P. aeruginosa. The analysis of 240 mutations in nfxB occurring spontaneously in the wild-type and mutator backgrounds or induced by mutagens showed that nfxB/Cipr offers several advantages compared with other mutation detection systems. Identification of nfxB mutations was easy since the entire open reading frame and its promoter region were sequenced from the chromosome using a single primer. Mutations detected in nfxB included all transitions and transversions, 1-bp deletions and insertions, >1-bp deletions and duplications. The broad mutation spectrum observed in nfxB relies on the selection of loss-of-function changes, as we confirmed by generating a structural model of the NfxB repressor and evaluating the significance of each detected mutation. The mutation spectra characterized in the mutS, mutT, mutY and mutM mutator backgrounds or induced by the mutagenic agents 2-aminopurine, cisplatin and hydrogen peroxide were in agreement with their predicted mutational specificities. Additionally, this system allowed the analysis of sequence context effects since point mutations occurred at 85 different sites distributed over the entire nfxB. Significant hotspots and preferred sequence contexts were observed for spontaneous and mutagen-induced mutation spectra. Finally, we demonstrated the utility of a luminescence-based reporter for identification of nfxB mutants previous to sequencing analysis. Thus, the nfxB/Cipr system in combination with the luminescent reporter may be a valuable tool for studying mutational processes in Pseudomonas spp. wherein the genes encoding the NfxB repressor and the associated efflux pump are conserved.
Collapse
Affiliation(s)
- Mariela R. Monti
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, Argentina
| | - Natalia R. Morero
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, Argentina
| | - Virginia Miguel
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, Argentina
| | - Carlos E. Argaraña
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, Argentina
- * E-mail:
| |
Collapse
|
21
|
Juurik T, Ilves H, Teras R, Ilmjärv T, Tavita K, Ukkivi K, Teppo A, Mikkel K, Kivisaar M. Mutation frequency and spectrum of mutations vary at different chromosomal positions of Pseudomonas putida. PLoS One 2012; 7:e48511. [PMID: 23119042 PMCID: PMC3485313 DOI: 10.1371/journal.pone.0048511] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Accepted: 09/25/2012] [Indexed: 11/18/2022] Open
Abstract
It is still an open question whether mutation rate can vary across the bacterial chromosome. In this study, the occurrence of mutations within the same mutational target sequences at different chromosomal locations of Pseudomonas putida was monitored. For that purpose we constructed two mutation detection systems, one for monitoring the occurrence of a broad spectrum of mutations and transposition of IS element IS1411 inactivating LacI repressor, and another for detecting 1-bp deletions. Our results revealed that both the mutation frequency and the spectrum of mutations vary at different chromosomal positions. We observed higher mutation frequencies when the direction of transcription of the mutational target gene was opposite to the direction of replisome movement in the chromosome and vice versa, lower mutation frequency was accompanied with co-directional transcription and replication. Additionally, asymmetry of frameshift mutagenesis at homopolymeric and repetitive sequences during the leading and lagging-strand replication was found. The transposition frequency of IS1411 was also affected by the chromosomal location of the target site, which implies that regional differences in chromosomal topology may influence transposition of this mobile element. The occurrence of mutations in the P. putida chromosome was investigated both in growing and in stationary-phase bacteria. We found that the appearance of certain mutational hot spots is strongly affected by the chromosomal location of the mutational target sequence especially in growing bacteria. Also, artificial increasing transcription of the mutational target gene elevated the frequency of mutations in growing bacteria.
Collapse
Affiliation(s)
- Triinu Juurik
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Heili Ilves
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Riho Teras
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Tanel Ilmjärv
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Kairi Tavita
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Kärt Ukkivi
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Annika Teppo
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Katren Mikkel
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | - Maia Kivisaar
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
- * E-mail:
| |
Collapse
|
22
|
Tavita K, Mikkel K, Tark-Dame M, Jerabek H, Teras R, Sidorenko J, Tegova R, Tover A, Dame RT, Kivisaar M. Homologous recombination is facilitated in starving populations of Pseudomonas putida by phenol stress and affected by chromosomal location of the recombination target. Mutat Res 2012; 737:12-24. [PMID: 22917545 DOI: 10.1016/j.mrfmmm.2012.07.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Revised: 07/18/2012] [Accepted: 07/25/2012] [Indexed: 06/01/2023]
Abstract
Homologous recombination (HR) has a major impact in bacterial evolution. Most of the knowledge about the mechanisms and control of HR in bacteria has been obtained in fast growing bacteria. However, in their natural environment bacteria frequently meet adverse conditions which restrict the growth of cells. We have constructed a test system to investigate HR between a plasmid and a chromosome in carbon-starved populations of the soil bacterium Pseudomonas putida restoring the expression of phenol monooxygenase gene pheA. Our results show that prolonged starvation of P. putida in the presence of phenol stimulates HR. The emergence of recombinants on selective plates containing phenol as an only carbon source for the growth of recombinants is facilitated by reactive oxygen species and suppressed by DNA mismatch repair enzymes. Importantly, the chromosomal location of the HR target influences the frequency and dynamics of HR events. In silico analysis of binding sites of nucleoid-associated proteins (NAPs) revealed that chromosomal DNA regions which flank the test system in bacteria exhibiting a lower HR frequency are enriched in binding sites for a subset of NAPs compared to those which express a higher frequency of HR. We hypothesize that the binding of these proteins imposes differences in local structural organization of the genome that could affect the accessibility of the chromosomal DNA to HR processes and thereby the frequency of HR.
Collapse
Affiliation(s)
- Kairi Tavita
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, Tartu, Estonia
| | | | | | | | | | | | | | | | | | | |
Collapse
|
23
|
Abstract
Transcriptional activation or ‘rewiring’ of silent genes is an important, yet poorly understood, phenomenon in prokaryotic genomes. Anecdotal evidence coming from experimental evolution studies in bacterial systems has shown the promptness of adaptation upon appropriate selective pressure. In many cases, a partial or complete promoter is mobilized to silent genes from elsewhere in the genome. We term hereafter such recruited regulatory sequences as Putative Mobile Promoters (PMPs) and we hypothesize they have a large impact on rapid adaptation of novel or cryptic functions. Querying all publicly available prokaryotic genomes (1362) uncovered >4000 families of highly conserved PMPs (50 to 100 long with ≥80% nt identity) in 1043 genomes from 424 different genera. The genomes with the largest number of PMP families are Anabaena variabilis (28 families), Geobacter uraniireducens (27 families) and Cyanothece PCC7424 (25 families). Family size varied from 2 to 93 homologous promoters (in Desulfurivibrio alkaliphilus). Some PMPs are present in particular species, but some are conserved across distant genera. The identified PMPs represent a conservative dataset of very recent or conserved events of mobilization of non-coding DNA and thus they constitute evidence of an extensive reservoir of recyclable regulatory sequences for rapid transcriptional rewiring.
Collapse
Affiliation(s)
- Mariana Matus-Garcia
- Department of Agrotechnology and Food Sciences, Laboratory of Systems and Synthetic Biology, Wageningen University, 6703HB Wageningen, The Netherlands
| | | | | |
Collapse
|
24
|
Yano H, Genka H, Ohtsubo Y, Nagata Y, Top EM, Tsuda M. Cointegrate-resolution of toluene-catabolic transposon Tn4651: determination of crossover site and the segment required for full resolution activity. Plasmid 2012; 69:24-35. [PMID: 22878084 DOI: 10.1016/j.plasmid.2012.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 07/19/2012] [Accepted: 07/23/2012] [Indexed: 12/27/2022]
Abstract
Tn3-family transposon Tn4651 from Pseudomonas putida mt-2 plasmid pWW0 carries two divergently transcribed genes, tnpS and tnpT, for cointegrate-resolution. While tnpS encodes a tyrosine recombinase, tnpT encodes a protein that shows no homology to any other characterized protein. The Tn4651 resolution site was previously mapped within the 203-bp fragment that covered the tnpS and tnpT promoter region. To better understand the molecular mechanisms underlying the Tn4651 cointegrate-resolution, we determined the extent of the functional resolution site (designated the rst site) of Tn4651 and the location of the crossover site for the cointegrate-resolution. Deletion analysis of the rst region localized the fully functional rst site to a 136-bp segment. The analysis of the site-specific recombination between Tn4651 rst and a rst variant from the Tn4651-related transposon, Tn4661, indicated that the crossover occurs in the 33-bp inverted repeat region, which separates the 136-bp functional rst site into the tnpS- and tnpT-proximal segments. Electrophoretic mobility shift assays demonstrated specific binding of TnpT to the 20-bp inverted repeat region in the tnpT-proximal segment. The requirement for accessory sequences on both sides of the crossover site and the involvement of the unique DNA-binding protein TnpT suggest that the Tn4651-specified resolution system uses a different mechanism than other known resolution systems. Furthermore, comparative sequence analysis for Tn4651-related transposons revealed the occurrence of DNA exchange at the rst site among different transposons, suggesting an additional role of the TnpS-TnpT-rst system in the evolution of Tn4651-related transposons.
Collapse
Affiliation(s)
- Hirokazu Yano
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan.
| | | | | | | | | | | |
Collapse
|
25
|
Chou HH, Marx CJ. Optimization of gene expression through divergent mutational paths. Cell Rep 2012; 1:133-40. [PMID: 22832162 DOI: 10.1016/j.celrep.2011.12.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Revised: 12/09/2011] [Accepted: 12/15/2011] [Indexed: 11/18/2022] Open
Abstract
Adaptation under similar selective pressure often leads to comparable phenotypes. A longstanding question is whether such phenotypic repeatability entails similar (parallelism) or different genotypic changes (convergence). To better understand this, we characterized mutations that optimized expression of a plasmid-borne metabolic pathway during laboratory evolution of a bacterium. Expressing these pathway genes was essential for growth but came with substantial costs. Starting from overexpression, replicate populations founded by this bacterium all evolved to reduce expression. Despite this phenotypic repetitiveness, the underlying mutational spectrum was highly diverse. Analysis of these plasmid mutations identified three distinct means to modulate gene expression: (1) reducing the gene copy number, (2) lowering transcript stability, and (3) integration of the pathway-bearing plasmid into the host genome. Our study revealed diverse molecular changes beneath convergence to a simple phenotype. This complex genotype-phenotype mapping presents a challenge to inferring genetic evolution based solely on phenotypic changes.
Collapse
Affiliation(s)
- Hsin-Hung Chou
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | | |
Collapse
|
26
|
Roles of endonuclease V, uracil-DNA glycosylase, and mismatch repair in Bacillus subtilis DNA base-deamination-induced mutagenesis. J Bacteriol 2011; 194:243-52. [PMID: 22056936 DOI: 10.1128/jb.06082-11] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The disruption of ung, the unique uracil-DNA-glycosylase-encoding gene in Bacillus subtilis, slightly increased the spontaneous mutation frequency to rifampin resistance (Rif(r)), suggesting that additional repair pathways counteract the mutagenic effects of uracil in this microorganism. An alternative excision repair pathway is involved in this process, as the loss of YwqL, a putative endonuclease V homolog, significantly increased the mutation frequency of the ung null mutant, suggesting that Ung and YwqL both reduce the mutagenic effects of base deamination. Consistent with this notion, sodium bisulfite (SB) increased the Rif(r) mutation frequency of the single ung and double ung ywqL strains, and the absence of Ung and/or YwqL decreased the ability of B. subtilis to eliminate uracil from DNA. Interestingly, the Rif(r) mutation frequency of single ung and mutSL (mismatch repair [MMR] system) mutants was dramatically increased in a ung knockout strain that was also deficient in MutSL, suggesting that the MMR pathway also counteracts the mutagenic effects of uracil. Since the mutation frequency of the ung mutSL strain was significantly increased by SB, in addition to Ung, the mutagenic effects promoted by base deamination in growing B. subtilis cells are prevented not only by YwqL but also by MMR. Importantly, in nondividing cells of B. subtilis, the accumulations of mutations in three chromosomal alleles were significantly diminished following the disruption of ung and ywqL. Thus, under conditions of nutritional stress, the processing of deaminated bases in B. subtilis may normally occur in an error-prone manner to promote adaptive mutagenesis.
Collapse
|
27
|
Lü Z, Wang A. A new experimental system for study on adaptive mutations. ACTA ACUST UNITED AC 2011; 44:58-65. [PMID: 18763089 DOI: 10.1007/bf02882073] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2000] [Indexed: 11/27/2022]
Abstract
A super-repressed mutant of purR (purR(S)), which encodes a repressor protein controlling expression of purine biosynthetic genes inSalmonella typhimurium, grew very slowly on NCE medium with 10 mug/mL Ade and lactose as sole carbon source (cannot form colonies). However, a phenomenon of late-arising mutations was observed when purR(S) mutants were spread on NCE+lactose plates and subjected to a prolonged non-lethal selection. The reconstruction experiments of revertants showed that the late-arising "lac(+)" mutants are not slow growing mutants. Statistical analysis indicated that the distribution of late-arising mutants is Poisson distribution, showing that reversion occurred after plating. The result of co-transductional analysis preliminarily showed that late-arising mutation occurred at selected genepurR or 16 bp PUR box,cis element of structural genepurD. The above results suggest that the phenomenon of late-arising mutation observed by our system is a result of adaptive mutations which are different from random mutations. This is the first time to extend target genes at which adaptive mutations could occur from structural genes involved in carbon metabolism and amino acid biosynthesis totrans regulatory gene coding repressor protein. Our results have provided not only a new proof for generality of adaptive mutations but also a new system for study on adaptive mutations.
Collapse
Affiliation(s)
- Z Lü
- Institute of Microbiology, Chinese Academy of Sciences, 100080, Beijing, China
| | | |
Collapse
|
28
|
Karpinets T, Greenwood D, Pogribny I, Samatova N. Bacterial stationary-state mutagenesis and Mammalian tumorigenesis as stress-induced cellular adaptations and the role of epigenetics. Curr Genomics 2011; 7:481-96. [PMID: 18369407 DOI: 10.2174/138920206779315764] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2006] [Revised: 11/11/2006] [Accepted: 11/23/2006] [Indexed: 01/16/2023] Open
Abstract
Mechanisms of cellular adaptation may have some commonalities across different organisms. Revealing these common mechanisms may provide insight in the organismal level of adaptation and suggest solutions to important problems related to the adaptation. An increased rate of mutations, referred as the mutator phenotype, and beneficial nature of these mutations are common features of the bacterial stationary-state mutagenesis and of the tumorigenic transformations in mammalian cells. We argue that these commonalities of mammalian and bacterial cells result from their stress-induced adaptation that may be described in terms of a common model. Specifically, in both organisms the mutator phenotype is activated in a subpopulation of proliferating stressed cells as a strategy to survival. This strategy is an alternative to other survival strategies, such as senescence and programmed cell death, which are also activated in the stressed cells by different subpopulations. Sustained stress-related proliferative signalling and epigenetic mechanisms play a decisive role in the choice of the mutator phenotype survival strategy in the cells. They reprogram cellular functions by epigenetic silencing of cell-cycle inhibitors, DNA repair, programmed cell death, and by activation of repetitive DNA elements. This reprogramming leads to the mutator phenotype that is implemented by error-prone cell divisions with the involvement of Y family polymerases. Studies supporting the proposed model of stress-induced cellular adaptation are discussed. Cellular mechanisms involved in the bacterial stress-induced adaptation are considered in more detail.
Collapse
Affiliation(s)
- Tv Karpinets
- Computational Biology Institute, Computer Science and Mathematics Division, Oak Ridge National Laboratory, P.O. Box 2008, MS6164, Oak Ridge, TN 37831, USA
| | | | | | | |
Collapse
|
29
|
Pierce A, Gillette D, Jones PG. Escherichia coli cold shock protein CsdA effects an increase in septation and the resultant formation of coccobacilli at low temperature. Arch Microbiol 2011; 193:373-84. [PMID: 21359956 DOI: 10.1007/s00203-011-0682-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Revised: 01/18/2011] [Accepted: 02/04/2011] [Indexed: 02/06/2023]
Abstract
Bacterial shape is controlled by peptidoglycan assembly along the lateral wall and at the septum site. In contrast to rods at 37°C, the wild-type strain formed coccobacilli at 12°C, indicating a prevailing shift toward septal peptidoglycan synthesis at low temperature. Escherichia coli cold shock protein CsdA is a DEAD-box RNA helicase with an extended variable region at the carboxyl terminus. The csdA null mutant formed elongated cells indicating that CsdA, directly or indirectly, effects an increase in septation and the resultant coccobacillus morphology. Lipoprotein NlpI is suggested for a role in cell division. The presence of a plasmid encoding CsdA or NlpI increased septation and coccobacillus morphology of the csdA null mutant cells. Plasmid-encoded CsdAΔ445 (lacking the C-terminal extension) in the mutant complemented the growth and resulted in the appearance of coccobacillus- and rod-shaped cells. In contrast, a plasmid encoding both NlpI and CsdAΔ445 in the wild-type or mutant resulted in inhibition of growth accompanied with the formation of elongated and misshapen cells. However, a plasmid encoding both NlpI and CsdA resulted in normal growth and coccobacilli. The data indicate that the addition of the C-terminal extension yields an increase in septation and the resultant increased formation of coccobacilli.
Collapse
Affiliation(s)
- Ashley Pierce
- Department of Life Sciences, Winston-Salem State University, NC 27110, USA
| | | | | |
Collapse
|
30
|
Mismatch repair modulation of MutY activity drives Bacillus subtilis stationary-phase mutagenesis. J Bacteriol 2010; 193:236-45. [PMID: 20971907 DOI: 10.1128/jb.00940-10] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Stress-promoted mutations that occur in nondividing cells (adaptive mutations) have been implicated strongly in causing genetic variability as well as in species survival and evolutionary processes. Oxidative stress-induced DNA damage has been associated with generation of adaptive His(+) and Met(+) but not Leu(+) revertants in strain Bacillus subtilis YB955 (hisC952 metB5 leuC427). Here we report that an interplay between MutY and MutSL (mismatch repair system [MMR]) plays a pivotal role in the production of adaptive Leu(+) revertants. Essentially, the genetic disruption of MutY dramatically reduced the reversion frequency to the leu allele in this model system. Moreover, the increased rate of adaptive Leu(+) revertants produced by a MutSL knockout strain was significantly diminished following mutY disruption. Interestingly, although the expression of mutY took place during growth and stationary phase and was not under the control of RecA, PerR, or σ(B), a null mutation in the mutSL operon increased the expression of mutY several times. Thus, in starved cells, saturation of the MMR system may induce the expression of mutY, disturbing the balance between MutY and MMR proteins and aiding in the production of types of mutations detected by reversion to leucine prototrophy. In conclusion, our results support the idea that MMR regulation of the mutagenic/antimutagenic properties of MutY promotes stationary-phase mutagenesis in B. subtilis cells.
Collapse
|
31
|
Navarro Llorens JM, Tormo A, Martínez-García E. Stationary phase in gram-negative bacteria. FEMS Microbiol Rev 2010; 34:476-95. [PMID: 20236330 DOI: 10.1111/j.1574-6976.2010.00213.x] [Citation(s) in RCA: 301] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Conditions that sustain constant bacterial growth are seldom found in nature. Oligotrophic environments and competition among microorganisms force bacteria to be able to adapt quickly to rough and changing situations. A particular lifestyle composed of continuous cycles of growth and starvation is commonly referred to as feast and famine. Bacteria have developed many different mechanisms to survive in nutrient-depleted and harsh environments, varying from producing a more resistant vegetative cell to complex developmental programmes. As a consequence of prolonged starvation, certain bacterial species enter a dynamic nonproliferative state in which continuous cycles of growth and death occur until 'better times' come (restoration of favourable growth conditions). In the laboratory, microbiologists approach famine situations using batch culture conditions. The entrance to the stationary phase is a very regulated process governed by the alternative sigma factor RpoS. Induction of RpoS changes the gene expression pattern, aiming to produce a more resistant cell. The study of stationary phase revealed very interesting phenomena such as the growth advantage in stationary phase phenotype. This review focuses on some of the interesting responses of gram-negative bacteria when they enter the fascinating world of stationary phase.
Collapse
|
32
|
Jatsenko T, Tover A, Tegova R, Kivisaar M. Molecular characterization of Rif(r) mutations in Pseudomonas aeruginosa and Pseudomonas putida. Mutat Res 2010; 683:106-114. [PMID: 19887074 DOI: 10.1016/j.mrfmmm.2009.10.015] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Revised: 10/06/2009] [Accepted: 10/23/2009] [Indexed: 05/28/2023]
Abstract
The rpoB gene encoding for beta subunit of RNA polymerase is a target of mutations leading to rifampicin resistant (Rif(r)) phenotype of bacteria. Here we have characterized rpoB/Rif(r) system in Pseudomonas aeruginosa and Pseudomonas putida as a test system for studying mutational processes. We found that in addition to the appearance of large colonies which were clearly visible on Rif selective plates already after 24h of plating, small colonies grew up on these plates for 48 h. The time-dependent appearance of the mutant colonies onto selective plates was caused by different levels of Rif resistance of the mutants. The Rif(r) clusters of the rpoB gene were sequenced and analyzed for 360 mutants of P. aeruginosa and for 167 mutants of P. putida. The spectrum of Rif(r) mutations characterized for P. aeruginosa grown at 37 degrees C and that characterized for P. putida grown at 30 degrees C were dissimilar but the differences almost disappeared when the mutants of both strain were isolated at the same temperature, at 30 degrees C. The strong Rif(r) phenotype of P. aeruginosa and P. putida was accompanied only with substitutions of these residues which belong to the putative Rif-binding pocket. Approximately 70% of P. aeruginosa mutants, which were isolated at 37 degrees C and expressed weak Rif(r) phenotype, contained base substitutions in the N-terminal cluster of the rpoB gene. The differences in the spectra of mutations at 30 degrees C and 37 degrees C can be explained by temperature-sensitive growth of several mutants in the presence of rifampicin. Thus, our results imply that both the temperature for the growth of bacteria and the time for isolation of Rif(r) mutants from selective plates are critical when the rpoB/Rif(r) test system is employed for comparative studies of mutagenic processes in Pseudomonas species which are conventionally cultivated at different temperatures.
Collapse
Affiliation(s)
- Tatjana Jatsenko
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University, Tartu, Estonia
| | | | | | | |
Collapse
|
33
|
Teras R, Jakovleva J, Kivisaar M. Fis negatively affects binding of Tn4652 transposase by out-competing IHF from the left end of Tn4652. MICROBIOLOGY-SGM 2009; 155:1203-1214. [PMID: 19332822 DOI: 10.1099/mic.0.022830-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Transposition activity in bacteria is generally maintained at a low level. The activity of mobile DNA elements can be controlled by bacterially encoded global regulators. Regulation of transposition of Tn4652 in Pseudomonas putida is one such example. Activation of transposition of Tn4652 in starving bacteria requires the stationary-phase sigma factor RpoS and integration host factor (IHF). IHF plays a dual role in Tn4652 translocation by activating transcription of the transposase gene tnpA of the transposon and facilitating TnpA binding to the inverted repeats of the transposon. Our previous results have indicated that besides IHF some other P. putida-encoded global regulator(s) might bind to the ends of Tn4652 and regulate transposition activity. In this study, employing a DNase I footprint assay we have identified a binding site of P. putida Fis (factor for inversion stimulation) centred 135 bp inside the left end of Tn4652. Our results of gel mobility shift and DNase I footprint studies revealed that Fis out-competes IHF from the left end of Tn4652, thereby abolishing the binding of TnpA. Thus, the results obtained in this study indicate that the transposition of Tn4652 is regulated by the cellular amount of P. putida global regulators Fis and IHF.
Collapse
Affiliation(s)
- Riho Teras
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 51010 Tartu, Estonia
| | - Julia Jakovleva
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 51010 Tartu, Estonia
| | - Maia Kivisaar
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 51010 Tartu, Estonia
| |
Collapse
|
34
|
Fani R, Fondi M. Origin and evolution of metabolic pathways. Phys Life Rev 2009; 6:23-52. [PMID: 20416849 DOI: 10.1016/j.plrev.2008.12.003] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Revised: 11/27/2008] [Accepted: 12/01/2008] [Indexed: 10/21/2022]
Abstract
The emergence and evolution of metabolic pathways represented a crucial step in molecular and cellular evolution. In fact, the exhaustion of the prebiotic supply of amino acids and other compounds that were likely present in the ancestral environment, imposed an important selective pressure, favoring those primordial heterotrophic cells which became capable of synthesizing those molecules. Thus, the emergence of metabolic pathways allowed primitive organisms to become increasingly less-dependent on exogenous sources of organic compounds. Comparative analyses of genes and genomes from organisms belonging to Archaea, Bacteria and Eukarya revealed that, during evolution, different forces and molecular mechanisms might have driven the shaping of genomes and the arisal of new metabolic abilities. Among these gene elongations, gene and operon duplications undoubtedly played a major role since they can lead to the (immediate) appearance of new genetic material that, in turn, might undergo evolutionary divergence giving rise to new genes coding for new metabolic abilities. Gene duplication has been invoked in the different schemes proposed to explain why and how the extant metabolic pathways have arisen and shaped. Both the analysis of completely sequenced genomes and directed evolution experiments strongly support one of them, i.e. the patchwork hypothesis, according to which metabolic pathways have been assembled through the recruitment of primitive enzymes that could react with a wide range of chemically related substrates. However, the analysis of the structure and organization of genes belonging to ancient metabolic pathways, such as histidine biosynthesis and nitrogen fixation, suggested that other different hypothesis, i.e. the retrograde hypothesis or the semi-enzymatic theory, may account for the arisal of some metabolic routes.
Collapse
Affiliation(s)
- Renato Fani
- Laboratory of Microbial and Molecular Evolution, Department of Evolutionary Biology, Via Romana 17-19, University of Florence, Italy
| | | |
Collapse
|
35
|
Defects in the error prevention oxidized guanine system potentiate stationary-phase mutagenesis in Bacillus subtilis. J Bacteriol 2008; 191:506-13. [PMID: 19011023 DOI: 10.1128/jb.01210-08] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Previous studies showed that a Bacillus subtilis strain deficient in mismatch repair (MMR; encoded by the mutSL operon) promoted the production of stationary-phase-induced mutations. However, overexpression of the mutSL operon did not completely suppress this process, suggesting that additional DNA repair mechanisms are involved in the generation of stationary-phase-associated mutants in this bacterium. In agreement with this hypothesis, the results presented in this work revealed that starved B. subtilis cells lacking a functional error prevention GO (8-oxo-G) system (composed of YtkD, MutM, and YfhQ) had a dramatic propensity to increase the number of stationary-phase-induced revertants. These results strongly suggest that the occurrence of mutations is exacerbated by reactive oxygen species in nondividing cells of B. subtilis having an inactive GO system. Interestingly, overexpression of the MMR system significantly diminished the accumulation of mutations in cells deficient in the GO repair system during stationary phase. These results suggest that the MMR system plays a general role in correcting base mispairing induced by oxidative stress during stationary phase. Thus, the absence or depression of both the MMR and GO systems contributes to the production of stationary-phase mutants in B. subtilis. In conclusion, our results support the idea that oxidative stress is a mechanism that generates genetic diversity in starved cells of B. subtilis, promoting stationary-phase-induced mutagenesis in this soil microorganism.
Collapse
|
36
|
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.
Collapse
Affiliation(s)
- Patricia L Foster
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
| |
Collapse
|
37
|
Robleto EA, Yasbin R, Ross C, Pedraza-Reyes M. Stationary phase mutagenesis in B. subtilis: a paradigm to study genetic diversity programs in cells under stress. Crit Rev Biochem Mol Biol 2008; 42:327-39. [PMID: 17917870 DOI: 10.1080/10409230701597717] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
One of the experimental platforms to study programs increasing genetic diversity in cells under stressful or nondividing conditions is adaptive mutagenesis, also called stationary phase mutagenesis or stress-induced mutagenesis. In some model systems, there is evidence that mutagenesis occurs in genes that are actively transcribed. Some of those genes may be actively transcribed as a result of environmental stress giving the appearance of directed mutation. That is, cells under conditions of starvation or other stresses accumulate mutations in transcribed genes, including those transcribed because of the selective pressure. An important question concerns how, within the context of stochastic processes, a cell biases mutation to genes under selection pressure? Because the mechanisms underlying DNA transactions in prokaryotic cells are well conserved among the three domains of life, these studies are likely to apply to the examination of genetic programs in eukaryotes. In eukaryotes, increasing genetic diversity in differentiated cells has been implicated in neoplasia and cell aging. Historically, Escherichia coli has been the paradigm used to discern the cellular processes driving the generation of adaptive mutations; however, examining adaptive mutation in Bacillus subtilis has contributed new insights. One noteworthy contribution is that the B. subtilis' ability to accumulate chromosomal mutations under conditions of starvation is influenced by cell differentiation and transcriptional derepression, as well as by proteins homologous to transcription and repair factors. Here we revise and discuss concepts pertaining to genetic programs that increase diversity in B. subtilis cells under nutritional stress.
Collapse
|
38
|
Galhardo RS, Hastings PJ, Rosenberg SM. Mutation as a stress response and the regulation of evolvability. Crit Rev Biochem Mol Biol 2007; 42:399-435. [PMID: 17917874 PMCID: PMC3319127 DOI: 10.1080/10409230701648502] [Citation(s) in RCA: 398] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Our concept of a stable genome is evolving to one in which genomes are plastic and responsive to environmental changes. Growing evidence shows that a variety of environmental stresses induce genomic instability in bacteria, yeast, and human cancer cells, generating occasional fitter mutants and potentially accelerating adaptive evolution. The emerging molecular mechanisms of stress-induced mutagenesis vary but share telling common components that underscore two common themes. The first is the regulation of mutagenesis in time by cellular stress responses, which promote random mutations specifically when cells are poorly adapted to their environments, i.e., when they are stressed. A second theme is the possible restriction of random mutagenesis in genomic space, achieved via coupling of mutation-generating machinery to local events such as DNA-break repair or transcription. Such localization may minimize accumulation of deleterious mutations in the genomes of rare fitter mutants, and promote local concerted evolution. Although mutagenesis induced by stresses other than direct damage to DNA was previously controversial, evidence for the existence of various stress-induced mutagenesis programs is now overwhelming and widespread. Such mechanisms probably fuel evolution of microbial pathogenesis and antibiotic-resistance, and tumor progression and chemotherapy resistance, all of which occur under stress, driven by mutations. The emerging commonalities in stress-induced-mutation mechanisms provide hope for new therapeutic interventions for all of these processes.
Collapse
Affiliation(s)
- Rodrigo S Galhardo
- Department of Molecular and Human Genetics, Baylor College, Houston, Texas 77030-3411, USA
| | | | | |
Collapse
|
39
|
Tark M, Tover A, Koorits L, Tegova R, Kivisaar M. Dual role of NER in mutagenesis in Pseudomonas putida. DNA Repair (Amst) 2007; 7:20-30. [PMID: 17720631 DOI: 10.1016/j.dnarep.2007.07.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 06/14/2007] [Accepted: 07/16/2007] [Indexed: 11/27/2022]
Abstract
Nucleotide excision repair (NER) is one of the most important repair systems which counteracts different forms of DNA damage either induced by various chemicals or irradiation. At the same time, less is known about the functions of NER in repair of DNA that is not exposed to exogenous DNA-damaging agents. We have investigated the role of NER in mutagenesis in Pseudomonas putida. The genome of this organism contains two uvrA genes, uvrA and uvrA2. Genetic studies on the effects of uvrA, uvrA2, uvrB and UvrC in mutagenic processes revealed that all of these genes are responsible for the repair of UV-induced DNA damage in P. putida. However, uvrA plays more important role in this process than uvrA2 since the deletion of uvrA2 gene had an effect on the UV-tolerance of bacteria only in the case when uvrA was also inactivated. Interestingly, the lack of functional uvrB, uvrC or uvrA2 gene reduced the frequency of stationary-phase mutations. The contribution of uvrA2, uvrB and uvrC to the mutagenesis appeared to be most significant in the case of 1-bp deletions whose emergence is dependent on error-prone DNA polymerase Pol IV. These data imply that NER has a dual role in mutagenesis in P. putida-besides functioning in repair of damaged DNA, NER is also important in generation of mutations. We hypothesize that NER enzymes may initiate gratuitous DNA repair and the following DNA repair synthesis might be mutagenic.
Collapse
Affiliation(s)
- Mariliis Tark
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 23 Riia Street, 51010 Tartu, Estonia
| | | | | | | | | |
Collapse
|
40
|
Saumaa S, Tover A, Tark M, Tegova R, Kivisaar M. Oxidative DNA damage defense systems in avoidance of stationary-phase mutagenesis in Pseudomonas putida. J Bacteriol 2007; 189:5504-14. [PMID: 17545288 PMCID: PMC1951809 DOI: 10.1128/jb.00518-07] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Oxidative damage of DNA is a source of mutation in living cells. Although all organisms have evolved mechanisms of defense against oxidative damage, little is known about these mechanisms in nonenteric bacteria, including pseudomonads. Here we have studied the involvement of oxidized guanine (GO) repair enzymes and DNA-protecting enzyme Dps in the avoidance of mutations in starving Pseudomonas putida. Additionally, we examined possible connections between the oxidative damage of DNA and involvement of the error-prone DNA polymerase (Pol)V homologue RulAB in stationary-phase mutagenesis in P. putida. Our results demonstrated that the GO repair enzymes MutY, MutM, and MutT are involved in the prevention of base substitution mutations in carbon-starved P. putida. Interestingly, the antimutator effect of MutT was dependent on the growth phase of bacteria. Although the lack of MutT caused a strong mutator phenotype under carbon starvation conditions for bacteria, only a twofold increased effect on the frequency of mutations was observed for growing bacteria. This indicates that MutT has a backup system which efficiently complements the absence of this enzyme in actively growing cells. The knockout of MutM affected only the spectrum of mutations but did not change mutation frequency. Dps is known to protect DNA from oxidative damage. We found that dps-defective P. putida cells were more sensitive to sudden exposure to hydrogen peroxide than wild-type cells. At the same time, the absence of Dps did not affect the accumulation of mutations in populations of starved bacteria. Thus, it is possible that the protective role of Dps becomes essential for genome integrity only when bacteria are exposed to exogenous agents that lead to oxidative DNA damage but not under physiological conditions. Introduction of the Y family DNA polymerase PolV homologue rulAB into P. putida increased the proportion of A-to-C and A-to-G base substitutions among mutations, which occurred under starvation conditions. Since PolV is known to perform translesion synthesis past damaged bases in DNA (e.g., some oxidized forms of adenine), our results may imply that adenine oxidation products are also an important source of mutation in starving bacteria.
Collapse
Affiliation(s)
- Signe Saumaa
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 23 Riia Street, 51010 Tartu, Estonia
| | | | | | | | | |
Collapse
|
41
|
Kivistik PA, Kivisaar M, Hõrak R. Target site selection of Pseudomonas putida transposon Tn4652. J Bacteriol 2007; 189:3918-21. [PMID: 17351034 PMCID: PMC1913344 DOI: 10.1128/jb.01863-06] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We analyzed the target preferences of a Tn3 family transposon Tn4652. Alignment of 93 different insertion sites revealed a consensus sequence which resembles that of Tn3, indicating that despite a low similarity between Tn4652 and Tn3 transposases, their target site recognition is conserved.
Collapse
Affiliation(s)
- Paula Ann Kivistik
- Estonian Biocentre and Institute of Molecular and Cell Biology, Tartu University, 51010 Tartu, Estonia
| | | | | |
Collapse
|
42
|
Saumaa S, Tarassova K, Tark M, Tover A, Tegova R, Kivisaar M. Involvement of DNA mismatch repair in stationary-phase mutagenesis during prolonged starvation of Pseudomonas putida. DNA Repair (Amst) 2006; 5:505-14. [PMID: 16414311 DOI: 10.1016/j.dnarep.2005.12.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Revised: 12/05/2005] [Accepted: 12/05/2005] [Indexed: 11/21/2022]
Abstract
One of the popular ideas is that decline in methyl-directed mismatch repair (MMR) in carbon-starved bacteria might facilitate occurrence of stationary-phase mutations. We compared the frequency of accumulation of stationary-phase mutations in carbon-starved Pseudomonas putida wild-type and MMR-defective strains and found that knockout of MMR system increased significantly emergence of base substitutions in starving P. putida. At the same time, the appearance of 1-bp deletion mutations was less affected by MMR in this bacterium. The spectrum of base substitution mutations which occurred in starving populations of P. putida wild-type strain was distinct from mutation spectrum identified in MMR-defective strains. The spectrum of base substitutions differed also in this case when mutants emerged in starved populations of MutS or MutL-defective strains were comparatively analyzed. Based on our results we suppose that other mechanisms than malfunctioning of MMR system in resting cells might be considered to explain the accumulation of stationary-phase mutations in P. putida. To further characterize populations of P. putida starved on selective plates, we stained bacteria with LIVE/DEAD kit in situ on agar plates. We found that although the overall number of colony forming units (CFU) did not decline in long-term-starved populations, these populations were very heterogeneous on the plates and contained many dead cells. Our results imply that slow growth of subpopulation of cells at the expenses of dead cells on selective plates might be important for the generation of stationary-phase mutations in P. putida. Additionally, the different survival patterns of P. putida on the same selective plates hint that competitive interactions taking place under conditions of prolonged starvation of microbial populations on semi-solid surfaces might be more complicated than previously assumed.
Collapse
Affiliation(s)
- Signe Saumaa
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 23 Riia Street, 51010 Tartu, Estonia
| | | | | | | | | | | |
Collapse
|
43
|
Hõrak R, Ilves H, Pruunsild P, Kuljus M, Kivisaar M. The ColR-ColS two-component signal transduction system is involved in regulation of Tn4652 transposition in Pseudomonas putida under starvation conditions. Mol Microbiol 2005; 54:795-807. [PMID: 15491368 DOI: 10.1111/j.1365-2958.2004.04311.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bacteria use two-component signal transduction pathways to sense both extracellular and intracellular environment and to coordinate cellular events according to changing conditions. Adaptation can be either physiological or genetical. Here, we present evidence that a genome reorganization process such as transposition can be controlled by certain environmental cues sensed by a two-component signal transduction system. We demonstrate that transposition-dependent accumulation of phenol-utilizing mutants is severely decreased in Pseudomonas putida defective in a two-component system colRS. Translocation of Tn4652 is decreased both in colR- and colS-defective strains, indicating that signal transduction from a histidine kinase ColS to a response regulator ColR is necessary for the activation of Tn4652 in bacteria starving on phenol. However, overexpression of ColR in a colS-defective strain restores Tn4652 transposition, suggesting that absence of the signal from ColS can be compensated by an elevated amount of ColR. In vitro analysis of purified ColR and ColS proteins evidenced that they constitute a functional phosphorelay. Site-directed mutagenesis revealed that a conserved H221 can be the phosphoryl-accepting residue in ColS and that aspartate residues D8 and D51 of ColR are necessary for the phosphotransfer from ColS to ColR. To our knowledge, Tn4652 is the first bacterial transposon regulated by a two-component system. This finding indicates that transpositional activity can respond to signals sensed and processed by the host.
Collapse
Affiliation(s)
- Rita Hõrak
- Estonian Biocentre and Institute of Molecular and Cell Biology, Tartu University, 51010 Tartu, Estonia.
| | | | | | | | | |
Collapse
|
44
|
Pedraza-Reyes M, Yasbin RE. Contribution of the mismatch DNA repair system to the generation of stationary-phase-induced mutants of Bacillus subtilis. J Bacteriol 2004; 186:6485-91. [PMID: 15375129 PMCID: PMC516593 DOI: 10.1128/jb.186.19.6485-6491.2004] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A reversion assay system previously implemented to demonstrate the existence of adaptive or stationary-phase-induced mutagenesis in Bacillus subtilis was utilized in this report to study the influence of the mismatch DNA repair (MMR) system on this type of mutagenesis. Results revealed that a strain deficient in MutSL showed a significant propensity to generate increased numbers of stationary-phase-induced revertants. These results suggest that absence or depression of MMR is an important factor in the mutagenesis of nongrowing B. subtilis cells because of the role of MMR in repairing DNA damage. In agreement with this suggestion, a significant decrease in the number of adaptive revertant colonies, for the three markers tested, occurred in B. subtilis cells which overexpressed a component of the MMR system. Interestingly, the single overexpression of mutS, but not of mutL, was sufficient to decrease the level of adaptive mutants in the reversion assay system of B. subtilis. The results presented in this work, as well as in our previous studies, appear to suggest that an MMR deficiency, putatively attributable to inactivation or saturation with DNA damage of MutS, may occur in a subset of B. subtilis cells that differentiate into the hypermutable state.
Collapse
Affiliation(s)
- Mario Pedraza-Reyes
- Institute of Investigation in Experimental Biology, Faculty of Chemistry, University of Guanajuato, Guanajuato, Mexico
| | | |
Collapse
|
45
|
Amzallag GN. Adaptive changes in bacteria: a consequence of nonlinear transitions in chromosome topology? J Theor Biol 2004; 229:361-9. [PMID: 15234203 DOI: 10.1016/j.jtbi.2004.04.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2003] [Revised: 01/11/2004] [Accepted: 04/06/2004] [Indexed: 10/26/2022]
Abstract
Adaptive changes in bacteria are generally considered to result from random mutations selected by the environment. This interpretation is challenged by the non-randomness of genomic changes observed following ageing or starvation in bacterial colonies. A theory of adaptive targeting of sequences for enzymes involved in DNA transactions is proposed here. It is assumed that the sudden leakage of cAMP consecutive to starvation induces a rapid drop in the ATP/ADP ratio that inactivates the homeostasis in control of the level of DNA supercoiling. This phase change enables the emergence of local modifications in chromosome topology in relation to the missing metabolites, a first stage in expression of an adaptive status in which DNA transactions are induced. The nonlinear perspective proposed here is homologous to that already suggested for adaptation of pluricellular organisms during their development. In both cases, phases of robustness in regulation networks for genetic expression are interspaced by critical periods of breakdown of the homeostatic regulations during which, through isolation of nodes from a whole network, specific changes with adaptive value may locally occur.
Collapse
Affiliation(s)
- G N Amzallag
- The Judea Center for Research and Development, Carmel 90404, Israel.
| |
Collapse
|
46
|
Ilves H, Hõrak R, Teras R, Kivisaar M. IHF is the limiting host factor in transposition of Pseudomonas putida transposon Tn4652 in stationary phase. Mol Microbiol 2004; 51:1773-85. [PMID: 15009901 DOI: 10.1111/j.1365-2958.2003.03948.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Transpositional activity of mobile elements is not constant. Conditional regulation of host factors involved in transposition may severely change the activity of mobile elements. We have demonstrated previously that transposition of Tn4652 in Pseudomonas putida is a stationary phase-specific event, which requires functional sigma S (Ilves et al., 2001, J Bacteriol 183: 5445-5448). We hypothesized that integration host factor (IHF), the concentration of which is increased in starving P. putida, might contribute to the transposition of Tn4652 as well. Here, we demonstrate that transposition of Tn4652 in stationary phase P. putida is essentially limited by the amount of IHF. No transposition of Tn4652 occurs in a P. putida ihfA-defective strain. Moreover, overexpression of IHF results in significant enhancement of transposition compared with the wild-type strain. This indicates that the amount of IHF is a bottleneck in Tn4652 transposition. Gel mobility shift and DNase I footprinting studies revealed that IHF is necessary for the binding of transposase to both transposon ends. In vitro, transposase can bind to inverted repeats of transposon only after the binding of IHF. The results obtained in this study indicate that, besides sigma S, IHF is another host factor that is implicated in the elevation of transposition in stationary phase.
Collapse
Affiliation(s)
- Heili Ilves
- Estonian Biocentre and Institute of Molecular and Cell Biology, Tartu University, 23 Riia Street, 51010 Tartu, Estonia
| | | | | | | |
Collapse
|
47
|
Tegova R, Tover A, Tarassova K, Tark M, Kivisaar M. Involvement of error-prone DNA polymerase IV in stationary-phase mutagenesis in Pseudomonas putida. J Bacteriol 2004; 186:2735-44. [PMID: 15090515 PMCID: PMC387815 DOI: 10.1128/jb.186.9.2735-2744.2004] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2003] [Accepted: 01/23/2004] [Indexed: 11/20/2022] Open
Abstract
In this work we studied involvement of DNA polymerase IV (Pol IV) (encoded by the dinB gene) in stationary-phase mutagenesis in Pseudomonas putida. For this purpose we constructed a novel set of assay systems that allowed detection of different types of mutations (e.g., 1-bp deletions and different base substitutions) separately. A significant effect of Pol IV became apparent when the frequency of accumulation of 1-bp deletion mutations was compared in the P. putida wild-type strain and its Pol IV-defective dinB knockout derivative. Pol IV-dependent mutagenesis caused a remarkable increase (approximately 10-fold) in the frequency of accumulation of 1-bp deletion mutations on selective plates in wild-type P. putida populations starved for more than 1 week. No effect of Pol IV on the frequency of accumulation of base substitution mutations in starving P. putida cells was observed. The occurrence of 1-bp deletions in P. putida cells did not require a functional RecA protein. RecA independence of Pol IV-associated mutagenesis was also supported by data showing that transcription from the promoter of the P. putida dinB gene was not significantly influenced by the DNA damage-inducing agent mitomycin C. Therefore, we hypothesize that mechanisms different from the classical RecA-dependent SOS response could elevate Pol IV-dependent mutagenesis in starving P. putida cells.
Collapse
Affiliation(s)
- Radi Tegova
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 23 Riia Street, 51010 Tartu, Estonia
| | | | | | | | | |
Collapse
|
48
|
McAdams HH, Srinivasan B, Arkin AP. The evolution of genetic regulatory systems in bacteria. Nat Rev Genet 2004; 5:169-78. [PMID: 14970819 DOI: 10.1038/nrg1292] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Harley H McAdams
- Department of Developmental Biology, Stanford University School of Medicine, B300 Beckman Center, Stanford, California 94305, USA.
| | | | | |
Collapse
|
49
|
Abstract
Comparative biochemistry demonstrates that the metabolites, complex biochemical networks, enzymes and regulatory mechanisms essential to all living cells are conserved in amazing detail throughout evolution. Thus, in order to evolve, an organism must overcome new adverse conditions without creating different but equally dangerous alterations in its ongoing successful metabolic relationship with its environment. Evidence suggests that stable long-term acquisitive evolution results from minor increases in mutation rates of genes related to a particular stress, with minimal disturbance to the balanced and resilient metabolism critical for responding to an unpredictable environment. Microorganisms have evolved specific biochemical feedback mechanisms that direct mutations to genes derepressed by starvation or other stressors in their environment. Transcription of the activated genes creates localized supercoiling and DNA secondary structures with unpaired bases vulnerable to mutation. The resulting mutants provide appropriate variants for selection by the stress involved, thus accelerating evolution with minimal random damage to the genome. This model has successfully predicted mutation frequencies in genes of E. coli and humans. Stressed cells observed in the laboratory over hundreds of generations accumulate mutations that also arise by this mechanism. When this occurs in repair-deficient mutator strains with high rates of random mutation, the specific stress-directed mutations are also enhanced.
Collapse
Affiliation(s)
- Barbara E Wright
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.
| |
Collapse
|
50
|
Kivisaar M. Stationary phase mutagenesis: mechanisms that accelerate adaptation of microbial populations under environmental stress. Environ Microbiol 2004; 5:814-27. [PMID: 14510835 DOI: 10.1046/j.1462-2920.2003.00488.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Microorganisms are exposed to constantly changing environmental conditions. In a growth-restricting environment (e.g. during starvation), mutants arise that are able to take over the population by a process known as stationary phase mutation. Genetic adaptation of a microbial population under environmental stress involves mechanisms that lead to an elevated mutation rate. Under stressful conditions, DNA synthesis may become more erroneous because of the induction of error-prone DNA polymerases, resulting in a situation in which DNA repair systems are unable to cope with increasing amounts of DNA lesions. Transposition may also increase genetic variation. One may ask whether the rate of mutation under stressful conditions is elevated as a result of malfunctioning of systems responsible for accuracy or are there specific mechanisms that regulate the rate of mutations under stress. Evidence for the presence of mutagenic pathways that have probably been evolved to control the mutation rate in a cell will be discussed.
Collapse
Affiliation(s)
- Maia Kivisaar
- Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 51010 Tartu, Estonia.
| |
Collapse
|