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Papkou A, Garcia-Pastor L, Escudero JA, Wagner A. A rugged yet easily navigable fitness landscape. Science 2023; 382:eadh3860. [PMID: 37995212 DOI: 10.1126/science.adh3860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 09/29/2023] [Indexed: 11/25/2023]
Abstract
Fitness landscape theory predicts that rugged landscapes with multiple peaks impair Darwinian evolution, but experimental evidence is limited. In this study, we used genome editing to map the fitness of >260,000 genotypes of the key metabolic enzyme dihydrofolate reductase in the presence of the antibiotic trimethoprim, which targets this enzyme. The resulting landscape is highly rugged and harbors 514 fitness peaks. However, its highest peaks are accessible to evolving populations via abundant fitness-increasing paths. Different peaks share large basins of attraction that render the outcome of adaptive evolution highly contingent on chance events. Our work shows that ruggedness need not be an obstacle to Darwinian evolution but can reduce its predictability. If true in general, the complexity of optimization problems on realistic landscapes may require reappraisal.
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Affiliation(s)
- Andrei Papkou
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - Lucia Garcia-Pastor
- Departamento de Sanidad Animal and VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain
| | - José Antonio Escudero
- Departamento de Sanidad Animal and VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain
| | - Andreas Wagner
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
- Swiss Institute of Bioinformatics, Lausanne, Switzerland
- The Santa Fe Institute, Santa Fe, NM, USA
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2
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Bruger EL, Chubiz LM, Rojas Echenique JI, Renshaw CJ, Espericueta NV, Draghi JA, Marx CJ. Genetic Context Significantly Influences the Maintenance and Evolution of Degenerate Pathways. Genome Biol Evol 2021; 13:6245841. [PMID: 33885815 PMCID: PMC8214414 DOI: 10.1093/gbe/evab082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/19/2021] [Indexed: 11/16/2022] Open
Abstract
Understanding the evolution of novel physiological traits is highly relevant for expanding the characterization and manipulation of biological systems. Acquisition of new traits can be achieved through horizontal gene transfer (HGT). Here, we investigate drivers that promote or deter the maintenance of HGT-driven degeneracy, occurring when processes accomplish identical functions through nonidentical components. Subsequent evolution can optimize newly acquired functions; for example, beneficial alleles identified in an engineered Methylorubrum extorquens strain allowed it to utilize a “Foreign” formaldehyde oxidation pathway substituted for its Native pathway for methylotrophic growth. We examined the fitness consequences of interactions between these alleles when they were combined with the Native pathway or both (Dual) pathways. Unlike the Foreign pathway context where they evolved, these alleles were often neutral or deleterious when moved into these alternative genetic backgrounds. However, there were instances where combinations of multiple alleles resulted in higher fitness outcomes than individual allelic substitutions could provide. Importantly, the genetic context accompanying these allelic substitutions significantly altered the fitness landscape, shifting local fitness peaks and restricting the set of accessible evolutionary trajectories. These findings highlight how genetic context can negatively impact the probability of maintaining native and HGT-introduced functions together, making it difficult for degeneracy to evolve. However, in cases where the cost of maintaining degeneracy was mitigated by adding evolved alleles impacting the function of these pathways, we observed rare opportunities for pathway coevolution to occur. Together, our results highlight the importance of genetic context and resulting epistasis in retaining or losing HGT-acquired degenerate functions.
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Affiliation(s)
- Eric L Bruger
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, USA.,Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, Idaho, USA.,Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, Idaho, USA.,The BEACON Center for the Study of Evolution in Action, University of Idaho, Moscow, Idaho, USA
| | - Lon M Chubiz
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA.,Department of Biology, University of Missouri, St. Louis, Missouri, USA
| | - José I Rojas Echenique
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA.,Department of Molecular Genetics, University of Toronto, Ontario, Canada
| | - Caleb J Renshaw
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, USA.,Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, Idaho, USA
| | - Nora Victoria Espericueta
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, USA.,Department of Biological Sciences, California State University, Long Beach, California, USA
| | - Jeremy A Draghi
- Department of Biological Sciences, Virginia Institute of Technology, Blacksburg, Virginia, USA
| | - Christopher J Marx
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, USA.,Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, Idaho, USA.,Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, Idaho, USA.,The BEACON Center for the Study of Evolution in Action, University of Idaho, Moscow, Idaho, USA.,Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA
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3
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Yuan XJ, Chen WJ, Ma ZX, Yuan QQ, Zhang M, He L, Mo XH, Zhang C, Zhang CT, Wang MY, Xing XH, Yang S. Rewiring the native methanol assimilation metabolism by incorporating the heterologous ribulose monophosphate cycle into Methylorubrum extorquens. Metab Eng 2021; 64:95-110. [PMID: 33493644 DOI: 10.1016/j.ymben.2021.01.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Revised: 01/05/2021] [Accepted: 01/18/2021] [Indexed: 10/22/2022]
Abstract
Methanol is assimilated through the serine cycle to generate acetyl-CoA without carbon loss. However, a highly active serine cycle requires high consumption of reducing equivalents and ATP, thereby leading to the impaired efficiency of methanol conversion to reduced chemicals. In the present study, a genome-scale flux balance analysis (FBA) predicted that the introduction of the heterologous ribulose monophosphate (RuMP) cycle, a more energy-efficient pathway for methanol assimilation, could theoretically increase growth rate by 31.3% for the model alphaproteobacterial methylotroph Methylorubrum extorquens AM1. Based on this analysis, we constructed a novel synergistic assimilation pathway in vivo by incorporating the RuMP cycle into M. extroquens metabolism with the intrinsic serine cycle. We demonstrated that the operation of the synergistic pathway could increase cell growth rate by 16.5% and methanol consumption rate by 13.1%. This strategy rewired the central methylotrophic metabolism through adjusting core gene transcription, leading to a pool size increase of C2 to C5 central intermediates by 1.2- to 3.6-fold and an NADPH cofactor improvement by 1.3-fold. The titer of 3-hydroxypropionic acid (3-HP), a model product in the newly engineered chassis of M. extorquens AM1, was increased to 91.2 mg/L in shake-flask culture, representing a 3.1-fold increase compared with the control strain with only the serine cycle. The final titer of 3-HP was significantly improved to 0.857 g/L in the fed-batch bioreactor, which was more competitive compared with the other 3-HP producers using methane and CO2 as C1 sources. Collectively, our current study demonstrated that engineering the synergistic methanol assimilation pathway was a promising strategy to increase the carbon assimilation and the yields of reduced chemicals in diverse host strains for C1 microbial cell factories.
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Affiliation(s)
- Xiao-Jie Yuan
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China; Department of Molecular Biology, Qingdao Vland Biotech Inc., Qingdao, Shandong Province, People's Republic of China
| | - Wen-Jing Chen
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Zeng-Xin Ma
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Qian-Qian Yuan
- Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, People's Republic of China
| | - Min Zhang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Lian He
- Department of Chemical Engineering, University of Washington, Seattle, WA, USA
| | - Xu-Hua Mo
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Chong Zhang
- Key Laboratory of Industrial Biocatalysis, Ministry of Education, Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China; Center for Synthetic and Systems Biology, Tsinghua University, Beijing, People's Republic of China
| | - Chang-Tai Zhang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Meng-Ying Wang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Xin-Hui Xing
- Key Laboratory of Industrial Biocatalysis, Ministry of Education, Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China; Center for Synthetic and Systems Biology, Tsinghua University, Beijing, People's Republic of China; Institute of Biopharmaceutical and Health Engineering, Tsinghua Shenzhen International Graduate School, And Institute of Biomedical Health Technology and Engineering, Shenzhen Bay Laboratory, Shenzhen, China
| | - Song Yang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, And Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China; Key Laboratory of Systems Bioengineering, Ministry of Education, Tianjin University, Tianjin, People's Republic of China.
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4
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Acetate and glycerol are not uniquely suited for the evolution of cross-feeding in E. coli. PLoS Comput Biol 2020; 16:e1008433. [PMID: 33253183 PMCID: PMC7728234 DOI: 10.1371/journal.pcbi.1008433] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 12/10/2020] [Accepted: 10/10/2020] [Indexed: 01/26/2023] Open
Abstract
The evolution of cross-feeding among individuals of the same species can help generate genetic and phenotypic diversity even in completely homogeneous environments. Cross-feeding Escherichia coli strains, where one strain feeds on a carbon source excreted by another strain, rapidly emerge during experimental evolution in a chemically minimal environment containing glucose as the sole carbon source. Genome-scale metabolic modeling predicts that cross-feeding of 58 carbon sources can emerge in the same environment, but only cross-feeding of acetate and glycerol has been experimentally observed. Here we use metabolic modeling to ask whether acetate and glycerol cross-feeding are especially likely to evolve, perhaps because they require less metabolic change, and thus perhaps also less genetic change than other cross-feeding interactions. However, this is not the case. The minimally required metabolic changes required for acetate and glycerol cross feeding affect dozens of chemical reactions, multiple biochemical pathways, as well as multiple operons or regulons. The complexity of these changes is consistent with experimental observations, where cross-feeding strains harbor multiple mutations. The required metabolic changes are also no less complex than those observed for multiple other of the 56 cross feeding interactions we study. We discuss possible reasons why only two cross-feeding interactions have been discovered during experimental evolution and argue that multiple new cross-feeding interactions may await discovery. The evolution of cross-feeding interactions, where one organism thrives by consuming the excretions of others, can create diversity even in simple and homogeneous environments. In past work, we had predicted that 58 cross-feeding interactions could evolve in populations of E. coli grown in glucose minimal media, yet only two have been experimentally observed, those involving acetate and glycerol. We hypothesized that multiple mutations might be required for the evolution of computationally predicted but not experimentally observed cross-feeding interactions. To answer this question, we developed a method that searches for the minimal number of metabolic changes required for individuals to change their metabolic state (from an ancestral glucose-consuming state to an evolved state that produces or consumes other metabolite). We observed that the metabolic changes required for the evolution of acetate and glycerol cross-feeding are no less complex than those required for the evolution of the other predicted cross-feeding interactions, which suggests that multiple cross-feeding interactions may still await discovery.
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5
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Roszczenko-Jasińska P, Vu HN, Subuyuj GA, Crisostomo RV, Cai J, Lien NF, Clippard EJ, Ayala EM, Ngo RT, Yarza F, Wingett JP, Raghuraman C, Hoeber CA, Martinez-Gomez NC, Skovran E. Gene products and processes contributing to lanthanide homeostasis and methanol metabolism in Methylorubrum extorquens AM1. Sci Rep 2020; 10:12663. [PMID: 32728125 PMCID: PMC7391723 DOI: 10.1038/s41598-020-69401-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 07/09/2020] [Indexed: 11/08/2022] Open
Abstract
Lanthanide elements have been recently recognized as "new life metals" yet much remains unknown regarding lanthanide acquisition and homeostasis. In Methylorubrum extorquens AM1, the periplasmic lanthanide-dependent methanol dehydrogenase XoxF1 produces formaldehyde, which is lethal if allowed to accumulate. This property enabled a transposon mutagenesis study and growth studies to confirm novel gene products required for XoxF1 function. The identified genes encode an MxaD homolog, an ABC-type transporter, an aminopeptidase, a putative homospermidine synthase, and two genes of unknown function annotated as orf6 and orf7. Lanthanide transport and trafficking genes were also identified. Growth and lanthanide uptake were measured using strains lacking individual lanthanide transport cluster genes, and transmission electron microscopy was used to visualize lanthanide localization. We corroborated previous reports that a TonB-ABC transport system is required for lanthanide incorporation to the cytoplasm. However, cells were able to acclimate over time and bypass the requirement for the TonB outer membrane transporter to allow expression of xoxF1 and growth. Transcriptional reporter fusions show that excess lanthanides repress the gene encoding the TonB-receptor. Using growth studies along with energy dispersive X-ray spectroscopy and transmission electron microscopy, we demonstrate that lanthanides are stored as cytoplasmic inclusions that resemble polyphosphate granules.
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Affiliation(s)
- Paula Roszczenko-Jasińska
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, USA
- Institute of Microbiology, University of Warsaw, Warsaw, Poland
| | - Huong N Vu
- Department of Biological Sciences, San José State University, San José, CA, USA
- Department of Microbiology, University of Georgia, Athens, GA, USA
| | - Gabriel A Subuyuj
- Department of Biological Sciences, San José State University, San José, CA, USA
- Department of Microbiology and Molecular Genetics, University of California At Davis, Davis, CA, USA
| | - Ralph Valentine Crisostomo
- Department of Biological Sciences, San José State University, San José, CA, USA
- Molecular Biology Institute, University of California At Los Angeles, Los Angeles, CA, USA
| | - James Cai
- Department of Biological Sciences, San José State University, San José, CA, USA
| | - Nicholas F Lien
- Department of Biological Sciences, San José State University, San José, CA, USA
| | - Erik J Clippard
- Department of Biological Sciences, San José State University, San José, CA, USA
| | - Elena M Ayala
- Department of Biological Sciences, San José State University, San José, CA, USA
| | - Richard T Ngo
- Department of Biological Sciences, San José State University, San José, CA, USA
| | - Fauna Yarza
- Department of Biological Sciences, San José State University, San José, CA, USA
- Department of Biochemistry and Biophysics, University of California At San Francisco, San Francisco, CA, USA
| | - Justin P Wingett
- Department of Biological Sciences, San José State University, San José, CA, USA
| | | | - Caitlin A Hoeber
- Department of Biological Sciences, San José State University, San José, CA, USA
| | - Norma C Martinez-Gomez
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, USA.
- Department of Plant and Microbial Biology, University of California-Berkeley, Berkeley, California, USA.
| | - Elizabeth Skovran
- Department of Biological Sciences, San José State University, San José, CA, USA.
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6
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Mo XH, Zhang H, Wang TM, Zhang C, Zhang C, Xing XH, Yang S. Establishment of CRISPR interference in Methylorubrum extorquens and application of rapidly mining a new phytoene desaturase involved in carotenoid biosynthesis. Appl Microbiol Biotechnol 2020; 104:4515-4532. [PMID: 32215707 DOI: 10.1007/s00253-020-10543-w] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 03/02/2020] [Accepted: 03/11/2020] [Indexed: 02/04/2023]
Abstract
The methylotrophic bacterium Methylorubrum extorquens AM1 holds a great potential of a microbial cell factory in producing high value chemicals with methanol as the sole carbon and energy source. However, many gene functions remain unknown, hampering further rewiring of metabolic networks. Clustered regularly interspaced short palindromic repeat interference (CRISPRi) has been demonstrated to be a robust tool for gene knockdown in diverse organisms. In this study, we developed an efficient CRISPRi system through optimizing the promoter strength of Streptococcus pyogenes-derived deactivated cas9 (dcas9). When the dcas9 and sgRNA were respectively controlled by medium PR/tetO and strong PmxaF-g promoters, dynamic repression efficacy of cell growth through disturbing a central metabolism gene glyA was achieved from 41.9 to 96.6% dependent on the sgRNA targeting sites. Furthermore, the optimized CRISPRi system was shown to effectively decrease the abundance of exogenous fluorescent protein gene mCherry over 50% and to reduce the expression of phytoene desaturase gene crtI by 97.7%. We then used CRISPRi technology combined with 26 sgRNAs pool to rapidly discover a new phytoene desaturase gene META1_3670 from 2470 recombinant mutants. The gene function was further verified through gene deletion and complementation as well as phylogenetic tree analysis. In addition, we applied CRISPRi to repress the transcriptional level of squalene-hopene cyclase gene shc involved in hopanoid biosynthesis by 64.9%, which resulted in enhancing 1.9-fold higher of carotenoid production without defective cell growth. Thus, the CRISPRi system developed here provides a useful tool in mining functional gene of M. extorquens as well as in biotechnology for producing high-valued chemicals from methanol. KEY POINTS: Developing an efficient CRISPRi to knockdown gene expression in C1-utilizing bacteria CRISPRi combined with sgRNAs pool to rapidly discover a new phytoene desaturase gene Improvement of carotenoid production by repressing a competitive pathway.
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Affiliation(s)
- Xu-Hua Mo
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Hui Zhang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Tian-Min Wang
- Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China
| | - Chong Zhang
- Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China
| | - Cong Zhang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China
| | - Xin-Hui Xing
- Department of Chemical Engineering, Tsinghua University, Beijing, People's Republic of China
| | - Song Yang
- School of Life Sciences, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao Agricultural University, Qingdao, Shandong Province, People's Republic of China.
- Key Laboratory of Systems Bioengineering, Ministry of Education, Tianjin University, Tianjin, People's Republic of China.
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7
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Ferreira C, Bogas D, Bikarolla SK, Varela AR, Frykholm K, Linheiro R, Nunes OC, Westerlund F, Manaia CM. Genetic variation in the conjugative plasmidome of a hospital effluent multidrug resistant Escherichia coli strain. CHEMOSPHERE 2019; 220:748-759. [PMID: 30611073 DOI: 10.1016/j.chemosphere.2018.12.130] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 11/23/2018] [Accepted: 12/18/2018] [Indexed: 06/09/2023]
Abstract
Bacteria harboring conjugative plasmids have the potential for spreading antibiotic resistance through horizontal gene transfer. It is described that the selection and dissemination of antibiotic resistance is enhanced by stressors, like metals or antibiotics, which can occur as environmental contaminants. This study aimed at unveiling the composition of the conjugative plasmidome of a hospital effluent multidrug resistant Escherichia coli strain (H1FC54) under different mating conditions. To meet this objective, plasmid pulsed field gel electrophoresis, optical mapping analyses and DNA sequencing were used in combination with phenotype analysis. Strain H1FC54 was observed to harbor five plasmids, three of which were conjugative and two of these, pH1FC54_330 and pH1FC54_140, contained metal and antibiotic resistance genes. Transconjugants obtained in the absence or presence of tellurite (0.5 μM or 5 μM), arsenite (0.5 μM, 5 μM or 15 μM) or ceftazidime (10 mg/L) and selected in the presence of sodium azide (100 mg/L) and tetracycline (16 mg/L) presented distinct phenotypes, associated with the acquisition of different plasmid combinations, including two co-integrate plasmids, of 310 kbp and 517 kbp. The variable composition of the conjugative plasmidome, the formation of co-integrates during conjugation, as well as the transfer of non-transferable plasmids via co-integration, and the possible association between antibiotic, arsenite and tellurite tolerance was demonstrated. These evidences bring interesting insights into the comprehension of the molecular and physiological mechanisms that underlie antibiotic resistance propagation in the environment.
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Affiliation(s)
- Catarina Ferreira
- Universidade Católica Portuguesa, CBQF - Centro de Biotecnologia e Química Fina, Laboratório Associado, Escola Superior de Biotecnologia, Rua Arquiteto Lobão Vital, 172, 4200-374, Porto, Portugal
| | - Diana Bogas
- Universidade Católica Portuguesa, CBQF - Centro de Biotecnologia e Química Fina, Laboratório Associado, Escola Superior de Biotecnologia, Rua Arquiteto Lobão Vital, 172, 4200-374, Porto, Portugal
| | - Santosh K Bikarolla
- Division of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivagen 10, SE-412 96, Gothenburg, Sweden
| | - Ana Rita Varela
- Universidade Católica Portuguesa, CBQF - Centro de Biotecnologia e Química Fina, Laboratório Associado, Escola Superior de Biotecnologia, Rua Arquiteto Lobão Vital, 172, 4200-374, Porto, Portugal; LEPABE - Laboratory for Process Engineering, Environment, Biotechnology and Energy, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465, Porto, Portugal
| | - Karolin Frykholm
- Division of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivagen 10, SE-412 96, Gothenburg, Sweden
| | - Raquel Linheiro
- Universidade Católica Portuguesa, CBQF - Centro de Biotecnologia e Química Fina, Laboratório Associado, Escola Superior de Biotecnologia, Rua Arquiteto Lobão Vital, 172, 4200-374, Porto, Portugal
| | - Olga C Nunes
- LEPABE - Laboratory for Process Engineering, Environment, Biotechnology and Energy, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465, Porto, Portugal
| | - Fredrik Westerlund
- Division of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivagen 10, SE-412 96, Gothenburg, Sweden
| | - Célia M Manaia
- Universidade Católica Portuguesa, CBQF - Centro de Biotecnologia e Química Fina, Laboratório Associado, Escola Superior de Biotecnologia, Rua Arquiteto Lobão Vital, 172, 4200-374, Porto, Portugal.
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8
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Dionisio F, Zilhão R, Gama JA. Interactions between plasmids and other mobile genetic elements affect their transmission and persistence. Plasmid 2019; 102:29-36. [DOI: 10.1016/j.plasmid.2019.01.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Revised: 01/24/2019] [Accepted: 01/30/2019] [Indexed: 10/27/2022]
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9
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Harnessing Underground Metabolism for Pathway Development. Trends Biotechnol 2019; 37:29-37. [DOI: 10.1016/j.tibtech.2018.08.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 07/17/2018] [Accepted: 08/06/2018] [Indexed: 01/13/2023]
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10
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Van den Bergh B, Swings T, Fauvart M, Michiels J. Experimental Design, Population Dynamics, and Diversity in Microbial Experimental Evolution. Microbiol Mol Biol Rev 2018; 82:e00008-18. [PMID: 30045954 PMCID: PMC6094045 DOI: 10.1128/mmbr.00008-18] [Citation(s) in RCA: 90] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In experimental evolution, laboratory-controlled conditions select for the adaptation of species, which can be monitored in real time. Despite the current popularity of such experiments, nature's most pervasive biological force was long believed to be observable only on time scales that transcend a researcher's life-span, and studying evolution by natural selection was therefore carried out solely by comparative means. Eventually, microorganisms' propensity for fast evolutionary changes proved us wrong, displaying strong evolutionary adaptations over a limited time, nowadays massively exploited in laboratory evolution experiments. Here, we formulate a guide to experimental evolution with microorganisms, explaining experimental design and discussing evolutionary dynamics and outcomes and how it is used to assess ecoevolutionary theories, improve industrially important traits, and untangle complex phenotypes. Specifically, we give a comprehensive overview of the setups used in experimental evolution. Additionally, we address population dynamics and genetic or phenotypic diversity during evolution experiments and expand upon contributing factors, such as epistasis and the consequences of (a)sexual reproduction. Dynamics and outcomes of evolution are most profoundly affected by the spatiotemporal nature of the selective environment, where changing environments might lead to generalists and structured environments could foster diversity, aided by, for example, clonal interference and negative frequency-dependent selection. We conclude with future perspectives, with an emphasis on possibilities offered by fast-paced technological progress. This work is meant to serve as an introduction to those new to the field of experimental evolution, as a guide to the budding experimentalist, and as a reference work to the seasoned expert.
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Affiliation(s)
- Bram Van den Bergh
- Laboratory of Symbiotic and Pathogenic Interactions, Centre of Microbial and Plant Genetics, KU Leuven-University of Leuven, Leuven, Belgium
- Michiels Lab, Center for Microbiology, VIB, Leuven, Belgium
- Douglas Lab, Department of Entomology, Cornell University, Ithaca, New York, USA
| | - Toon Swings
- Laboratory of Symbiotic and Pathogenic Interactions, Centre of Microbial and Plant Genetics, KU Leuven-University of Leuven, Leuven, Belgium
- Michiels Lab, Center for Microbiology, VIB, Leuven, Belgium
| | - Maarten Fauvart
- Laboratory of Symbiotic and Pathogenic Interactions, Centre of Microbial and Plant Genetics, KU Leuven-University of Leuven, Leuven, Belgium
- Michiels Lab, Center for Microbiology, VIB, Leuven, Belgium
- imec, Leuven, Belgium
| | - Jan Michiels
- Laboratory of Symbiotic and Pathogenic Interactions, Centre of Microbial and Plant Genetics, KU Leuven-University of Leuven, Leuven, Belgium
- Michiels Lab, Center for Microbiology, VIB, Leuven, Belgium
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11
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Rosenberg J, Yeak KC, Commichau FM. A two-step evolutionary process establishes a non-native vitamin B6 pathway in Bacillus subtilis. Environ Microbiol 2017; 20:156-168. [PMID: 29027347 DOI: 10.1111/1462-2920.13950] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 09/22/2017] [Accepted: 09/27/2017] [Indexed: 12/11/2022]
Abstract
Pyridoxal 5'-phosphate (PLP), the most important form of vitamin B6 serves as a cofactor for many proteins. Two alternative pathways for de novo PLP biosynthesis are known: the short deoxy-xylulose-5-phosphate (DXP)-independent pathway, which is present in the Gram-positive model bacterium Bacillus subtilis and the longer DXP-dependent pathway, which has been intensively studied in the Gram-negative model bacterium Escherichia coli. Previous studies revealed that bacteria contain many promiscuous enzymes causing a so-called 'underground metabolism', which can be important for the evolution of novel pathways. Here, we evaluated the potential of B. subtilis to use a truncated non-native DXP-dependent PLP pathway from E. coli for PLP synthesis. Adaptive laboratory evolution experiments revealed that two non-native enzymes catalysing the last steps of the DXP-dependent PLP pathway and two genomic alterations are sufficient to allow growth of vitamin B6 auxotrophic bacteria as rapid as the wild type. Thus, the existence of an underground metabolism in B. subtilis facilitates the generation of a pathway for synthesis of PLP using parts of a non-native vitamin B6 pathway. The introduction of non-native enzymes into a metabolic network and rewiring of native metabolism could be helpful to generate pathways that might be optimized for producing valuable substances.
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Affiliation(s)
- Jonathan Rosenberg
- Department of General Microbiology, Institute for Microbiology and Genetics, Georg-August-University Göttingen, Göttingen, Germany
| | - KahYen C Yeak
- Department of General Microbiology, Institute for Microbiology and Genetics, Georg-August-University Göttingen, Göttingen, Germany
| | - Fabian M Commichau
- Department of General Microbiology, Institute for Microbiology and Genetics, Georg-August-University Göttingen, Göttingen, Germany
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12
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Plague GR, Boodram KS, Dougherty KM, Bregg S, Gilbert DP, Bakshi H, Costa D. Transposable Elements Mediate Adaptive Debilitation of Flagella in Experimental Escherichia coli Populations. J Mol Evol 2017. [PMID: 28646326 DOI: 10.1007/s00239-017-9797-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Although insertion sequence (IS) elements are generally considered genomic parasites, they can mediate adaptive genetic changes in bacterial genomes. We discovered that among 12 laboratory-evolved Escherichia coli populations, three had experienced at least six different IS1-mediated deletions of flagellar genes. These deletions all involved the master flagellar regulator flhDC, and as such completely incapacitate motility. Two lines of evidence strongly suggest that these deletions were adaptive in our evolution experiment: (1) parallel evolution in three independent populations is highly unlikely just by chance, and (2) one of these deletion mutations swept to fixation within ~1000 generations, which is over two million times faster than expected if this deletion was instead selectively neutral and thus evolving by genetic drift. Because flagella are energetically expensive to synthesize and operate, we suspect that debilitating their construction conferred a fitness advantage in our well-stirred evolution experiment. These findings underscore the important role that IS elements can play in mediating adaptive loss-of-function mutations in bacteria.
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Affiliation(s)
- Gordon R Plague
- Department of Biology, State University of New York at Potsdam, Potsdam, NY, 13676, USA.
| | | | - Kevin M Dougherty
- Kellogg Biological Station, Michigan State University, Hickory Corners, MI, USA
| | - Sandar Bregg
- Department of Biology, State University of New York at Potsdam, Potsdam, NY, 13676, USA.,Department of Environmental Health Sciences, School of Public Health, University of Michigan, Ann Arbor, MI, USA
| | - Daniel P Gilbert
- Department of Biology, State University of New York at Potsdam, Potsdam, NY, 13676, USA.,School of Engineering Lab, Clarkson University, Potsdam, NY, USA
| | - Hira Bakshi
- Department of Biology, State University of New York at Potsdam, Potsdam, NY, 13676, USA
| | - Daniel Costa
- Department of Biology, State University of New York at Potsdam, Potsdam, NY, 13676, USA.,Department of Cell Biology, Duke University Medical Center, Durham, NC, USA
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13
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Dormeyer M, Lübke AL, Müller P, Lentes S, Reuß DR, Thürmer A, Stülke J, Daniel R, Brantl S, Commichau FM. Hierarchical mutational events compensate for glutamate auxotrophy of a Bacillus subtilis gltC mutant. ENVIRONMENTAL MICROBIOLOGY REPORTS 2017; 9:279-289. [PMID: 28294562 DOI: 10.1111/1758-2229.12531] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Revised: 03/01/2017] [Accepted: 03/05/2017] [Indexed: 06/06/2023]
Abstract
Glutamate is the major donor of nitrogen for anabolic reactions. The Gram-positive soil bacterium Bacillus subtilis either utilizes exogenously provided glutamate or synthesizes it using the gltAB-encoded glutamate synthase (GOGAT). In the absence of glutamate, the transcription factor GltC activates expression of the GOGAT genes for glutamate production. Consequently, a gltC mutant strain is auxotrophic for glutamate. Using a genetic selection and screening system, we could isolate and differentiate between gltC suppressor mutants in one step. All mutants had acquired the ability to synthesize glutamate, independent of GltC. We identified (i) gain-of-function mutations in the gltR gene, encoding the transcription factor GltR, (ii) mutations in the promoter of the gltAB operon and (iii) massive amplification of the genomic locus containing the gltAB operon. The mutants belonging to the first two classes constitutively expressed the gltAB genes and produced sufficient glutamate for growth. By contrast, mutants that belong to the third class appeared most frequently and solved glutamate limitation by increasing the copy number of the poorly expressed gltAB genes. Thus, glutamate auxotrophy of a B. subtilis gltC mutant can be relieved in multiple ways. Moreover, recombination-dependent amplification of the gltAB genes is the predominant mutational event indicating a hierarchy of mutations.
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Affiliation(s)
- Miriam Dormeyer
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Anastasia L Lübke
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Peter Müller
- Department of Genetics, Bacterial Genetics, Friedrich Schiller University Jena, Philosophenweg 12, Jena, 07743, Germany
| | - Sabine Lentes
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Daniel R Reuß
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Andrea Thürmer
- Department of Genomic and Applied Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Jörg Stülke
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Rolf Daniel
- Department of Genomic and Applied Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
| | - Sabine Brantl
- Department of Genetics, Bacterial Genetics, Friedrich Schiller University Jena, Philosophenweg 12, Jena, 07743, Germany
| | - Fabian M Commichau
- Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany
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14
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Parallel Mutations Result in a Wide Range of Cooperation and Community Consequences in a Two-Species Bacterial Consortium. PLoS One 2016; 11:e0161837. [PMID: 27617746 PMCID: PMC5019393 DOI: 10.1371/journal.pone.0161837] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Accepted: 08/12/2016] [Indexed: 11/25/2022] Open
Abstract
Multi-species microbial communities play a critical role in human health, industry, and waste remediation. Recently, the evolution of synthetic consortia in the laboratory has enabled adaptation to be addressed in the context of interacting species. Using an engineered bacterial consortium, we repeatedly evolved cooperative genotypes and examined both the predictability of evolution and the phenotypes that determine community dynamics. Eight Salmonella enterica serovar Typhimurium strains evolved methionine excretion sufficient to support growth of an Escherichia coli methionine auxotroph, from whom they required excreted growth substrates. Non-synonymous mutations in metA, encoding homoserine trans-succinylase (HTS), were detected in each evolved S. enterica methionine cooperator and were shown to be necessary for cooperative consortia growth. Molecular modeling was used to predict that most of the non-synonymous mutations slightly increase the binding affinity for HTS homodimer formation. Despite this genetic parallelism and trend of increasing protein binding stability, these metA alleles gave rise to a wide range of phenotypic diversity in terms of individual versus group benefit. The cooperators with the highest methionine excretion permitted nearly two-fold faster consortia growth and supported the highest fraction of E. coli, yet also had the slowest individual growth rates compared to less cooperative strains. Thus, although the genetic basis of adaptation was quite similar across independent origins of cooperative phenotypes, quantitative measurements of metabolite production were required to predict either the individual-level growth consequences or how these propagate to community-level behavior.
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15
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Miller CR, Nagel AC, Scott L, Settles M, Joyce P, Wichman HA. Love the one you're with: replicate viral adaptations converge on the same phenotypic change. PeerJ 2016; 4:e2227. [PMID: 27547540 PMCID: PMC4958007 DOI: 10.7717/peerj.2227] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 06/16/2016] [Indexed: 11/21/2022] Open
Abstract
Parallelism is important because it reveals how inherently stochastic adaptation is. Even as we come to better understand evolutionary forces, stochasticity limits how well we can predict evolutionary outcomes. Here we sought to quantify parallelism and some of its underlying causes by adapting a bacteriophage (ID11) with nine different first-step mutations, each with eight-fold replication, for 100 passages. This was followed by whole-genome sequencing five isolates from each endpoint. A large amount of variation arose—281 mutational events occurred representing 112 unique mutations. At least 41% of the mutations and 77% of the events were adaptive. Within wells, populations generally experienced complex interference dynamics. The genome locations and counts of mutations were highly uneven: mutations were concentrated in two regulatory elements and three genes and, while 103 of the 112 (92%) of the mutations were observed in ≤4 wells, a few mutations arose many times. 91% of the wells and 81% of the isolates had a mutation in the D-promoter. Parallelism was moderate compared to previous experiments with this system. On average, wells shared 27% of their mutations at the DNA level and 38% when the definition of parallel change is expanded to include the same regulatory feature or residue. About half of the parallelism came from D-promoter mutations. Background had a small but significant effect on parallelism. Similarly, an analyses of epistasis between mutations and their ancestral background was significant, but the result was mostly driven by four individual mutations. A second analysis of epistasis focused on de novo mutations revealed that no isolate ever had more than one D-promoter mutation and that 56 of the 65 isolates lacking a D-promoter mutation had a mutation in genes D and/or E. We assayed time to lysis in four of these mutually exclusive mutations (the two most frequent D-promoter and two in gene D) across four genetic backgrounds. In all cases lysis was delayed. We postulate that because host cells were generally rare (i.e., high multiplicity of infection conditions developed), selection favored phage that delayed lysis to better exploit their current host (i.e., ‘love the one you’re with’). Thus, the vast majority of wells (at least 64 of 68, or 94%) arrived at the same phenotypic solution, but through a variety of genetic changes. We conclude that answering questions about the range of possible adaptive trajectories, parallelism, and the predictability of evolution requires attention to the many biological levels where the process of adaptation plays out.
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Affiliation(s)
- Craig R Miller
- Center for Modeling Complex Interactions, University of Idaho, Moscow, ID, United States; Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID, United States; Department of Biological Sciences, University of Idaho, Moscow, ID, United States; Department of Mathematics, University of Idaho, Moscow, ID, United States
| | - Anna C Nagel
- Department of Biological Sciences, University of Idaho , Moscow , ID , United States
| | - LuAnn Scott
- Department of Biological Sciences, University of Idaho , Moscow , ID , United States
| | - Matt Settles
- Bioinformatics Core, University of California , Davis , CA , United States
| | - Paul Joyce
- Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID, United States; Department of Mathematics, University of Idaho, Moscow, ID, United States
| | - Holly A Wichman
- Center for Modeling Complex Interactions, University of Idaho, Moscow, ID, United States; Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID, United States; Department of Biological Sciences, University of Idaho, Moscow, ID, United States
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16
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Nayak DD, Agashe D, Lee MC, Marx CJ. Selection Maintains Apparently Degenerate Metabolic Pathways due to Tradeoffs in Using Methylamine for Carbon versus Nitrogen. Curr Biol 2016; 26:1416-26. [PMID: 27212407 DOI: 10.1016/j.cub.2016.04.029] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2015] [Revised: 02/17/2016] [Accepted: 04/11/2016] [Indexed: 01/12/2023]
Abstract
Microorganisms often encode multiple non-orthologous metabolic modules that catalyze the same reaction. However, little experimental evidence actually demonstrates a selective basis for metabolic degeneracy. Many methylotrophs-microorganisms that grow on reduced single-carbon compounds-like Methylobacterium extorquens AM1 encode two routes for methylamine oxidation: the periplasmic methylamine dehydrogenase (MaDH) and the cytoplasmic N-methylglutamate (NMG) pathway. In Methylobacterium extorquens AM1, MaDH is essential for methylamine growth, but the NMG pathway has no known physiological role. Here, we use experimental evolution of two isolates lacking (or incapable of using) MaDH to uncover the physiological challenges that need to be overcome in order to use the NMG pathway for growth on methylamine as a carbon and energy source. Physiological characterization of the evolved isolates revealed regulatory rewiring to increase expression of the NMG pathway and novel mechanisms to mitigate cytoplasmic ammonia buildup. These adaptations led us to infer and validate environmental conditions under which the NMG pathway is advantageous compared to MaDH. The highly expressed MaDH enables rapid growth on high concentrations of methylamine as the primary carbon and energy substrate, whereas the energetically expensive NMG pathway plays a pivotal role during growth with methylamine as the sole nitrogen source, which we demonstrate is especially true under limiting concentrations (<1 mM). Tradeoffs between cellular localization and ammonium toxicity lead to selection for this apparent degeneracy as it is beneficial to facultative methylotrophs that have to switch between using methylamine as a carbon and energy source or just a nitrogen source.
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Affiliation(s)
- Dipti D Nayak
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Deepa Agashe
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Ming-Chun Lee
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Christopher J Marx
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; Department of Biological Sciences, University of Idaho, Moscow, ID 83844, USA; Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID 83844, USA; Center for Modeling Complex Interactions, University of Idaho, Moscow, ID 83844, USA.
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17
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Cui J, Good NM, Hu B, Yang J, Wang Q, Sadilek M, Yang S. Metabolomics Revealed an Association of Metabolite Changes and Defective Growth in Methylobacterium extorquens AM1 Overexpressing ecm during Growth on Methanol. PLoS One 2016; 11:e0154043. [PMID: 27116459 PMCID: PMC4846091 DOI: 10.1371/journal.pone.0154043] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2015] [Accepted: 04/07/2016] [Indexed: 11/18/2022] Open
Abstract
Methylobacterium extorquens AM1 is a facultative methylotroph capable of growth on both single-carbon and multi-carbon compounds. The ethylmalonyl-CoA (EMC) pathway is one of the central assimilatory pathways in M. extorquens during growth on C1 and C2 substrates. Previous studies had shown that ethylmalonyl-CoA mutase functioned as a control point during the transition from growth on succinate to growth on ethylamine. In this study we overexpressed ecm, phaA, mcmAB and found that upregulating ecm by expressing it from the strong constitutive mxaF promoter caused a 27% decrease in growth rate on methanol compared to the strain with an empty vector. Targeted metabolomics demonstrated that most of the central intermediates in the ecm over-expressing strain did not change significantly compared to the control strain; However, poly-β-hydroxybutyrate (PHB) was 4.5-fold lower and 3-hydroxybutyryl-CoA was 1.6-fold higher. Moreover, glyoxylate, a toxic and highly regulated essential intermediate, was determined to be 2.6-fold higher when ecm was overexpressed. These results demonstrated that overexpressing ecm can manipulate carbon flux through the EMC pathway and divert it from the carbon and energy storage product PHB, leading to an accumulation of glyoxylate. Furthermore, untargeted metabolomics discovered two unusual metabolites, alanine (Ala)-meso-diaminopimelic acid (mDAP) and Ala-mDAP-Ala, each over 45-fold higher in the ecm over-expressing strain. These two peptides were also found to be highly produced in a dose-dependent manner when glyoxylate was added to the control strain. Overall, this work has explained a direct association of ecm overexpression with glyoxylate accumulation up to a toxic level, which inhibits cell growth on methanol. This research provides useful insight for manipulating the EMC pathway for efficiently producing high-value chemicals in M. extorquens.
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Affiliation(s)
- Jinyu Cui
- School of Life Science, Qingdao Agricultural University, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao, Shandong Province, China
| | - Nathan M. Good
- Department of Microbiology, University of Washington, Seattle, Washington, United States of America
| | - Bo Hu
- Kemin Industries, KI Research & Development, Des Moines, Iowa, United States of America
| | - Jing Yang
- School of Life Science, Qingdao Agricultural University, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao, Shandong Province, China
| | - Qianwen Wang
- Central Laboratory, Qingdao Agricultural University, Qingdao, Shandong Province, China
| | - Martin Sadilek
- Department of Chemistry, University of Washington, Seattle, Washington, United States of America
| | - Song Yang
- School of Life Science, Qingdao Agricultural University, Shandong Province Key Laboratory of Applied Mycology, and Qingdao International Center on Microbes Utilizing Biogas, Qingdao, Shandong Province, China
- Key Laboratory of Systems Bioengineering, Ministry of Education, Tianjin University, Tianjin, China
- * E-mail:
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18
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Agashe D, Sane M, Phalnikar K, Diwan GD, Habibullah A, Martinez-Gomez NC, Sahasrabuddhe V, Polachek W, Wang J, Chubiz LM, Marx CJ. Large-Effect Beneficial Synonymous Mutations Mediate Rapid and Parallel Adaptation in a Bacterium. Mol Biol Evol 2016; 33:1542-53. [PMID: 26908584 PMCID: PMC4868122 DOI: 10.1093/molbev/msw035] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Contrary to previous understanding, recent evidence indicates that synonymous codon changes may sometimes face strong selection. However, it remains difficult to generalize the nature, strength, and mechanism(s) of such selection. Previously, we showed that synonymous variants of a key enzyme-coding gene (fae) of Methylobacterium extorquens AM1 decreased enzyme production and reduced fitness dramatically. We now show that during laboratory evolution, these variants rapidly regained fitness via parallel yet variant-specific, highly beneficial point mutations in the N-terminal region of fae. These mutations (including four synonymous mutations) had weak but consistently positive impacts on transcript levels, enzyme production, or enzyme activity. However, none of the proposed mechanisms (including internal ribosome pause sites or mRNA structure) predicted the fitness impact of evolved or additional, engineered point mutations. This study shows that synonymous mutations can be fixed through strong positive selection, but the mechanism for their benefit varies depending on the local sequence context.
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Affiliation(s)
- Deepa Agashe
- National Center for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bangalore, India Department of Organismic and Evolutionary Biology, Harvard University
| | - Mrudula Sane
- National Center for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bangalore, India
| | - Kruttika Phalnikar
- National Center for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bangalore, India
| | - Gaurav D Diwan
- National Center for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bangalore, India SASTRA University, Thanjavur, India
| | - Alefiyah Habibullah
- National Center for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bangalore, India
| | | | - Vinaya Sahasrabuddhe
- National Center for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bangalore, India
| | - William Polachek
- Department of Organismic and Evolutionary Biology, Harvard University
| | - Jue Wang
- Department of Organismic and Evolutionary Biology, Harvard University Systems Biology Graduate Program, Harvard University
| | - Lon M Chubiz
- Department of Organismic and Evolutionary Biology, Harvard University
| | - Christopher J Marx
- Department of Organismic and Evolutionary Biology, Harvard University Faculty of Arts and Sciences Center for Systems Biology, Harvard University Department of Biological Sciences, University of Idaho Institute for Bioinformatics and Evolutionary Studies, University of Idaho
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Sonntag F, Kroner C, Lubuta P, Peyraud R, Horst A, Buchhaupt M, Schrader J. Engineering Methylobacterium extorquens for de novo synthesis of the sesquiterpenoid α-humulene from methanol. Metab Eng 2015; 32:82-94. [DOI: 10.1016/j.ymben.2015.09.004] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Revised: 08/28/2015] [Accepted: 09/02/2015] [Indexed: 12/23/2022]
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20
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Laan L, Koschwanez JH, Murray AW. Evolutionary adaptation after crippling cell polarization follows reproducible trajectories. eLife 2015; 4. [PMID: 26426479 PMCID: PMC4630673 DOI: 10.7554/elife.09638] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 09/30/2015] [Indexed: 12/21/2022] Open
Abstract
Cells are organized by functional modules, which typically contain components whose removal severely compromises the module's function. Despite their importance, these components are not absolutely conserved between parts of the tree of life, suggesting that cells can evolve to perform the same biological functions with different proteins. We evolved Saccharomyces cerevisiae for 1000 generations without the important polarity gene BEM1. Initially the bem1∆ lineages rapidly increase in fitness and then slowly reach >90% of the fitness of their BEM1 ancestors at the end of the evolution. Sequencing their genomes and monitoring polarization reveals a common evolutionary trajectory, with a fixed sequence of adaptive mutations, each improving cell polarization by inactivating proteins. Our results show that organisms can be evolutionarily robust to physiologically destructive perturbations and suggest that recovery by gene inactivation can lead to rapid divergence in the parts list for cell biologically important functions. DOI:http://dx.doi.org/10.7554/eLife.09638.001 Cells use the genetic instructions provided by genes in particular combinations called ‘modules’ to perform particular jobs. Very different organisms can share many of the same modules because certain abilities are fundamental to the survival of all cells and so they have been retained over the course of evolution. That said, these modules may not necessarily involve the same genes because it is often possible to achieve the same result using different components. One way to study how those modules can diversify is to deliberately disrupt one of the genes in a module, and observe how the organism and its descendants respond over many generations. Other genes in these organisms may acquire genetic mutations that enable the genes to take on the role of the missing protein. However, the removal of a single component can be detrimental to the survival of the organisms or may affect many different processes. This can make it difficult to understand what is going on. A gene called BEM1 is crucial for yeast cells to establish polarity, that is, to allow the different sides of a cell to become distinct from one another. This activity is essential for the yeast to replicate itself. Previous studies have shown that the BEM1 gene had a different role in other species of fungi, which suggests that yeast may have other genes that previously assumed the role that BEM1 does now. In this study, Laan et al. removed BEM1 from yeast and allowed the population of mutant cells to evolve for a thousand generations. The approach differs from previous studies because Laan et al. deliberately selected for yeast that had acquired multiple genetic mutations that can together almost fully compensate for the loss of BEM1. Initially, the mutant cells grew very slowly, were abnormal in shape and likely to burst open. However, by the end of the experiment, the cells were able to grow almost as well as the original yeast cells had before the gene deletion. Genetic analysis revealed that the deletion of BEM1 triggers the inactivation of other genes that are also involved in the regulation of polarity, which largely restored the ability of the disrupted polarity module to work. This restoration follows a ‘reproducible trajectory’, as the same genes were switched off in the same order in different populations of yeast that were studied at the same time. The work is an example of reproducible evolution, whereby a specific order of changes to gene activity repeatedly enables cells with severe defects in important processes to adapt and restore a gene module, using whatever components they have left. The next challenge will be to understand how the particular roles of important modules affect their adaptability. DOI:http://dx.doi.org/10.7554/eLife.09638.002
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Affiliation(s)
- Liedewij Laan
- FAS Center for Systems Biology, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - John H Koschwanez
- FAS Center for Systems Biology, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - Andrew W Murray
- FAS Center for Systems Biology, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
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21
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Biswas A, Gauthier DT, Ranjan D, Zubair M. ISQuest: finding insertion sequences in prokaryotic sequence fragment data. Bioinformatics 2015; 31:3406-12. [PMID: 26116929 DOI: 10.1093/bioinformatics/btv388] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Accepted: 06/20/2015] [Indexed: 11/14/2022] Open
Abstract
MOTIVATION Insertion sequences (ISs) are transposable elements present in most bacterial and archaeal genomes that play an important role in genomic evolution. The increasing availability of sequenced prokaryotic genomes offers the opportunity to study ISs comprehensively, but development of efficient and accurate tools is required for discovery and annotation. Additionally, prokaryotic genomes are frequently deposited as incomplete, or draft stage because of the substantial cost and effort required to finish genome assembly projects. Development of methods to identify IS directly from raw sequence reads or draft genomes are therefore desirable. Software tools such as Optimized Annotation System for Insertion Sequences and IScan currently identify IS elements in completely assembled and annotated genomes; however, to our knowledge no methods have been developed to identify ISs from raw fragment data or partially assembled genomes. We have developed novel methods to solve this computationally challenging problem, and implemented these methods in the software package ISQuest. This software identifies bacterial ISs and their sequence elements-inverted and direct repeats-in raw read data or contigs using flexible search parameters. ISQuest is capable of finding ISs in hundreds of partially assembled genomes within hours, making it a valuable high-throughput tool for a global search of IS elements. We tested ISQuest on simulated read libraries of 3810 complete bacterial genomes and plasmids in GenBank and were capable of detecting 82% of the ISs and transposases annotated in GenBank with 80% sequence identity. CONTACT abiswas@cs.odu.edu.
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Affiliation(s)
| | - David T Gauthier
- Department of Biological Sciences, Old Dominion University, Norfolk, Virginia, USA
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22
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Carroll SM, Chubiz LM, Agashe D, Marx CJ. Parallel and Divergent Evolutionary Solutions for the Optimization of an Engineered Central Metabolism in Methylobacterium extorquens AM1. Microorganisms 2015; 3:152-74. [PMID: 27682084 PMCID: PMC5023240 DOI: 10.3390/microorganisms3020152] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 03/30/2015] [Accepted: 04/01/2015] [Indexed: 11/16/2022] Open
Abstract
Bioengineering holds great promise to provide fast and efficient biocatalysts for methanol-based biotechnology, but necessitates proven methods to optimize physiology in engineered strains. Here, we highlight experimental evolution as an effective means for optimizing an engineered Methylobacterium extorquens AM1. Replacement of the native formaldehyde oxidation pathway with a functional analog substantially decreased growth in an engineered Methylobacterium, but growth rapidly recovered after six hundred generations of evolution on methanol. We used whole-genome sequencing to identify the basis of adaptation in eight replicate evolved strains, and examined genomic changes in light of other growth and physiological data. We observed great variety in the numbers and types of mutations that occurred, including instances of parallel mutations at targets that may have been "rationalized" by the bioengineer, plus other "illogical" mutations that demonstrate the ability of evolution to expose unforeseen optimization solutions. Notably, we investigated mutations to RNA polymerase, which provided a massive growth benefit but are linked to highly aberrant transcriptional profiles. Overall, we highlight the power of experimental evolution to present genetic and physiological solutions for strain optimization, particularly in systems where the challenges of engineering are too many or too difficult to overcome via traditional engineering methods.
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Affiliation(s)
- Sean Michael Carroll
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
| | - Lon M Chubiz
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
- Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63103, USA.
| | - Deepa Agashe
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
- National Centre for Biological Sciences, Bangalore 560065, India.
| | - Christopher J Marx
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
- Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA.
- Department of Biological Sciences, Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID 83843, USA.
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Methenyl-Dephosphotetrahydromethanopterin Is a Regulatory Signal for Acclimation to Changes in Substrate Availability in Methylobacterium extorquens AM1. J Bacteriol 2015; 197:2020-6. [PMID: 25845846 DOI: 10.1128/jb.02595-14] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Accepted: 03/30/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED During an environmental perturbation, the survival of a cell and its response to the perturbation depend on both the robustness and functionality of the metabolic network. The regulatory mechanisms that allow the facultative methylotrophic bacterium Methylobacterium extorquens AM1 to effect the metabolic transition from succinate to methanol growth are not well understood. Methenyl-dephosphotetrahydromethanopterin (methenyl-dH4MPT), an early intermediate during methanol metabolism, transiently accumulated 7- to 11-fold after addition of methanol to a succinate-limited culture. This accumulation partially inhibited the activity of the methylene-H4MPT dehydrogenase, MtdA, restricting carbon flux to the assimilation cycles. A strain overexpressing the gene (mch) encoding the enzyme that consumes methenyl-dH4MPT did not accumulate methenyl-dH4MPT and had a growth rate that was 2.7-fold lower than that of the wild type. This growth defect demonstrates the physiological relevance of this enzymatic regulatory mechanism during the acclimation period. Changes in metabolites and enzymatic activities were analyzed in the strain overexpressing mch. Under these conditions, the activity of the enzyme coupling formaldehyde with dH4MPT (Fae) remained constant, with concomitant formaldehyde accumulation. Release of methenyl-dH4MPT regulation did not affect the induction of the serine cycle enzyme activities immediately after methanol addition, but after 1 h, the activity of these enzymes decreased, likely due to the toxicity of formaldehyde accumulation. Our results support the hypothesis that in a changing environment, the transient accumulation of methenyl-dH4MPT and inhibition of MtdA activity are strategies that permit flexibility and acclimation of the metabolic network while preventing the accumulation of the toxic compound formaldehyde. IMPORTANCE The identification and characterization of regulatory mechanisms for methylotrophy are in the early stages. We report a nontranscriptional regulatory mechanism that was found to operate as an immediate response for acclimation during changes in substrate availability. Methenyl-dH4MPT, an early intermediate during methanol oxidation, reversibly inhibits the methylene-H4MPT dehydrogenase, MtdA, when Methylobacterium extorquens is challenged to switch from succinate to methanol growth. Bypassing this regulatory mechanism causes formaldehyde to accumulate. Fae, the enzyme catalyzing the conversion of formaldehyde to methylene-dH4MPT, was also identified as another potential regulatory target using this strategy. The results herein further our understanding of the complex regulatory network in methylotrophy and will allow us to improve metabolic engineering strategies of methylotrophs for the production of value-added products.
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Nayak DD, Marx CJ. Experimental Horizontal Gene Transfer of Methylamine Dehydrogenase Mimics Prevalent Exchange in Nature and Overcomes the Methylamine Growth Constraints Posed by the Sub-Optimal N-Methylglutamate Pathway. Microorganisms 2015; 3:60-79. [PMID: 27682079 PMCID: PMC5023228 DOI: 10.3390/microorganisms3010060] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Revised: 02/16/2015] [Accepted: 02/16/2015] [Indexed: 12/14/2022] Open
Abstract
Methylamine plays an important role in the global carbon and nitrogen budget; microorganisms that grow on reduced single carbon compounds, methylotrophs, serve as a major biological sink for methylamine in aerobic environments. Two non-orthologous, functionally degenerate routes for methylamine oxidation have been studied in methylotrophic Proteobacteria: Methylamine dehydrogenase and the N-methylglutamate pathway. Recent work suggests the N-methylglutamate (NMG) pathway may be more common in nature than the well-studied methylamine dehydrogenase (MaDH, encoded by the mau gene cluster). However, the distribution of these pathways across methylotrophs has never been analyzed. Furthermore, even though horizontal gene transfer (HGT) is commonly invoked as a means to transfer these pathways between strains, the physiological barriers to doing so have not been investigated. We found that the NMG pathway is both more abundant and more universally distributed across methylotrophic Proteobacteria compared to MaDH, which displays a patchy distribution and has clearly been transmitted by HGT even amongst very closely related strains. This trend was especially prominent in well-characterized strains of the Methylobacterium extroquens species, which also display significant phenotypic variability during methylamine growth. Strains like Methylobacterium extorquens PA1 that only encode the NMG pathway grew on methylamine at least five-fold slower than strains like Methylobacterium extorquens AM1 that also possess the mau gene cluster. By mimicking a HGT event through the introduction of the M. extorquens AM1 mau gene cluster into the PA1 genome, the resulting strain instantaneously achieved a 4.5-fold increase in growth rate on methylamine and a 11-fold increase in fitness on methylamine, which even surpassed the fitness of M. extorquens AM1. In contrast, when three replicate populations of wild type M. extorquens PA1 were evolved on methylamine as the sole carbon and energy source for 150 generations neither fitness nor growth rate improved. These results suggest that the NMG pathway permits slow growth on methylamine and is widely distributed in methylotrophs; however, rapid growth on methylamine can be achieved quite readily through acquisition of the mau cluster by HGT.
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Affiliation(s)
- Dipti D Nayak
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
- Biological Sciences, University of Idaho, Moscow, ID 83844, USA.
| | - Christopher J Marx
- Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
- Biological Sciences, University of Idaho, Moscow, ID 83844, USA.
- Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA.
- Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID 83844, USA.
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Chou HH, Marx CJ, Sauer U. Transhydrogenase promotes the robustness and evolvability of E. coli deficient in NADPH production. PLoS Genet 2015; 11:e1005007. [PMID: 25715029 PMCID: PMC4340650 DOI: 10.1371/journal.pgen.1005007] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Accepted: 01/14/2015] [Indexed: 11/18/2022] Open
Abstract
Metabolic networks revolve around few metabolites recognized by diverse enzymes and involved in myriad reactions. Though hub metabolites are considered as stepping stones to facilitate the evolutionary expansion of biochemical pathways, changes in their production or consumption often impair cellular physiology through their system-wide connections. How does metabolism endure perturbations brought immediately by pathway modification and restore hub homeostasis in the long run? To address this question we studied laboratory evolution of pathway-engineered Escherichia coli that underproduces the redox cofactor NADPH on glucose. Literature suggests multiple possibilities to restore NADPH homeostasis. Surprisingly, genetic dissection of isolates from our twelve evolved populations revealed merely two solutions: (1) modulating the expression of membrane-bound transhydrogenase (mTH) in every population; (2) simultaneously consuming glucose with acetate, an unfavored byproduct normally excreted during glucose catabolism, in two subpopulations. Notably, mTH displays broad phylogenetic distribution and has also played a predominant role in laboratory evolution of Methylobacterium extorquens deficient in NADPH production. Convergent evolution of two phylogenetically and metabolically distinct species suggests mTH as a conserved buffering mechanism that promotes the robustness and evolvability of metabolism. Moreover, adaptive diversification via evolving dual substrate consumption highlights the flexibility of physiological systems to exploit ecological opportunities.
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Affiliation(s)
- Hsin-Hung Chou
- Institute of Molecular Systems Biology, ETH Zürich, Zürich, Switzerland
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
- * E-mail:
| | - Christopher J. Marx
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - Uwe Sauer
- Institute of Molecular Systems Biology, ETH Zürich, Zürich, Switzerland
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Ochsner AM, Sonntag F, Buchhaupt M, Schrader J, Vorholt JA. Methylobacterium extorquens: methylotrophy and biotechnological applications. Appl Microbiol Biotechnol 2014; 99:517-34. [PMID: 25432674 DOI: 10.1007/s00253-014-6240-3] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Revised: 11/14/2014] [Accepted: 11/16/2014] [Indexed: 01/06/2023]
Abstract
Methylotrophy is the ability to use reduced one-carbon compounds, such as methanol, as a single source of carbon and energy. Methanol is, due to its availability and potential for production from renewable resources, a valuable feedstock for biotechnology. Nature offers a variety of methylotrophic microorganisms that differ in their metabolism and represent resources for engineering of value-added products from methanol. The most extensively studied methylotroph is the Alphaproteobacterium Methylobacterium extorquens. Over the past five decades, the metabolism of M. extorquens has been investigated physiologically, biochemically, and more recently, using complementary omics technologies such as transcriptomics, proteomics, metabolomics, and fluxomics. These approaches, together with a genome-scale metabolic model, facilitate system-wide studies and the development of rational strategies for the successful generation of desired products from methanol. This review summarizes the knowledge of methylotrophy in M. extorquens, as well as the available tools and biotechnological applications.
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Affiliation(s)
- Andrea M Ochsner
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 4, 8093, Zurich, Switzerland
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Nayak DD, Marx CJ. Genetic and phenotypic comparison of facultative methylotrophy between Methylobacterium extorquens strains PA1 and AM1. PLoS One 2014; 9:e107887. [PMID: 25232997 PMCID: PMC4169470 DOI: 10.1371/journal.pone.0107887] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Accepted: 08/19/2014] [Indexed: 02/01/2023] Open
Abstract
Methylobacterium extorquens AM1, a strain serendipitously isolated half a century ago, has become the best-characterized model system for the study of aerobic methylotrophy (the ability to grow on reduced single-carbon compounds). However, with 5 replicons and 174 insertion sequence (IS) elements in the genome as well as a long history of domestication in the laboratory, genetic and genomic analysis of M. extorquens AM1 face several challenges. On the contrary, a recently isolated strain - M. extorquens PA1- is closely related to M. extorquens AM1 (100% 16S rRNA identity) and contains a streamlined genome with a single replicon and only 20 IS elements. With the exception of the methylamine dehydrogenase encoding gene cluster (mau), genes known to be involved in methylotrophy are well conserved between M. extorquens AM1 and M. extorquens PA1. In this paper we report four primary findings regarding methylotrophy in PA1. First, with a few notable exceptions, the repertoire of methylotrophy genes between PA1 and AM1 is extremely similar. Second, PA1 grows faster with higher yields compared to AM1 on C1 and multi-C substrates in minimal media, but AM1 grows faster in rich medium. Third, deletion mutants in PA1 throughout methylotrophy modules have the same C1 growth phenotypes observed in AM1. Finally, the precision of our growth assays revealed several unexpected growth phenotypes for various knockout mutants that serve as leads for future work in understanding their basis and generality across Methylobacterium strains.
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Affiliation(s)
- Dipti D. Nayak
- Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
| | - Christopher J. Marx
- Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
- Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, Massachusetts, United States of America
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
- Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, Idaho, United States of America
- * E-mail:
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The dynamics of diverse segmental amplifications in populations of Saccharomyces cerevisiae adapting to strong selection. G3-GENES GENOMES GENETICS 2014; 4:399-409. [PMID: 24368781 PMCID: PMC3962480 DOI: 10.1534/g3.113.009365] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Population adaptation to strong selection can occur through the sequential or parallel accumulation of competing beneficial mutations. The dynamics, diversity, and rate of fixation of beneficial mutations within and between populations are still poorly understood. To study how the mutational landscape varies across populations during adaptation, we performed experimental evolution on seven parallel populations of Saccharomyces cerevisiae continuously cultured in limiting sulfate medium. By combining quantitative polymerase chain reaction, array comparative genomic hybridization, restriction digestion and contour-clamped homogeneous electric field gel electrophoresis, and whole-genome sequencing, we followed the trajectory of evolution to determine the identity and fate of beneficial mutations. During a period of 200 generations, the yeast populations displayed parallel evolutionary dynamics that were driven by the coexistence of independent beneficial mutations. Selective amplifications rapidly evolved under this selection pressure, in particular common inverted amplifications containing the sulfate transporter gene SUL1. Compared with single clones, detailed analysis of the populations uncovers a greater complexity whereby multiple subpopulations arise and compete despite a strong selection. The most common evolutionary adaptation to strong selection in these populations grown in sulfate limitation is determined by clonal interference, with adaptive variants both persisting and replacing one another.
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Mapping the fitness landscape of gene expression uncovers the cause of antagonism and sign epistasis between adaptive mutations. PLoS Genet 2014; 10:e1004149. [PMID: 24586190 PMCID: PMC3937219 DOI: 10.1371/journal.pgen.1004149] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Accepted: 12/16/2013] [Indexed: 11/19/2022] Open
Abstract
How do adapting populations navigate the tensions between the costs of gene expression and the benefits of gene products to optimize the levels of many genes at once? Here we combined independently-arising beneficial mutations that altered enzyme levels in the central metabolism of Methylobacterium extorquens to uncover the fitness landscape defined by gene expression levels. We found strong antagonism and sign epistasis between these beneficial mutations. Mutations with the largest individual benefit interacted the most antagonistically with other mutations, a trend we also uncovered through analyses of datasets from other model systems. However, these beneficial mutations interacted multiplicatively (i.e., no epistasis) at the level of enzyme expression. By generating a model that predicts fitness from enzyme levels we could explain the observed sign epistasis as a result of overshooting the optimum defined by a balance between enzyme catalysis benefits and fitness costs. Knowledge of the phenotypic landscape also illuminated that, although the fitness peak was phenotypically far from the ancestral state, it was not genetically distant. Single beneficial mutations jumped straight toward the global optimum rather than being constrained to change the expression phenotypes in the correlated fashion expected by the genetic architecture. Given that adaptation in nature often results from optimizing gene expression, these conclusions can be widely applicable to other organisms and selective conditions. Poor interactions between individually beneficial alleles affecting gene expression may thus compromise the benefit of sex during adaptation and promote genetic differentiation. The pace and outcome of a series of adaptive steps in an evolving lineage depends upon how well different beneficial mutations stack on top of each other. We found that independent beneficial mutations that affected gene expression for a metabolic pathway did not work well together, and were often jointly deleterious. The most beneficial mutations interacted the most poorly with others, which was a trend we found common in other biological systems. Through generating a model that accounted for enzymatic benefits and expression costs, we uncovered that this antagonism was caused by a phenotype to fitness mapping that had an intermediate peak. This allowed us to predict the fitness effect of double mutants and to uncover that the single winning mutations tended to move straight to the peak in a single step. These findings demonstrate the importance of considering the phenotypic changes that cause nonlinear interactions between mutations upon fitness, and thus influence how populations evolve.
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Biosynthesis of polyhydroxyalkanoate copolymers from methanol by Methylobacterium extorquens AM1 and the engineered strains under cobalt-deficient conditions. Appl Microbiol Biotechnol 2014; 98:3715-25. [DOI: 10.1007/s00253-013-5490-9] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 12/20/2013] [Indexed: 10/25/2022]
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Carroll SM, Xue KS, Marx CJ. Laboratory divergence of Methylobacterium extorquens AM1 through unintended domestication and past selection for antibiotic resistance. BMC Microbiol 2014; 14:2. [PMID: 24384040 PMCID: PMC3926354 DOI: 10.1186/1471-2180-14-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 12/16/2013] [Indexed: 01/25/2023] Open
Abstract
Background A common assumption of microorganisms is that laboratory stocks will remain genetically and phenotypically constant over time, and across laboratories. It is becoming increasingly clear, however, that mutations can ruin strain integrity and drive the divergence or “domestication” of stocks. Since its discovery in 1960, a stock of Methylobacterium extorquens AM1 (“AM1”) has remained in the lab, propagated across numerous growth and storage conditions, researchers, and facilities. To explore the extent to which this lineage has diverged, we compared our own “Modern” stock of AM1 to a sample archived at a culture stock center shortly after the strain’s discovery. Stored as a lyophilized sample, we hypothesized that this Archival strain would better reflect the first-ever isolate of AM1 and reveal ways in which our Modern stock has changed through laboratory domestication or other means. Results Using whole-genome re-sequencing, we identified some 29 mutations – including single nucleotide polymorphisms, small indels, the insertion of mobile elements, and the loss of roughly 36 kb of DNA - that arose in the laboratory-maintained Modern lineage. Contrary to our expectations, Modern was both slower and less fit than Archival across a variety of growth substrates, and showed no improvement during long-term growth and storage. Modern did, however, outperform Archival during growth on nutrient broth, and in resistance to rifamycin, which was selected for by researchers in the 1980s. Recapitulating selection for rifamycin resistance in replicate Archival populations showed that mutations to RNA polymerase B (rpoB) substantially decrease growth in the absence of antibiotic, offering an explanation for slower growth in Modern stocks. Given the large number of genomic changes arising from domestication (28), it is somewhat surprising that the single other mutation attributed to purposeful laboratory selection accounts for much of the phenotypic divergence between strains. Conclusions These results highlight the surprising degree to which AM1 has diverged through a combination of unintended laboratory domestication and purposeful selection for rifamycin resistance. Instances of strain divergence are important, not only to ensure consistency of experimental results, but also to explore how microbes in the lab diverge from one another and from their wild counterparts.
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Affiliation(s)
| | | | - Christopher J Marx
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
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Spor A, Kvitek DJ, Nidelet T, Martin J, Legrand J, Dillmann C, Bourgais A, de Vienne D, Sherlock G, Sicard D. Phenotypic and genotypic convergences are influenced by historical contingency and environment in yeast. Evolution 2013; 68:772-790. [PMID: 24164389 DOI: 10.1111/evo.12302] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 10/14/2013] [Indexed: 12/26/2022]
Abstract
Different organisms have independently and recurrently evolved similar phenotypic traits at different points throughout history. This phenotypic convergence may be caused by genotypic convergence and in addition, constrained by historical contingency. To investigate how convergence may be driven by selection in a particular environment and constrained by history, we analyzed nine life-history traits and four metabolic traits during an experimental evolution of six yeast strains in four different environments. In each of the environments, the population converged toward a different multivariate phenotype. However, the evolution of most traits, including fitness components, was constrained by history. Phenotypic convergence was partly associated with the selection of mutations in genes involved in the same pathway. By further investigating the convergence in one gene, BMH1, mutated in 20% of the evolved populations, we show that both the history and the environment influenced the types of mutations (missense/nonsense), their location within the gene itself, as well as their effects on multiple traits. However, these effects could not be easily predicted from ancestors' phylogeny or past selection. Combined, our data highlight the role of pleiotropy and epistasis in shaping a rugged fitness landscape.
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Affiliation(s)
- Aymé Spor
- Univ Paris-Sud, UMR de Génétique Végétale, INRA / Univ Paris-Sud / CNRS, Ferme du Moulon, Gif-sur-Yvette, F-91190, France
| | - Daniel J Kvitek
- Department of Genetics, Stanford University, Stanford, CA 94305-5120, USA
| | | | - Juliette Martin
- Université Lyon 1; CNRS, UMR 5086; Bases Moléculaires et Structurales des Systèmes Infectieux, IBCP, 7 passage du, Vercors F-69367, France
| | - Judith Legrand
- Univ Paris-Sud, UMR de Génétique Végétale, INRA / Univ Paris-Sud / CNRS, Ferme du Moulon, Gif-sur-Yvette, F-91190, France
| | - Christine Dillmann
- Univ Paris-Sud, UMR de Génétique Végétale, INRA / Univ Paris-Sud / CNRS, Ferme du Moulon, Gif-sur-Yvette, F-91190, France
| | - Aurélie Bourgais
- CNRS, UMR de Génétique Végétale, INRA / Univ Paris-Sud / CNRS, Ferme du Moulon, Gif-sur-Yvette, F-91190, France
| | - Dominique de Vienne
- Univ Paris-Sud, UMR de Génétique Végétale, INRA / Univ Paris-Sud / CNRS, Ferme du Moulon, Gif-sur-Yvette, F-91190, France
| | - Gavin Sherlock
- Department of Genetics, Stanford University, Stanford, CA 94305-5120, USA
| | - Delphine Sicard
- Univ Paris-Sud, UMR de Génétique Végétale, INRA / Univ Paris-Sud / CNRS, Ferme du Moulon, Gif-sur-Yvette, F-91190, France
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Carroll SM, Lee MC, Marx CJ. SIGN EPISTASIS LIMITS EVOLUTIONARY TRADE-OFFS AT THE CONFLUENCE OF SINGLE- AND MULTI-CARBON METABOLISM INMETHYLOBACTERIUM EXTORQUENSAM1. Evolution 2013; 68:760-71. [DOI: 10.1111/evo.12301] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 10/02/2013] [Indexed: 01/09/2023]
Affiliation(s)
- Sean Michael Carroll
- Department of Organismic and Evolutionary Biology; Harvard University; Cambridge Massachusetts
| | - Ming-Chun Lee
- Department of Organismic and Evolutionary Biology; Harvard University; Cambridge Massachusetts
- Department of Biochemistry; University of Hong Kong; Pok Fu Lam Hong Kong
| | - Christopher J. Marx
- Department of Organismic and Evolutionary Biology; Harvard University; Cambridge Massachusetts
- Faculty of Arts and Sciences Center for Systems Biology; Harvard University; Cambridge Massachusetts
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Gao R, Stock AM. Evolutionary tuning of protein expression levels of a positively autoregulated two-component system. PLoS Genet 2013; 9:e1003927. [PMID: 24204322 PMCID: PMC3812086 DOI: 10.1371/journal.pgen.1003927] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Accepted: 09/13/2013] [Indexed: 11/18/2022] Open
Abstract
Cellular adaptation relies on the development of proper regulatory schemes for accurate control of gene expression levels in response to environmental cues. Over- or under-expression can lead to diminished cell fitness due to increased costs or insufficient benefits. Positive autoregulation is a common regulatory scheme that controls protein expression levels and gives rise to essential features in diverse signaling systems, yet its roles in cell fitness are less understood. It remains largely unknown how much protein expression is 'appropriate' for optimal cell fitness under specific extracellular conditions and how the dynamic environment shapes the regulatory scheme to reach appropriate expression levels. Here, we investigate the correlation of cell fitness and output response with protein expression levels of the E. coli PhoB/PhoR two-component system (TCS). In response to phosphate (Pi)-depletion, the PhoB/PhoR system activates genes involved in phosphorus assimilation as well as genes encoding themselves, similarly to many other positively autoregulated TCSs. We developed a bacteria competition assay in continuous cultures and discovered that different Pi conditions have conflicting requirements of protein expression levels for optimal cell fitness. Pi-replete conditions favored cells with low levels of PhoB/PhoR while Pi-deplete conditions selected for cells with high levels of PhoB/PhoR. These two levels matched PhoB/PhoR concentrations achieved via positive autoregulation in wild-type cells under Pi-replete and -deplete conditions, respectively. The fitness optimum correlates with the wild-type expression level, above which the phosphorylation output saturates, thus further increase in expression presumably provides no additional benefits. Laboratory evolution experiments further indicate that cells with non-ideal protein levels can evolve toward the optimal levels with diverse mutational strategies. Our results suggest that the natural protein expression levels and feedback regulatory schemes of TCSs are evolved to match the phosphorylation output of the system, which is determined by intrinsic activities of TCS proteins.
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Affiliation(s)
- Rong Gao
- Center for Advanced Biotechnology and Medicine, Department of Biochemistry and Molecular Biology, Rutgers University - Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
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van Ditmarsch D, Boyle KE, Sakhtah H, Oyler JE, Nadell CD, Déziel É, Dietrich LEP, Xavier JB. Convergent evolution of hyperswarming leads to impaired biofilm formation in pathogenic bacteria. Cell Rep 2013; 4:697-708. [PMID: 23954787 DOI: 10.1016/j.celrep.2013.07.026] [Citation(s) in RCA: 111] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Revised: 07/01/2013] [Accepted: 07/24/2013] [Indexed: 12/16/2022] Open
Abstract
Most bacteria in nature live in surface-associated communities rather than planktonic populations. Nonetheless, how surface-associated environments shape bacterial evolutionary adaptation remains poorly understood. Here, we show that subjecting Pseudomonas aeruginosa to repeated rounds of swarming, a collective form of surface migration, drives remarkable parallel evolution toward a hyperswarmer phenotype. In all independently evolved hyperswarmers, the reproducible hyperswarming phenotype is caused by parallel point mutations in a flagellar synthesis regulator, FleN, which locks the naturally monoflagellated bacteria in a multiflagellated state and confers a growth rate-independent advantage in swarming. Although hyperswarmers outcompete the ancestral strain in swarming competitions, they are strongly outcompeted in biofilm formation, which is an essential trait for P. aeruginosa in environmental and clinical settings. The finding that evolution in swarming colonies reliably produces evolution of poor biofilm formers supports the existence of an evolutionary trade-off between motility and biofilm formation.
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Affiliation(s)
- Dave van Ditmarsch
- Program in Computational Biology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA
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Exploring the costs of horizontal gene transfer. Trends Ecol Evol 2013; 28:489-95. [DOI: 10.1016/j.tree.2013.04.002] [Citation(s) in RCA: 261] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 04/15/2013] [Accepted: 04/25/2013] [Indexed: 11/20/2022]
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Chubiz LM, Purswani J, Carroll SM, Marx CJ. A novel pair of inducible expression vectors for use in Methylobacterium extorquens. BMC Res Notes 2013; 6:183. [PMID: 23648175 PMCID: PMC3694467 DOI: 10.1186/1756-0500-6-183] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Accepted: 03/27/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Due to the ever increasing use of diverse microbial taxa in basic research and industrial settings, there is a growing need for genetic tools to alter the physiology of these organisms. In particular, there is a dearth of inducible expression systems available for bacteria outside commonly used γ-proteobacteria, such as Escherichia coli or Pseudomonas species. To this end, we have sought to develop a pair of inducible expression vectors for use in the α-proteobacterium Methylobacterium extorquens, a model methylotroph. FINDINGS We found that the P(R) promoter from rhizobial phage 16-3 was active in M. extorquens and engineered the promoter to be inducible by either p-isopropyl benzoate (cumate) or anhydrotetracycline. These hybrid promoters, P(R/cmtO) and P(R/tetO), were found to have high levels of expression in M. extorquens with a regulatory range of 10-fold and 30-fold, respectively. Compared to an existing cumate-inducible (10-fold range), high-level expression system for M. extorquens, P(R/cmtO) and P(R/tetO) have 33% of the maximal activity but were able to repress gene expression 3 and 8-fold greater, respectively. Both promoters were observed to exhibit homogeneous, titratable activation dynamics rather than on-off, switch-like behavior. The utility of these promoters was further demonstrated by complementing loss of function of ftfL--essential for growth on methanol--where we show P(R/tetO) is capable of not only fully complementing function but also producing a conditional null phenotype. These promoters have been incorporated into a broad-host-range backbone allowing for potential use in a variety of bacterial hosts. CONCLUSIONS We have developed two novel expression systems for use in M. extorquens. The expression range of these vectors should allow for increased ability to explore cellular physiology in M. extorquens. Further, the P(R/tetO) promoter is capable of producing conditional null phenotypes, previously unattainable in M. extorquens. As both expression systems rely on the use of membrane permeable inducers, we suspect these expression vectors will be useful for ectopic gene expression in numerous proteobacteria.
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Affiliation(s)
- Lon M Chubiz
- Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA.
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Development of an optimized medium, strain and high-throughput culturing methods for Methylobacterium extorquens. PLoS One 2013; 8:e62957. [PMID: 23646164 PMCID: PMC3639900 DOI: 10.1371/journal.pone.0062957] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 03/26/2013] [Indexed: 11/19/2022] Open
Abstract
Methylobacterium extorquens strains are the best-studied methylotrophic model system, and their metabolism of single carbon compounds has been studied for over 50 years. Here we develop a new system for high-throughput batch culture of M. extorquens in microtiter plates by jointly optimizing the properties of the organism, the growth media and the culturing system. After removing cellulose synthase genes in M. extorquens strains AM1 and PA1 to prevent biofilm formation, we found that currently available lab automation equipment, integrated and managed by open source software, makes possible reliable estimates of the exponential growth rate. Using this system, we developed an optimized growth medium for M. extorquens using response surface methodologies. We found that media that used EDTA as a metal chelator inhibited growth and led to inconsistent culture conditions. In contrast, the new medium we developed with a PIPES buffer and metals chelated by citrate allowed for fast and more consistent growth rates. This new MethylobacteriumPIPES (‘MP’) medium was also robust to large deviations in its component ingredients which avoided batch effects from experiments that used media prepared at different times. MP medium allows for faster and more consistent growth than other media used for M. extorquens.
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Carroll SM, Marx CJ. Evolution after introduction of a novel metabolic pathway consistently leads to restoration of wild-type physiology. PLoS Genet 2013; 9:e1003427. [PMID: 23593025 PMCID: PMC3616920 DOI: 10.1371/journal.pgen.1003427] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2012] [Accepted: 02/11/2013] [Indexed: 01/22/2023] Open
Abstract
Organisms cope with physiological stressors through acclimatizing mechanisms in the short-term and adaptive mechanisms over evolutionary timescales. During adaptation to an environmental or genetic perturbation, beneficial mutations can generate numerous physiological changes: some will be novel with respect to prior physiological states, while others might either restore acclimatizing responses to a wild-type state, reinforce them further, or leave them unchanged. We examined the interplay of acclimatizing and adaptive responses at the level of global gene expression in Methylobacterium extorquens AM1 engineered with a novel central metabolism. Replacing central metabolism with a distinct, foreign pathway resulted in much slower growth than wild-type. After 600 generations of adaptation, however, eight replicate populations founded from this engineered ancestor had improved up to 2.5-fold. A comparison of global gene expression in wild-type, engineered, and all eight evolved strains revealed that the vast majority of changes during physiological adaptation effectively restored acclimatizing processes to wild-type expression states. On average, 93% of expression perturbations from the engineered strain were restored, with 70% of these occurring in perfect parallel across all eight replicate populations. Novel changes were common but typically restricted to one or a few lineages, and reinforcing changes were quite rare. Despite this, cases in which expression was novel or reinforced in parallel were enriched for loci harboring beneficial mutations. One case of parallel, reinforced changes was the pntAB transhydrogenase that uses NADH to reduce NADP+ to NADPH. We show that PntAB activity was highly correlated with the restoration of NAD(H) and NADP(H) pools perturbed in the engineered strain to wild-type levels, and with improved growth. These results suggest that much of the evolved response to genetic perturbation was a consequence rather than a cause of adaptation and that physiology avoided “reinventing the wheel” by restoring acclimatizing processes to the pre-stressed state. Acclimatizing and adaptive (evolutionary) processes allow organisms to thrive despite cellular and environmental perturbations. Our work examined whether adaptation restores stress responses towards wild-type (pre-stressed) versus novel physiological states during adaptation by studying a bacterium (Methylobacterium extorquens AM1) that was experimentally engineered and evolved with a novel central metabolism. The engineered strain was much slower and less fit than wild-type, but eight replicate populations evolved for six hundred generations showed substantial improvements. We found that changes in gene expression during adaptation consistently restored acclimatizing processes to the wild-type state, often in 8/8 evolved lines. Novel changes were common and largely restricted to one lineage; however, highly parallel novel changes revealed loci harboring beneficial mutations. Even rarer were reinforced changes, such as pntAB transhydrogenase, which increased beyond immediate acclimation during evolution to restore NAD(P)(H) metabolism and improve growth. Overall, a few novel or reinforcing changes drove the mass-restoration of physiology back to wild-type.
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Affiliation(s)
- Sean Michael Carroll
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
| | - Christopher J. Marx
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
- Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, Massachusetts, United States of America
- * E-mail:
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Synchronous waves of failed soft sweeps in the laboratory: remarkably rampant clonal interference of alleles at a single locus. Genetics 2013; 193:943-52. [PMID: 23307898 DOI: 10.1534/genetics.112.148502] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has increasingly been recognized that adapting populations of microbes contain not one, but many lineages continually arising and competing at once. This process, termed "clonal interference," alters the rate and dynamics of adaptation and biases winning mutations toward those with the largest selective effect. Here we uncovered a dramatic example of clonal interference between multiple similar mutations occurring at the same locus within replicate populations of Methylobacterium extorquens AM1. Because these mutational events involved the transposition of an insertion sequence into a narrow window of a single gene, they were both readily detectable at low frequencies and could be distinguished due to differences in insertion sites. This allowed us to detect up to 17 beneficial alleles of this type coexisting in a single population. Despite conferring a large selective benefit, the majority of these alleles rose and then fell in frequency due to other lineages emerging that were more fit. By comparing allele-frequency dynamics to the trajectories of fitness gains by these populations, we estimated the fitness values of the genotypes that contained these mutations. Collectively across all populations, these alleles arose upon backgrounds with a wide range of fitness values. Within any single population, however, multiple alleles tended to rise and fall synchronously during a single wave of multiple genotypes with nearly identical fitness values. These results suggest that alleles of large benefit arose repeatedly in failed "soft sweeps" during narrow windows of adaptation due to the combined effects of epistasis and clonal interference.
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Agashe D, Martinez-Gomez NC, Drummond DA, Marx CJ. Good codons, bad transcript: large reductions in gene expression and fitness arising from synonymous mutations in a key enzyme. Mol Biol Evol 2012; 30:549-60. [PMID: 23223712 PMCID: PMC3563975 DOI: 10.1093/molbev/mss273] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Biased codon usage in protein-coding genes is pervasive, whereby amino acids are largely encoded by a specific subset of possible codons. Within individual genes, codon bias is stronger at evolutionarily conserved residues, favoring codons recognized by abundant tRNAs. Although this observation suggests an overall pattern of selection for translation speed and/or accuracy, other work indicates that transcript structure or binding motifs drive codon usage. However, our understanding of codon bias evolution is constrained by limited experimental data on the fitness effects of altering codons in functional genes. To bridge this gap, we generated synonymous variants of a key enzyme-coding gene in Methylobacterium extorquens. We found that mutant gene expression, enzyme production, enzyme activity, and fitness were all significantly lower than wild-type. Surprisingly, encoding the gene using only rare codons decreased fitness by 40%, whereas an allele coded entirely by frequent codons decreased fitness by more than 90%. Increasing gene expression restored mutant fitness to varying degrees, demonstrating that the fitness disadvantage of synonymous mutants arose from a lack of beneficial protein rather than costs of protein production. Protein production was negatively correlated with the frequency of motifs with high affinity for the anti-Shine-Dalgarno sequence, suggesting ribosome pausing as the dominant cause of low mutant fitness. Together, our data support the idea that, although a particular set of codons are favored on average across a genome, in an individual gene selection can either act for or against codons depending on their local context.
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Affiliation(s)
- Deepa Agashe
- Department of Organismic and Evolutionary Biology, Biological Laboratories, Harvard University, MA, USA.
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FREQ-Seq: a rapid, cost-effective, sequencing-based method to determine allele frequencies directly from mixed populations. PLoS One 2012; 7:e47959. [PMID: 23118913 PMCID: PMC3485326 DOI: 10.1371/journal.pone.0047959] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 09/17/2012] [Indexed: 01/07/2023] Open
Abstract
Understanding evolutionary dynamics within microbial populations requires the ability to accurately follow allele frequencies through time. Here we present a rapid, cost-effective method (FREQ-Seq) that leverages Illumina next-generation sequencing for localized, quantitative allele frequency detection. Analogous to RNA-Seq, FREQ-Seq relies upon counts from the >105 reads generated per locus per time-point to determine allele frequencies. Loci of interest are directly amplified from a mixed population via two rounds of PCR using inexpensive, user-designed oligonucleotides and a bar-coded bridging primer system that can be regenerated in-house. The resulting bar-coded PCR products contain the adapters needed for Illumina sequencing, eliminating further library preparation. We demonstrate the utility of FREQ-Seq by determining the order and dynamics of beneficial alleles that arose as a microbial population, founded with an engineered strain of Methylobacterium, evolved to grow on methanol. Quantifying allele frequencies with minimal bias down to 1% abundance allowed effective analysis of SNPs, small in-dels and insertions of transposable elements. Our data reveal large-scale clonal interference during the early stages of adaptation and illustrate the utility of FREQ-Seq as a cost-effective tool for tracking allele frequencies in populations.
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Robinson DG, Lee MC, Marx CJ. OASIS: an automated program for global investigation of bacterial and archaeal insertion sequences. Nucleic Acids Res 2012; 40:e174. [PMID: 22904081 PMCID: PMC3526298 DOI: 10.1093/nar/gks778] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Insertion sequences (ISs) are simple transposable elements present in most bacterial and archaeal genomes and play an important role in genomic evolution. The recent expansion of sequenced genomes offers the opportunity to study ISs comprehensively, but this requires efficient and accurate tools for IS annotation. We have developed an open-source program called OASIS, or Optimized Annotation System for Insertion Sequences, which automatically annotates ISs within sequenced genomes. OASIS annotations of 1737 bacterial and archaeal genomes offered an unprecedented opportunity to examine IS evolution. At a broad scale, we found that most IS families are quite widespread; however, they are not present randomly across taxa. This may indicate differential loss, barriers to exchange and/or insufficient time to equilibrate across clades. The number of ISs increases with genome length, but there is both tremendous variation and no increase in IS density for genomes >2 Mb. At the finer scale of recently diverged genomes, the proportion of shared IS content falls sharply, suggesting loss and/or emergence of barriers to successful cross-infection occurs rapidly. Surprisingly, even after controlling for 16S rRNA sequence divergence, the same ISs were more likely to be shared between genomes labeled as the same species rather than as different species.
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Affiliation(s)
- David G Robinson
- Department of Organismic and Evolutionary Biology and Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA
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Marx CJ. Recovering from a bad start: rapid adaptation and tradeoffs to growth below a threshold density. BMC Evol Biol 2012; 12:109. [PMID: 22762241 PMCID: PMC3495640 DOI: 10.1186/1471-2148-12-109] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 06/15/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Bacterial growth in well-mixed culture is often assumed to be an autonomous process only depending upon the external conditions under control of the investigator. However, increasingly there is awareness that interactions between cells in culture can lead to surprising phenomena such as density-dependence in the initiation of growth. RESULTS Here I report the unexpected discovery of a density threshold for growth of a strain of Methylobacterium extorquens AM1 used to inoculate eight replicate populations that were evolved in methanol. Six of these populations failed to grow to the expected full density during the first couple transfers. Remarkably, the final cell number of six populations crashed to levels 60- to 400-fold smaller than their cohorts. Five of these populations recovered to full density soon after, but one population remained an order of magnitude smaller for over one hundred generations. These variable dynamics appeared to be due to a density threshold for growth that was specific to both this particular ancestral strain and to growth on methanol. When tested at full density, this population had become less fit than its ancestor. Simply increasing the initial dilution 16-fold reversed this result, revealing that this population had more than a 3-fold advantage when tested at this lower density. As this population evolved and ultimately recovered to the same final density range as the other populations this low-density advantage waned. CONCLUSIONS These results demonstrate surprisingly strong tradeoffs during adaptation to growth at low absolute densities that manifest over just a 16-fold change in density. Capturing laboratory examples of transitions to and from growth at low density may help us understand the physiological and evolutionary forces that have led to the unusual properties of natural bacteria that have specialized to low-density environments such as the open ocean.
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Affiliation(s)
- Christopher J Marx
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
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