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Jorrin B, Haskett TL, Knights HE, Martyn A, Underwood TJ, Dolliver J, Ledermann R, Poole PS. Stable, fluorescent markers for tracking synthetic communities and assembly dynamics. MICROBIOME 2024; 12:81. [PMID: 38715147 PMCID: PMC11075435 DOI: 10.1186/s40168-024-01792-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Accepted: 03/09/2024] [Indexed: 05/12/2024]
Abstract
BACKGROUND After two decades of extensive microbiome research, the current forefront of scientific exploration involves moving beyond description and classification to uncovering the intricate mechanisms underlying the coalescence of microbial communities. Deciphering microbiome assembly has been technically challenging due to their vast microbial diversity but establishing a synthetic community (SynCom) serves as a key strategy in unravelling this process. Achieving absolute quantification is crucial for establishing causality in assembly dynamics. However, existing approaches are primarily designed to differentiate a specific group of microorganisms within a particular SynCom. RESULTS To address this issue, we have developed the differential fluorescent marking (DFM) strategy, employing three distinguishable fluorescent proteins in single and double combinations. Building on the mini-Tn7 transposon, DFM capitalises on enhanced stability and broad applicability across diverse Proteobacteria species. The various DFM constructions are built using the pTn7-SCOUT plasmid family, enabling modular assembly, and facilitating the interchangeability of expression and antibiotic cassettes in a single reaction. DFM has no detrimental effects on fitness or community assembly dynamics, and through the application of flow cytometry, we successfully differentiated, quantified, and tracked a diverse six-member SynCom under various complex conditions like root rhizosphere showing a different colonisation assembly dynamic between pea and barley roots. CONCLUSIONS DFM represents a powerful resource that eliminates dependence on sequencing and/or culturing, thereby opening new avenues for studying microbiome assembly. Video Abstract.
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Affiliation(s)
- Beatriz Jorrin
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK.
| | - Timothy L Haskett
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK
| | - Hayley E Knights
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK
| | - Anna Martyn
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK
| | - Thomas J Underwood
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK
| | - Jessica Dolliver
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK
| | - Raphael Ledermann
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK
| | - Philip S Poole
- Molecular Plant Sciences Section, Department of Biology, University of Oxford, Oxford, OX1 3RB, UK
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Kearsley JVS, Sather LM, Finan TM. Sinorhizobium (Ensifer) meliloti. Trends Microbiol 2024; 32:516-518. [PMID: 38575429 DOI: 10.1016/j.tim.2024.03.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2024] [Revised: 03/05/2024] [Accepted: 03/07/2024] [Indexed: 04/06/2024]
Affiliation(s)
| | - Leah M Sather
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Turlough M Finan
- Department of Biology, McMaster University, Hamilton, Ontario, Canada.
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3
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Sather LM, Zamani M, Muhammed Z, Kearsley JVS, Fisher GT, Jones KM, Finan TM. A broadly distributed predicted helicase/nuclease confers phage resistance via abortive infection. Cell Host Microbe 2023; 31:343-355.e5. [PMID: 36893733 DOI: 10.1016/j.chom.2023.01.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 11/16/2022] [Accepted: 01/11/2023] [Indexed: 03/11/2023]
Abstract
There is strong selection for the evolution of systems that protect bacterial populations from viral attack. We report a single phage defense protein, Hna, that provides protection against diverse phages in Sinorhizobium meliloti, a nitrogen-fixing alpha-proteobacterium. Homologs of Hna are distributed widely across bacterial lineages, and a homologous protein from Escherichia coli also confers phage defense. Hna contains superfamily II helicase motifs at its N terminus and a nuclease motif at its C terminus, with mutagenesis of these motifs inactivating viral defense. Hna variably impacts phage DNA replication but consistently triggers an abortive infection response in which infected cells carrying the system die but do not release phage progeny. A similar host cell response is triggered in cells containing Hna upon expression of a phage-encoded single-stranded DNA binding protein (SSB), independent of phage infection. Thus, we conclude that Hna limits phage spread by initiating abortive infection in response to a phage protein.
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Affiliation(s)
- Leah M Sather
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1, Canada
| | - Maryam Zamani
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1, Canada
| | - Zahed Muhammed
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1, Canada
| | - Jason V S Kearsley
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1, Canada
| | - Gabrielle T Fisher
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Kathryn M Jones
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Turlough M Finan
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1, Canada.
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4
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Wein T, Wang Y, Barz M, Stücker FT, Hammerschmidt K, Dagan T. Essential gene acquisition destabilizes plasmid inheritance. PLoS Genet 2021; 17:e1009656. [PMID: 34252089 PMCID: PMC8297927 DOI: 10.1371/journal.pgen.1009656] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 07/22/2021] [Accepted: 06/09/2021] [Indexed: 11/25/2022] Open
Abstract
Extra-chromosomal genetic elements are important drivers of evolutionary transformations and ecological adaptations in prokaryotes with their evolutionary success often depending on their ‘utility’ to the host. Examples are plasmids encoding antibiotic resistance genes, which are known to proliferate in the presence of antibiotics. Plasmids carrying an essential host function are recognized as permanent residents in their host. Essential plasmids have been reported in several taxa where they often encode essential metabolic functions; nonetheless, their evolution remains poorly understood. Here we show that essential genes are rarely encoded on plasmids; evolving essential plasmids in Escherichia coli we further find that acquisition of an essential chromosomal gene by a plasmid can lead to plasmid extinction. A comparative genomics analysis of Escherichia isolates reveals few plasmid-encoded essential genes, yet these are often integrated into plasmid-related functions; an example is the GroEL/GroES chaperonin. Experimental evolution of a chaperonin-encoding plasmid shows that the acquisition of an essential gene reduces plasmid fitness regardless of the stability of plasmid inheritance. Our results suggest that essential plasmid emergence leads to a dose effect caused by gene redundancy. The detrimental effect of essential gene acquisition on plasmid inheritance constitutes a barrier for plasmid-mediated lateral gene transfer and supplies a mechanistic understanding for the rarity of essential genes in extra-chromosomal genetic elements. Mobile genetic elements have been extensively studied due to their role as agents of genetic innovation and rapid adaptation in prokaryotes. Specifically, prokaryotic plasmids have been the focus of investigation in the context of bacterial survival under growth limiting conditions with the prime example of resistance to antibiotics and heavy metals. In contrast, plasmids that encode for functions that are essential to their host viability are rarely described. We investigate the evolution of plasmids that encode for genes previously identified as essential for bacterial life. Our analysis of Escherichia isolates reveals only few plasmid-encoded essential genes, which likely function in the plasmid rather than the host life cycle. Following the evolution of plasmids encoding an essential gene in Escherichia coli in real time, we further find that the acquisition of a chromosomal essential gene may lead to plasmid loss. Our study supplies data and a mechanistic understanding on the rarity of essential genes in mobile genetic elements. We conclude that prokaryotic plasmids are rarely essential for their bacterial host.
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Affiliation(s)
- Tanita Wein
- Institute of General Microbiology, Kiel University, Kiel, Germany
- * E-mail:
| | - Yiqing Wang
- Institute of General Microbiology, Kiel University, Kiel, Germany
| | - Myriam Barz
- Institute of General Microbiology, Kiel University, Kiel, Germany
| | - Fenna T. Stücker
- Institute of General Microbiology, Kiel University, Kiel, Germany
| | | | - Tal Dagan
- Institute of General Microbiology, Kiel University, Kiel, Germany
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5
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Minimal gene set from Sinorhizobium ( Ensifer) meliloti pSymA required for efficient symbiosis with Medicago. Proc Natl Acad Sci U S A 2021; 118:2018015118. [PMID: 33384333 DOI: 10.1073/pnas.2018015118] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Reduction of N2 gas to ammonia in legume root nodules is a key component of sustainable agricultural systems. Root nodules are the result of a symbiosis between leguminous plants and bacteria called rhizobia. Both symbiotic partners play active roles in establishing successful symbiosis and nitrogen fixation: while root nodule development is mostly controlled by the plant, the rhizobia induce nodule formation, invade, and perform N2 fixation once inside the plant cells. Many bacterial genes involved in the rhizobia-legume symbiosis are known, and there is much interest in engineering the symbiosis to include major nonlegume crops such as corn, wheat, and rice. We sought to identify and combine a minimal bacterial gene complement necessary and sufficient for symbiosis. We analyzed a model rhizobium, Sinorhizobium (Ensifer) meliloti, using a background strain in which the 1.35-Mb symbiotic megaplasmid pSymA was removed. Three regions representing 162 kb of pSymA were sufficient to recover a complete N2-fixing symbiosis with alfalfa, and a targeted assembly of this gene complement achieved high levels of symbiotic N2 fixation. The resulting gene set contained just 58 of 1,290 pSymA protein-coding genes. To generate a platform for future synthetic manipulation, the minimal symbiotic genes were reorganized into three discrete nod, nif, and fix modules. These constructs will facilitate directed studies toward expanding the symbiosis to other plant partners. They also enable forward-type approaches to identifying genetic components that may not be essential for symbiosis, but which modulate the rhizobium's competitiveness for nodulation and the effectiveness of particular rhizobia-plant symbioses.
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Morgado SM, Vicente ACP. Comprehensive in silico survey of the Mycolicibacterium mobilome reveals an as yet underexplored diversity. Microb Genom 2021; 7:mgen000533. [PMID: 33620305 PMCID: PMC8190616 DOI: 10.1099/mgen.0.000533] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Accepted: 01/28/2021] [Indexed: 11/30/2022] Open
Abstract
The mobilome plays a crucial role in bacterial adaptation and is therefore a starting point to understand and establish the gene flow occurring in the process of bacterial evolution. This is even more so if we consider that the mobilome of environmental bacteria can be the reservoir of genes that may later appear in the clinic. Recently, new genera have been proposed in the family Mycobacteriaceae, including the genus Mycolicibacterium, which encompasses dozens of species of agricultural, biotechnological, clinical and ecological importance, being ubiquitous in several environments. The current scenario in the Mycobacteriaceae mobilome has some bias because most of the characterized mycobacteriophages were isolated using a single host strain, and the few plasmids reported mainly relate to the genus Mycobacterium. To fill in the gaps in these issues, we performed a systematic in silico study of these mobile elements based on 242 available genomes of the genus Mycolicibacterium. The analyses identified 156 putative plasmids (19 conjugative, 45 mobilizable and 92 non-mobilizable) and 566 prophages in 86 and 229 genomes, respectively. Moreover, a contig was characterized by resembling an actinomycete integrative and conjugative element (AICE). Within this diversity of mobile genetic elements, there is a pool of genes associated with several canonical functions, in addition to adaptive traits, such as virulence and resistance to antibiotics and metals (mercury and arsenic). The type-VII secretion system was a common feature in the predicted plasmids, being associated with genes encoding virulent proteins (EsxA, EsxB, PE and PPE). In addition to the characterization of plasmids and prophages of the family Mycobacteriaceae, this study showed an abundance of these genetic elements in a dozen species of the genus Mycolicibacterium.
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7
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Yang LL, Jiang Z, Li Y, Wang ET, Zhi XY. Plasmids Related to the Symbiotic Nitrogen Fixation Are Not Only Cooperated Functionally but Also May Have Evolved over a Time Span in Family Rhizobiaceae. Genome Biol Evol 2020; 12:2002-2014. [PMID: 32687170 PMCID: PMC7719263 DOI: 10.1093/gbe/evaa152] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/15/2020] [Indexed: 12/17/2022] Open
Abstract
Rhizobia are soil bacteria capable of forming symbiotic nitrogen-fixing nodules associated with leguminous plants. In fast-growing legume-nodulating rhizobia, such as the species in the family Rhizobiaceae, the symbiotic plasmid is the main genetic basis for nitrogen-fixing symbiosis, and is susceptible to horizontal gene transfer. To further understand the symbioses evolution in Rhizobiaceae, we analyzed the pan-genome of this family based on 92 genomes of type/reference strains and reconstructed its phylogeny using a phylogenomics approach. Intriguingly, although the genetic expansion that occurred in chromosomal regions was the main reason for the high proportion of low-frequency flexible gene families in the pan-genome, gene gain events associated with accessory plasmids introduced more genes into the genomes of nitrogen-fixing species. For symbiotic plasmids, although horizontal gene transfer frequently occurred, transfer may be impeded by, such as, the host’s physical isolation and soil conditions, even among phylogenetically close species. During coevolution with leguminous hosts, the plasmid system, including accessory and symbiotic plasmids, may have evolved over a time span, and provided rhizobial species with the ability to adapt to various environmental conditions and helped them achieve nitrogen fixation. These findings provide new insights into the phylogeny of Rhizobiaceae and advance our understanding of the evolution of symbiotic nitrogen fixation.
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Affiliation(s)
- Ling-Ling Yang
- Yunnan Institute of Microbiology, School of Life Sciences, Yunnan University, Kunming, Yunnan, PR China
| | - Zhao Jiang
- Yunnan Institute of Microbiology, School of Life Sciences, Yunnan University, Kunming, Yunnan, PR China
| | - Yan Li
- Key Laboratory of Coastal Biology and Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, Shandong, PR China
| | - En-Tao Wang
- Departamento de Microbiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Mexico City D.F., México
| | - Xiao-Yang Zhi
- Yunnan Institute of Microbiology, School of Life Sciences, Yunnan University, Kunming, Yunnan, PR China
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8
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diCenzo GC, Mengoni A, Perrin E. Chromids Aid Genome Expansion and Functional Diversification in the Family Burkholderiaceae. Mol Biol Evol 2019; 36:562-574. [PMID: 30608550 DOI: 10.1093/molbev/msy248] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Multipartite genomes, containing at least two large replicons, are found in diverse bacteria; however, the advantage of this genome structure remains incompletely understood. Here, we perform comparative genomics of hundreds of finished β-proteobacterial genomes to gain insights into the role and emergence of multipartite genomes. Almost all essential secondary replicons (chromids) of the β-proteobacteria are found in the family Burkholderiaceae. These replicons arose from just two plasmid acquisition events, and they were likely stabilized early in their evolution by the presence of core genes. On average, Burkholderiaceae genera with multipartite genomes had a larger total genome size, but smaller chromosome, than genera without secondary replicons. Pangenome-level functional enrichment analyses suggested that interreplicon functional biases are partially driven by the enrichment of secondary replicons in the accessory pangenome fraction. Nevertheless, the small overlap in orthologous groups present in each replicon's pangenome indicated a clear functional separation of the replicons. Chromids appeared biased to environmental adaptation, as the functional categories enriched on chromids were also overrepresented on the chromosomes of the environmental genera (Paraburkholderia and Cupriavidus) compared with the pathogenic genera (Burkholderia and Ralstonia). Using ancestral state reconstruction, it was predicted that the rate of accumulation of modern-day genes by chromids was more rapid than the rate of gene accumulation by the chromosomes. Overall, the data are consistent with a model where the primary advantage of secondary replicons is in facilitating increased rates of gene acquisition through horizontal gene transfer, consequently resulting in replicons enriched in genes associated with adaptation to novel environments.
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Affiliation(s)
- George C diCenzo
- Department of Biology, University of Florence, Sesto Fiorentino, Florence, Italy
| | - Alessio Mengoni
- Department of Biology, University of Florence, Sesto Fiorentino, Florence, Italy
| | - Elena Perrin
- Department of Biology, University of Florence, Sesto Fiorentino, Florence, Italy
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Brumwell SL, MacLeod MR, Huang T, Cochrane RR, Meaney RS, Zamani M, Matysiakiewicz O, Dan KN, Janakirama P, Edgell DR, Charles TC, Finan TM, Karas BJ. Designer Sinorhizobium meliloti strains and multi-functional vectors enable direct inter-kingdom DNA transfer. PLoS One 2019; 14:e0206781. [PMID: 31206509 PMCID: PMC6576745 DOI: 10.1371/journal.pone.0206781] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Accepted: 05/31/2019] [Indexed: 12/18/2022] Open
Abstract
Storage, manipulation and delivery of DNA fragments is crucial for synthetic biology applications, subsequently allowing organisms of interest to be engineered with genes or pathways to produce desirable phenotypes such as disease or drought resistance in plants, or for synthesis of a specific chemical product. However, DNA with high G+C content can be unstable in many host organisms including Saccharomyces cerevisiae. Here, we report the development of Sinorhizobium meliloti, a nitrogen-fixing plant symbioticα-Proteobacterium, as a novel host that can store DNA, and mobilize DNA to E. coli, S. cerevisiae, and the eukaryotic microalgae Phaeodactylum tricornutum. To achieve this, we deleted the hsdR restriction-system in multiple reduced genome strains of S. meliloti that enable DNA transformation with up to 1.4 x 105 and 2.1 x 103 CFU μg-1 of DNA efficiency using electroporation and a newly developed polyethylene glycol transformation method, respectively. Multi-host and multi-functional shuttle vectors (MHS) were constructed and stably propagated in S. meliloti, E. coli, S. cerevisiae, and P. tricornutum. We also developed protocols and demonstrated direct transfer of these MHS vectors via conjugation from S. meliloti to E. coli, S. cerevisiae, and P. tricornutum. The development of S. meliloti as a new host for inter-kingdom DNA transfer will be invaluable for synthetic biology research and applications, including the installation and study of genes and biosynthetic pathways into organisms of interest in industry and agriculture.
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Affiliation(s)
- Stephanie L Brumwell
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | | | - Tony Huang
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | - Ryan R Cochrane
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | | | - Maryam Zamani
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | | | - Kaitlyn N Dan
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | | | - David R Edgell
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | - Trevor C Charles
- Department of Biology, University of Waterloo, Waterloo, ON, Canada
| | - Turlough M Finan
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Bogumil J Karas
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.,Designer Microbes Inc., London, ON, Canada
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10
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diCenzo GC, Zamani M, Checcucci A, Fondi M, Griffitts JS, Finan TM, Mengoni A. Multidisciplinary approaches for studying rhizobium–legume symbioses. Can J Microbiol 2019; 65:1-33. [DOI: 10.1139/cjm-2018-0377] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The rhizobium–legume symbiosis is a major source of fixed nitrogen (ammonia) in the biosphere. The potential for this process to increase agricultural yield while reducing the reliance on nitrogen-based fertilizers has generated interest in understanding and manipulating this process. For decades, rhizobium research has benefited from the use of leading techniques from a very broad set of fields, including population genetics, molecular genetics, genomics, and systems biology. In this review, we summarize many of the research strategies that have been employed in the study of rhizobia and the unique knowledge gained from these diverse tools, with a focus on genome- and systems-level approaches. We then describe ongoing synthetic biology approaches aimed at improving existing symbioses or engineering completely new symbiotic interactions. The review concludes with our perspective of the future directions and challenges of the field, with an emphasis on how the application of a multidisciplinary approach and the development of new methods will be necessary to ensure successful biotechnological manipulation of the symbiosis.
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Affiliation(s)
- George C. diCenzo
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Maryam Zamani
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Alice Checcucci
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Marco Fondi
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Joel S. Griffitts
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA
| | - Turlough M. Finan
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Alessio Mengoni
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
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11
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Fournes F, Val ME, Skovgaard O, Mazel D. Replicate Once Per Cell Cycle: Replication Control of Secondary Chromosomes. Front Microbiol 2018; 9:1833. [PMID: 30131796 PMCID: PMC6090056 DOI: 10.3389/fmicb.2018.01833] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Accepted: 07/23/2018] [Indexed: 12/13/2022] Open
Abstract
Faithful vertical transmission of genetic information, especially of essential core genes, is a prerequisite for bacterial survival. Hence, replication of all the replicons is tightly controlled to ensure that all daughter cells get the same genome copy as their mother cell. Essential core genes are very often carried by the main chromosome. However they can occasionally be found on secondary chromosomes, recently renamed chromids. Chromids have evolved from non-essential megaplasmids, and further acquired essential core genes and a genomic signature closed to that of the main chromosome. All chromids carry a plasmidic replication origin, belonging so far to either the iterons or repABC type. Based on these differences, two categories of chromids have been distinguished. In this review, we focus on the replication initiation controls of these two types of chromids. We show that the sophisticated mechanisms controlling their replication evolved from their plasmid counterparts to allow a timely controlled replication, occurring once per cell cycle.
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Affiliation(s)
- Florian Fournes
- Unité Plasticité du Génome Bactérien, Département Génomes et Génétique, Institut Pasteur, Paris, France.,UMR3525, Centre National de la Recherche Scientifique, Paris, France
| | - Marie-Eve Val
- Unité Plasticité du Génome Bactérien, Département Génomes et Génétique, Institut Pasteur, Paris, France.,UMR3525, Centre National de la Recherche Scientifique, Paris, France
| | - Ole Skovgaard
- Department of Science and Environment, Roskilde University, Roskilde, Denmark
| | - Didier Mazel
- Unité Plasticité du Génome Bactérien, Département Génomes et Génétique, Institut Pasteur, Paris, France.,UMR3525, Centre National de la Recherche Scientifique, Paris, France
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Inter-replicon Gene Flow Contributes to Transcriptional Integration in the Sinorhizobium meliloti Multipartite Genome. G3-GENES GENOMES GENETICS 2018; 8:1711-1720. [PMID: 29563186 PMCID: PMC5940162 DOI: 10.1534/g3.117.300405] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Integration of newly acquired genes into existing regulatory networks is necessary for successful horizontal gene transfer (HGT). Ten percent of bacterial species contain at least two DNA replicons over 300 kilobases in size, with the secondary replicons derived predominately through HGT. The Sinorhizobium meliloti genome is split between a 3.7 Mb chromosome, a 1.7 Mb chromid consisting largely of genes acquired through ancient HGT, and a 1.4 Mb megaplasmid consisting primarily of recently acquired genes. Here, RNA-sequencing is used to examine the transcriptional consequences of massive, synthetic genome reduction produced through the removal of the megaplasmid and/or the chromid. Removal of the pSymA megaplasmid influenced the transcription of only six genes. In contrast, removal of the chromid influenced expression of ∼8% of chromosomal genes and ∼4% of megaplasmid genes. This was mediated in part by the loss of the ETR DNA region whose presence on pSymB is due to a translocation from the chromosome. No obvious functional bias among the up-regulated genes was detected, although genes with putative homologs on the chromid were enriched. Down-regulated genes were enriched in motility and sensory transduction pathways. Four transcripts were examined further, and in each case the transcriptional change could be traced to loss of specific pSymB regions. In particularly, a chromosomal transporter was induced due to deletion of bdhA likely mediated through 3-hydroxybutyrate accumulation. These data provide new insights into the evolution of the multipartite bacterial genome, and more generally into the integration of horizontally acquired genes into the transcriptome.
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13
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Jiao J, Ni M, Zhang B, Zhang Z, Young JPW, Chan TF, Chen WX, Lam HM, Tian CF. Coordinated regulation of core and accessory genes in the multipartite genome of Sinorhizobium fredii. PLoS Genet 2018; 14:e1007428. [PMID: 29795552 PMCID: PMC5991415 DOI: 10.1371/journal.pgen.1007428] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Revised: 06/06/2018] [Accepted: 05/18/2018] [Indexed: 01/18/2023] Open
Abstract
Prokaryotes benefit from having accessory genes, but it is unclear how accessory genes can be linked with the core regulatory network when developing adaptations to new niches. Here we determined hierarchical core/accessory subsets in the multipartite pangenome (composed of genes from the chromosome, chromid and plasmids) of the soybean microsymbiont Sinorhizobium fredii by comparing twelve Sinorhizobium genomes. Transcriptomes of two S. fredii strains at mid-log and stationary growth phases and in symbiotic conditions were obtained. The average level of gene expression, variation of expression between different conditions, and gene connectivity within the co-expression network were positively correlated with the gene conservation level from strain-specific accessory genes to genus core. Condition-dependent transcriptomes exhibited adaptive transcriptional changes in pangenome subsets shared by the two strains, while strain-dependent transcriptomes were enriched with accessory genes on the chromid. Proportionally more chromid genes than plasmid genes were co-expressed with chromosomal genes, while plasmid genes had a higher within-replicon connectivity in expression than chromid ones. However, key nitrogen fixation genes on the symbiosis plasmid were characterized by high connectivity in both within- and between-replicon analyses. Among those genes with host-specific upregulation patterns, chromosomal znu and mdt operons, encoding a conserved high-affinity zinc transporter and an accessory multi-drug efflux system, respectively, were experimentally demonstrated to be involved in host-specific symbiotic adaptation. These findings highlight the importance of integrative regulation of hierarchical core/accessory components in the multipartite genome of bacteria during niche adaptation and in shaping the prokaryotic pangenome in the long run.
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Affiliation(s)
- Jian Jiao
- State Key Laboratory of Agrobiotechnology, and College of Biological Sciences, China Agricultural University, Beijing, China
- Rhizobium Research Center, China Agricultural University, Beijing, China
| | - Meng Ni
- School of Life Sciences and Center for Soybean Research of the Partner State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong SAR
| | - Biliang Zhang
- State Key Laboratory of Agrobiotechnology, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Ziding Zhang
- State Key Laboratory of Agrobiotechnology, and College of Biological Sciences, China Agricultural University, Beijing, China
| | | | - Ting-Fung Chan
- School of Life Sciences and Center for Soybean Research of the Partner State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong SAR
| | - Wen Xin Chen
- State Key Laboratory of Agrobiotechnology, and College of Biological Sciences, China Agricultural University, Beijing, China
- Rhizobium Research Center, China Agricultural University, Beijing, China
| | - Hon-Ming Lam
- School of Life Sciences and Center for Soybean Research of the Partner State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong SAR
| | - Chang Fu Tian
- State Key Laboratory of Agrobiotechnology, and College of Biological Sciences, China Agricultural University, Beijing, China
- Rhizobium Research Center, China Agricultural University, Beijing, China
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14
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Nelson M, Guhlin J, Epstein B, Tiffin P, Sadowsky MJ. The complete replicons of 16 Ensifer meliloti strains offer insights into intra- and inter-replicon gene transfer, transposon-associated loci, and repeat elements. Microb Genom 2018; 4. [PMID: 29671722 PMCID: PMC5994717 DOI: 10.1099/mgen.0.000174] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Ensifer meliloti (formerly Rhizobium meliloti and Sinorhizobium meliloti) is a model bacterium for understanding legume–rhizobial symbioses. The tripartite genome of E. meliloti consists of a chromosome, pSymA and pSymB, and in some instances strain-specific accessory plasmids. The majority of previous sequencing studies have relied on the use of assemblies generated from short read sequencing, which leads to gaps and assembly errors. Here we used PacBio-based, long-read assemblies and were able to assemble, de novo, complete circular replicons. In this study, we sequenced, de novo-assembled and analysed 10 E. meliloti strains. Sequence comparisons were also done with data from six previously published genomes. We identified genome differences between the replicons, including mol% G+C and gene content, nucleotide repeats, and transposon-associated loci. Additionally, genomic rearrangements both within and between replicons were identified, providing insight into evolutionary processes at the structural level. There were few cases of inter-replicon gene transfer of core genes between the main replicons. Accessory plasmids were more similar to pSymA than to either pSymB or the chromosome, with respect to gene content, transposon content and G+C content. In our population, the accessory plasmids appeared to share an open genome with pSymA, which contains many nodulation- and nitrogen fixation-related genes. This may explain previous observations that horizontal gene transfer has a greater effect on the content of pSymA than pSymB, or the chromosome, and why some rhizobia show unstable nodulation phenotypes on legume hosts.
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Affiliation(s)
- Matthew Nelson
- 1Biotechnology Institute and Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108, USA
| | - Joseph Guhlin
- 2Department of Plant and Microbial Biology, University of Minnesota, St. Paul, MN 55108, USA
| | - Brendan Epstein
- 2Department of Plant and Microbial Biology, University of Minnesota, St. Paul, MN 55108, USA
| | - Peter Tiffin
- 2Department of Plant and Microbial Biology, University of Minnesota, St. Paul, MN 55108, USA
| | - Michael J Sadowsky
- 1Biotechnology Institute and Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108, USA
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15
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diCenzo GC, Benedict AB, Fondi M, Walker GC, Finan TM, Mengoni A, Griffitts JS. Robustness encoded across essential and accessory replicons of the ecologically versatile bacterium Sinorhizobium meliloti. PLoS Genet 2018; 14:e1007357. [PMID: 29672509 PMCID: PMC5929573 DOI: 10.1371/journal.pgen.1007357] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Revised: 05/01/2018] [Accepted: 04/10/2018] [Indexed: 11/19/2022] Open
Abstract
Bacterial genome evolution is characterized by gains, losses, and rearrangements of functional genetic segments. The extent to which large-scale genomic alterations influence genotype-phenotype relationships has not been investigated in a high-throughput manner. In the symbiotic soil bacterium Sinorhizobium meliloti, the genome is composed of a chromosome and two large extrachromosomal replicons (pSymA and pSymB, which together constitute 45% of the genome). Massively parallel transposon insertion sequencing (Tn-seq) was employed to evaluate the contributions of chromosomal genes to growth fitness in both the presence and absence of these extrachromosomal replicons. Ten percent of chromosomal genes from diverse functional categories are shown to genetically interact with pSymA and pSymB. These results demonstrate the pervasive robustness provided by the extrachromosomal replicons, which is further supported by constraint-based metabolic modeling. A comprehensive picture of core S. meliloti metabolism was generated through a Tn-seq-guided in silico metabolic network reconstruction, producing a core network encompassing 726 genes. This integrated approach facilitated functional assignments for previously uncharacterized genes, while also revealing that Tn-seq alone missed over a quarter of wild-type metabolism. This work highlights the many functional dependencies and epistatic relationships that may arise between bacterial replicons and across a genome, while also demonstrating how Tn-seq and metabolic modeling can be used together to yield insights not obtainable by either method alone. S. meliloti, which has traditionally facilitated ground-breaking insights into symbiotic communication, is also emerging as an excellent model for studying the evolution of functional relationships between bacterial chromosomes and anciently acquired accessory replicons. Multi-replicon genome architecture is present in ~ 10% of presently sequenced bacterial genomes. The S. meliloti genome is composed of three circular replicons, two of which are dispensable even though they encompass nearly half of the protein-coding genes in this organism. The construction of strains lacking these replicons has enabled a straightforward, genome-wide analysis of interactions between the chromosome and the non-essential replicons, revealing extensive functional cooperation between these genomic components. This analysis enabled a substantial refinement of a metabolic network model for S. meliloti. The integration of massively parallel genotype-phenotype screening with in silico metabolic reconstruction has enhanced our understanding of metabolic network structure as it relates to genome evolution in S. meliloti, and exemplifies an approach that may be productively applied to other taxa. The combined experimental and computational approach employed here further provides unique insights into the pervasive genetic interactions that may exist within large bacterial genomes.
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Affiliation(s)
- George C. diCenzo
- Department of Biology, University of Florence, Sesto Fiorentino, FI, Italy
- * E-mail:
| | - Alex B. Benedict
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States of America
| | - Marco Fondi
- Department of Biology, University of Florence, Sesto Fiorentino, FI, Italy
| | - Graham C. Walker
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States of America
| | | | - Alessio Mengoni
- Department of Biology, University of Florence, Sesto Fiorentino, FI, Italy
| | - Joel S. Griffitts
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States of America
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16
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Abstract
Rhizobia are some of the best-studied plant microbiota. These oligotrophic Alphaproteobacteria or Betaproteobacteria form symbioses with their legume hosts. Rhizobia must exist in soil and compete with other members of the microbiota before infecting legumes and forming N2-fixing bacteroids. These dramatic lifestyle and developmental changes are underpinned by large genomes and even more complex pan-genomes, which encompass the whole population and are subject to rapid genetic exchange. The ability to respond to plant signals and chemoattractants and to colonize nutrient-rich roots are crucial for the competitive success of these bacteria. The availability of a large body of genomic, physiological, biochemical and ecological studies makes rhizobia unique models for investigating community interactions and plant colonization.
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17
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diCenzo GC, Finan TM. Techniques for Large-Scale Bacterial Genome Manipulation and Characterization of the Mutants with Respect to In Silico Metabolic Reconstructions. Methods Mol Biol 2018; 1716:291-314. [PMID: 29222759 DOI: 10.1007/978-1-4939-7528-0_13] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The rate at which all genes within a bacterial genome can be identified far exceeds the ability to characterize these genes. To assist in associating genes with cellular functions, a large-scale bacterial genome deletion approach can be employed to rapidly screen tens to thousands of genes for desired phenotypes. Here, we provide a detailed protocol for the generation of deletions of large segments of bacterial genomes that relies on the activity of a site-specific recombinase. In this procedure, two recombinase recognition target sequences are introduced into known positions of a bacterial genome through single cross-over plasmid integration. Subsequent expression of the site-specific recombinase mediates recombination between the two target sequences, resulting in the excision of the intervening region and its loss from the genome. We further illustrate how this deletion system can be readily adapted to function as a large-scale in vivo cloning procedure, in which the region excised from the genome is captured as a replicative plasmid. We next provide a procedure for the metabolic analysis of bacterial large-scale genome deletion mutants using the Biolog Phenotype MicroArray™ system. Finally, a pipeline is described, and a sample Matlab script is provided, for the integration of the obtained data with a draft metabolic reconstruction for the refinement of the reactions and gene-protein-reaction relationships in a metabolic reconstruction.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Turlough M Finan
- Department of Biology, McMaster University, Hamilton, ON, Canada.
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18
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diCenzo GC, Finan TM. The Divided Bacterial Genome: Structure, Function, and Evolution. Microbiol Mol Biol Rev 2017; 81:e00019-17. [PMID: 28794225 PMCID: PMC5584315 DOI: 10.1128/mmbr.00019-17] [Citation(s) in RCA: 135] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Approximately 10% of bacterial genomes are split between two or more large DNA fragments, a genome architecture referred to as a multipartite genome. This multipartite organization is found in many important organisms, including plant symbionts, such as the nitrogen-fixing rhizobia, and plant, animal, and human pathogens, including the genera Brucella, Vibrio, and Burkholderia. The availability of many complete bacterial genome sequences means that we can now examine on a broad scale the characteristics of the different types of DNA molecules in a genome. Recent work has begun to shed light on the unique properties of each class of replicon, the unique functional role of chromosomal and nonchromosomal DNA molecules, and how the exploitation of novel niches may have driven the evolution of the multipartite genome. The aims of this review are to (i) outline the literature regarding bacterial genomes that are divided into multiple fragments, (ii) provide a meta-analysis of completed bacterial genomes from 1,708 species as a way of reviewing the abundant information present in these genome sequences, and (iii) provide an encompassing model to explain the evolution and function of the multipartite genome structure. This review covers, among other topics, salient genome terminology; mechanisms of multipartite genome formation; the phylogenetic distribution of multipartite genomes; how each part of a genome differs with respect to genomic signatures, genetic variability, and gene functional annotation; how each DNA molecule may interact; as well as the costs and benefits of this genome structure.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Turlough M Finan
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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19
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PhoU Allows Rapid Adaptation to High Phosphate Concentrations by Modulating PstSCAB Transport Rate in Sinorhizobium meliloti. J Bacteriol 2017; 199:JB.00143-17. [PMID: 28416708 DOI: 10.1128/jb.00143-17] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 04/11/2017] [Indexed: 01/14/2023] Open
Abstract
Maintenance of cellular phosphate homeostasis is essential for cellular life. The PhoU protein has emerged as a key regulator of this process in bacteria, and it is suggested to modulate phosphate import by PstSCAB and control activation of the phosphate limitation response by the PhoR-PhoB two-component system. However, a proper understanding of PhoU has remained elusive due to numerous complications of mutating phoU, including loss of viability and the genetic instability of the mutants. Here, we developed two sets of strains of Sinorhizobium meliloti that overcame these limitations and allowed a more detailed and comprehensive analysis of the biological and molecular activities of PhoU. The data showed that phoU cannot be deleted in the presence of phosphate unless PstSCAB is inactivated also. However, phoU deletions were readily recovered in phosphate-free media, and characterization of these mutants revealed that addition of phosphate to the environment resulted in toxic levels of PstSCAB-mediated phosphate accumulation. Phosphate uptake experiments indicated that PhoU significantly decreased the PstSCAB transport rate specifically in phosphate-replete cells but not in phosphate-starved cells and that PhoU could rapidly respond to elevated environmental phosphate concentrations and decrease the PstSCAB transport rate. Site-directed mutagenesis results suggested that the ability of PhoU to respond to phosphate levels was independent of the conformation of the PstSCAB transporter. Additionally, PhoU-PhoU and PhoU-PhoR interactions were detected using a bacterial two-hybrid screen. We propose that PhoU modulates PstSCAB and PhoR-PhoB in response to local, internal fluctuations in phosphate concentrations resulting from PstSCAB-mediated phosphate import.IMPORTANCE Correct maintenance of cellular phosphate homeostasis is critical in all kingdoms of life and in bacteria involves the PhoU protein. This work provides novel insights into the role of the Sinorhizobium meliloti PhoU protein, which plays a key role in rapid adaptation to elevated phosphate concentrations. It is shown that PhoU rapidly responds to elevated phosphate levels by significantly decreasing the phosphate transport of PstSCAB, thereby preventing phosphate toxicity and cell death. Additionally, a new model for phosphate sensing in bacterial species which involves the PhoR-PhoB two-component system is presented. This work provides new insights into the bacterial response to changing environmental conditions and into regulation of the phosphate limitation response that influences numerous bacterial processes, including antibiotic production and virulence.
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20
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An evolutionary perspective on plasmid lifestyle modes. Curr Opin Microbiol 2017; 38:74-80. [DOI: 10.1016/j.mib.2017.05.001] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 05/03/2017] [Accepted: 05/04/2017] [Indexed: 11/19/2022]
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21
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diCenzo GC, Zamani M, Ludwig HN, Finan TM. Heterologous Complementation Reveals a Specialized Activity for BacA in the Medicago-Sinorhizobium meliloti Symbiosis. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2017; 30:312-324. [PMID: 28398123 DOI: 10.1094/mpmi-02-17-0030-r] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The bacterium Sinorhizobium meliloti Rm2011 forms N2-fixing root nodules on alfalfa and other leguminous plants. The pSymB chromid contains a 110-kb region (the ETR region) showing high synteny to a chromosomally located region in Sinorhizobium fredii NGR234 and related rhizobia. We recently introduced the ETR region from S. fredii NGR234 into the S. meliloti chromosome. Here, we report that, unexpectedly, the S. fredii NGR234 ETR region did not complement deletion of the S. meliloti ETR region in symbiosis with Medicago sativa. This phenotype was due to the bacA gene of NGR234 not being functionally interchangeable with the S. meliloti bacA gene during M. sativa symbiosis. Further analysis revealed that, whereas bacA genes from S. fredii or Rhizobium leguminosarum bv. viciae 3841 failed to complement the Fix- phenotype of a S. meliloti bacA mutant with M. sativa, they allowed for further developmental progression prior to a loss of viability. In contrast, with Melilotus alba, bacA from S. fredii and R. leguminosarum supported N2 fixation by a S. meliloti bacA mutant. Additionally, the S. meliloti bacA gene can support N2 fixation of a R. leguminosarum bacA mutant during symbiosis with Pisum sativum. A phylogeny of BacA proteins illustrated that S. meliloti BacA has rapidly diverged from most rhizobia and has converged toward the sequence of pathogenic genera Brucella and Escherichia. These data suggest that the S. meliloti BacA has evolved toward a specific interaction with Medicago and highlights the limitations of using a single model system for the study of complex biological topics.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario L8S 4K1, Canada
| | - Maryam Zamani
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario L8S 4K1, Canada
| | - Hannah N Ludwig
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario L8S 4K1, Canada
| | - Turlough M Finan
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario L8S 4K1, Canada
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22
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Guo FB, Xiong L, Zhang KY, Dong C, Zhang FZ, Woo PCY. Identification and analysis of genomic islands in Burkholderia cenocepacia AU 1054 with emphasis on pathogenicity islands. BMC Microbiol 2017; 17:73. [PMID: 28347342 PMCID: PMC5369199 DOI: 10.1186/s12866-017-0986-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 03/18/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Genomic islands (GIs) are genomic regions that reveal evidence of horizontal DNA transfer. They can code for many functions and may augment a bacterium's adaptation to its host or environment. GIs have been identified in strain J2315 of Burkholderia cenocepacia, whereas in strain AU 1054 there has been no published works on such regions according to our text mining and keyword search in Medline. RESULTS In this study, we identified 21 GIs in AU 1054 by combining two computational tools. Feature analyses suggested that the predictions are highly reliable and hence illustrated the advantage of joint predictions by two independent methods. Based on putative virulence factors, four GIs were further identified as pathogenicity islands (PAIs). Through experiments of gene deletion mutants in live bacteria, two putative PAIs were confirmed, and the virulence factors involved were identified as lipA and copR. The importance of the genes lipA (from PAI 1) and copR (from PAI 2) for bacterial invasion and replication indicates that they are required for the invasive properties of B. cenocepacia and may function as virulence determinants for bacterial pathogenesis and host infection. CONCLUSIONS This approach of in silico prediction of GIs and subsequent identification of potential virulence factors in the putative island regions with final validation using wet experiments could be used as an effective strategy to rapidly discover novel virulence factors in other bacterial species and strains.
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Affiliation(s)
- Feng-Biao Guo
- School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Center for Informational Biology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Key Laboratory for Neuro-information of the Ministry of Education, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Department of Microbiology, The University of Hong Kong, Hong Kong, Special Administrative Region, People's Republic of China
| | - Lifeng Xiong
- Department of Microbiology, The University of Hong Kong, Hong Kong, Special Administrative Region, People's Republic of China
| | - Kai-Yue Zhang
- School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Center for Informational Biology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Key Laboratory for Neuro-information of the Ministry of Education, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Chuan Dong
- School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Center for Informational Biology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Key Laboratory for Neuro-information of the Ministry of Education, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Fa-Zhan Zhang
- School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Center for Informational Biology, University of Electronic Science and Technology of China, Chengdu, 610054, China.,Key Laboratory for Neuro-information of the Ministry of Education, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Patrick C Y Woo
- Department of Microbiology, The University of Hong Kong, Hong Kong, Special Administrative Region, People's Republic of China.
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23
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diCenzo GC, Checcucci A, Bazzicalupo M, Mengoni A, Viti C, Dziewit L, Finan TM, Galardini M, Fondi M. Metabolic modelling reveals the specialization of secondary replicons for niche adaptation in Sinorhizobium meliloti. Nat Commun 2016; 7:12219. [PMID: 27447951 PMCID: PMC4961836 DOI: 10.1038/ncomms12219] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 06/10/2016] [Indexed: 12/14/2022] Open
Abstract
The genome of about 10% of bacterial species is divided among two or more large chromosome-sized replicons. The contribution of each replicon to the microbial life cycle (for example, environmental adaptations and/or niche switching) remains unclear. Here we report a genome-scale metabolic model of the legume symbiont Sinorhizobium meliloti that is integrated with carbon utilization data for 1,500 genes with 192 carbon substrates. Growth of S. meliloti is modelled in three ecological niches (bulk soil, rhizosphere and nodule) with a focus on the role of each of its three replicons. We observe clear metabolic differences during growth in the tested ecological niches and an overall reprogramming following niche switching. In silico examination of the inferred fitness of gene deletion mutants suggests that secondary replicons evolved to fulfil a specialized function, particularly host-associated niche adaptation. Thus, genes on secondary replicons might potentially be manipulated to promote or suppress host interactions for biotechnological purposes. The genome of some bacteria consists of two or more chromosomes or replicons. Here, diCenzo et al. integrate genome-scale metabolic modelling and growth data from a collection of mutants of the plant symbiont Sinorhizobium meliloti to estimate the fitness contribution of each replicon in three environments.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 1A1
| | - Alice Checcucci
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Marco Bazzicalupo
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Alessio Mengoni
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Carlo Viti
- Department of Agri-food Production and Environmental Sciences, University of Florence, 50144 Sesto Fiorentino, Italy
| | - Lukasz Dziewit
- Department of Bacterial Genetics, Institute of Microbiology, Faculty of Biology, University of Warsaw, 02-096 Warsaw, Poland
| | - Turlough M Finan
- Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 1A1
| | - Marco Galardini
- EMBL-EBI, Wellcome Trust Genome Campus, Cambridge CB10 1SD, UK
| | - Marco Fondi
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
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24
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Hernández-Tamayo R, Torres-Tejerizo G, Brom S, Romero D. Site-specific bacterial chromosome engineering mediated by IntA integrase from Rhizobium etli. BMC Microbiol 2016; 16:133. [PMID: 27357704 PMCID: PMC4928290 DOI: 10.1186/s12866-016-0755-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 06/28/2016] [Indexed: 11/24/2022] Open
Abstract
Background The bacterial chromosome may be used to stably maintain foreign DNA in the mega-base range. Integration into the chromosome circumvents issues such as plasmid replication, stability, incompatibility, and copy number variance. The site-specific integrase IntA from Rhizobium etli CFN42 catalyzes a direct recombination between two specific DNA sites: attA and attD (23 bp). This recombination is stable. The aim of this work was to develop a R. etli derivative that may be used as recipient for the integration of foreign DNA in the chromosome, adapting the IntA catalyzed site-specific recombination system. Results To fulfill our aim, we designed a Rhizobium etli CFN42 derivative, containing a “landing pad” (LP) integrated into the chromosome. The LP sector consists of a green fluorescent protein gene under the control of the lacZ promoter and a spectinomycin resistance gene. Between the lacZ promoter and the GFP gene we inserted an IntA attachment site, which does not affect transcription from the lac promoter. Also, a mobilizable donor vector was generated, containing an attA site and a kanamycin resistance gene; to facilitate insertion of foreign DNA, this vector also contains a multicloning site. There are no promoters flanking the multicloning site. A biparental mating protocol was used to transfer the donor vector into the landing pad strain; insertion of the donor vector into the landing pad sector via IntA-mediated attA X attA recombination thereby interrupted the expression of the green fluorescent protein, generating site-specific cointegrants. Cointegrants were easily recognized by screening for antibiotic sensitivity and lack of GFP expression, and were obtained with an efficiency of 6.18 %. Conclusions Integration of foreign DNA in Rhizobium, lacking any similarity with the genome, can be easily achieved by IntA-mediated recombination. This protocol contains the mating and selection procedures for creating and isolating integrants.
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Affiliation(s)
- Rogelio Hernández-Tamayo
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico
| | - Gonzalo Torres-Tejerizo
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico.,Departamento de Ciencias Biológicas, Instituto de Biotecnología y Biología Molecular, UNLP, CCT-La Plata-CONICET, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Susana Brom
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico
| | - David Romero
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico.
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25
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Sanjuán J. Towards the minimal nitrogen-fixing symbiotic genome. Environ Microbiol 2016; 18:2292-4. [PMID: 27188818 DOI: 10.1111/1462-2920.13261] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 02/10/2016] [Indexed: 01/13/2023]
Abstract
diCenzo and coworkers have reverse engineered a rhizobium into a non-nitrogen fixer, creating a genomic platform for gain-of-function genetics studies, which should aid to identify the minimal nitrogen fixing symbiotic genome.
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Affiliation(s)
- Juan Sanjuán
- Depto. Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Prof. Albareda 1, 18008, Granada, Spain
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26
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diCenzo GC, Zamani M, Milunovic B, Finan TM. Genomic resources for identification of the minimal N2 -fixing symbiotic genome. Environ Microbiol 2016; 18:2534-47. [PMID: 26768651 DOI: 10.1111/1462-2920.13221] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 12/17/2015] [Accepted: 01/09/2016] [Indexed: 12/11/2022]
Abstract
The lack of an appropriate genomic platform has precluded the use of gain-of-function approaches to study the rhizobium-legume symbiosis, preventing the establishment of the genes necessary and sufficient for symbiotic nitrogen fixation (SNF) and potentially hindering synthetic biology approaches aimed at engineering this process. Here, we describe the development of an appropriate system by reverse engineering Sinorhizobium meliloti. Using a novel in vivo cloning procedure, the engA-tRNA-rmlC (ETR) region, essential for cell viability and symbiosis, was transferred from Sinorhizobium fredii to the ancestral location on the S. meliloti chromosome, rendering the ETR region on pSymB redundant. A derivative of this strain lacking both the large symbiotic replicons (pSymA and pSymB) was constructed. Transfer of pSymA and pSymB back into this strain restored symbiotic capabilities with alfalfa. To delineate the location of the single-copy genes essential for SNF on these replicons, we screened a S. meliloti deletion library, representing > 95% of the 2900 genes of the symbiotic replicons, for their phenotypes with alfalfa. Only four loci, accounting for < 12% of pSymA and pSymB, were essential for SNF. These regions will serve as our preliminary target of the minimal set of horizontally acquired genes necessary and sufficient for SNF.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
| | - Maryam Zamani
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
| | - Branislava Milunovic
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
| | - Turlough M Finan
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
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Geddes BA, Oresnik IJ. The Mechanism of Symbiotic Nitrogen Fixation. ADVANCES IN ENVIRONMENTAL MICROBIOLOGY 2016. [DOI: 10.1007/978-3-319-28068-4_4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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28
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Wetzel ME, Olsen GJ, Chakravartty V, Farrand SK. The repABC Plasmids with Quorum-Regulated Transfer Systems in Members of the Rhizobiales Divide into Two Structurally and Separately Evolving Groups. Genome Biol Evol 2015; 7:3337-57. [PMID: 26590210 PMCID: PMC4700958 DOI: 10.1093/gbe/evv227] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The large repABC plasmids of the order Rhizobiales with Class I quorum-regulated conjugative transfer systems often define the nature of the bacterium that harbors them. These otherwise diverse plasmids contain a core of highly conserved genes for replication and conjugation raising the question of their evolutionary relationships. In an analysis of 18 such plasmids these elements fall into two organizational classes, Group I and Group II, based on the sites at which cargo DNA is located. Cladograms constructed from proteins of the transfer and quorum-sensing components indicated that those of the Group I plasmids, while coevolving, have diverged from those coevolving proteins of the Group II plasmids. Moreover, within these groups the phylogenies of the proteins usually occupy similar, if not identical, tree topologies. Remarkably, such relationships were not seen among proteins of the replication system; although RepA and RepB coevolve, RepC does not. Nor do the replication proteins coevolve with the proteins of the transfer and quorum-sensing systems. Functional analysis was mostly consistent with phylogenies. TraR activated promoters from plasmids within its group, but not between groups and dimerized with TraR proteins from within but not between groups. However, oriT sequences, which are highly conserved, were processed by the transfer system of plasmids regardless of group. We conclude that these plasmids diverged into two classes based on the locations at which cargo DNA is inserted, that the quorum-sensing and transfer functions are coevolving within but not between the two groups, and that this divergent evolution extends to function.
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Affiliation(s)
- Margaret E Wetzel
- Department of Microbiology, University of Illinois at Urbana-Champaign
| | - Gary J Olsen
- Department of Microbiology, University of Illinois at Urbana-Champaign Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign
| | | | - Stephen K Farrand
- Department of Microbiology, University of Illinois at Urbana-Champaign
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Vinardell JM, Acosta-Jurado S, Zehner S, Göttfert M, Becker A, Baena I, Blom J, Crespo-Rivas JC, Goesmann A, Jaenicke S, Krol E, McIntosh M, Margaret I, Pérez-Montaño F, Schneiker-Bekel S, Serranía J, Szczepanowski R, Buendía AM, Lloret J, Bonilla I, Pühler A, Ruiz-Sainz JE, Weidner S. The Sinorhizobium fredii HH103 Genome: A Comparative Analysis With S. fredii Strains Differing in Their Symbiotic Behavior With Soybean. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2015; 28:811-24. [PMID: 25675256 DOI: 10.1094/mpmi-12-14-0397-fi] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Sinorhizobium fredii HH103 is a fast-growing rhizobial strain infecting a broad range of legumes including both American and Asiatic soybeans. In this work, we present the sequencing and annotation of the HH103 genome (7.25 Mb), consisting of one chromosome and six plasmids and representing the structurally most complex sinorhizobial genome sequenced so far. Comparative genomic analyses of S. fredii HH103 with strains USDA257 and NGR234 showed that the core genome of these three strains contains 4,212 genes (61.7% of the HH103 genes). Synteny plot analysis revealed that the much larger chromosome of USDA257 (6.48 Mb) is colinear to the HH103 (4.3 Mb) and NGR324 chromosomes (3.9 Mb). An additional region of the USDA257 chromosome of about 2 Mb displays similarity to plasmid pSfHH103e. Remarkable differences exist between HH103 and NGR234 concerning nod genes, flavonoid effect on surface polysaccharide production, and quorum-sensing systems. Furthermore a number of protein secretion systems have been found. Two genes coding for putative type III-secreted effectors not previously described in S. fredii, nopI and gunA, have been located on the HH103 genome. These differences could be important to understand the different symbiotic behavior of S. fredii strains HH103, USDA257, and NGR234 with soybean.
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Affiliation(s)
- José-María Vinardell
- 1 Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla. Avda. Reina Mercedes 6, C.P. 41012 Sevilla, Spain
| | - Sebastián Acosta-Jurado
- 1 Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla. Avda. Reina Mercedes 6, C.P. 41012 Sevilla, Spain
| | - Susanne Zehner
- 2 Technische Universität Dresden, Institut für Genetik, Helmholtzstrasse 10, 01062 Dresden, Germany
| | - Michael Göttfert
- 2 Technische Universität Dresden, Institut für Genetik, Helmholtzstrasse 10, 01062 Dresden, Germany
| | - Anke Becker
- 3 LOEWE Center for Synthetic Microbiology (SYNMIKRO) and Faculty of Biology, Philipps-Universität Marburg, Hans-Meerwein-Str. 6, 35043 Marburg, Germany
| | - Irene Baena
- 4 Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049-Madrid, Spain
| | - Jochem Blom
- 5 Centrum für Biotechnologie (CeBiTec), Universität Bielefeld, Universitaetsstr. 27, 33615 Bielefeld, Germany
| | - Juan Carlos Crespo-Rivas
- 1 Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla. Avda. Reina Mercedes 6, C.P. 41012 Sevilla, Spain
| | - Alexander Goesmann
- 5 Centrum für Biotechnologie (CeBiTec), Universität Bielefeld, Universitaetsstr. 27, 33615 Bielefeld, Germany
| | - Sebastian Jaenicke
- 5 Centrum für Biotechnologie (CeBiTec), Universität Bielefeld, Universitaetsstr. 27, 33615 Bielefeld, Germany
| | - Elizaveta Krol
- 3 LOEWE Center for Synthetic Microbiology (SYNMIKRO) and Faculty of Biology, Philipps-Universität Marburg, Hans-Meerwein-Str. 6, 35043 Marburg, Germany
| | - Matthew McIntosh
- 3 LOEWE Center for Synthetic Microbiology (SYNMIKRO) and Faculty of Biology, Philipps-Universität Marburg, Hans-Meerwein-Str. 6, 35043 Marburg, Germany
| | - Isabel Margaret
- 1 Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla. Avda. Reina Mercedes 6, C.P. 41012 Sevilla, Spain
| | - Francisco Pérez-Montaño
- 1 Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla. Avda. Reina Mercedes 6, C.P. 41012 Sevilla, Spain
| | - Susanne Schneiker-Bekel
- 5 Centrum für Biotechnologie (CeBiTec), Universität Bielefeld, Universitaetsstr. 27, 33615 Bielefeld, Germany
| | - Javier Serranía
- 3 LOEWE Center for Synthetic Microbiology (SYNMIKRO) and Faculty of Biology, Philipps-Universität Marburg, Hans-Meerwein-Str. 6, 35043 Marburg, Germany
| | - Rafael Szczepanowski
- 5 Centrum für Biotechnologie (CeBiTec), Universität Bielefeld, Universitaetsstr. 27, 33615 Bielefeld, Germany
| | - Ana-María Buendía
- 1 Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla. Avda. Reina Mercedes 6, C.P. 41012 Sevilla, Spain
| | - Javier Lloret
- 4 Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049-Madrid, Spain
| | - Ildefonso Bonilla
- 4 Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049-Madrid, Spain
| | - Alfred Pühler
- 5 Centrum für Biotechnologie (CeBiTec), Universität Bielefeld, Universitaetsstr. 27, 33615 Bielefeld, Germany
| | - José-Enrique Ruiz-Sainz
- 1 Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla. Avda. Reina Mercedes 6, C.P. 41012 Sevilla, Spain
| | - Stefan Weidner
- 5 Centrum für Biotechnologie (CeBiTec), Universität Bielefeld, Universitaetsstr. 27, 33615 Bielefeld, Germany
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Molina-Sánchez MD, López-Contreras JA, Toro N, Fernández-López M. Genomic characterization of Sinorhizobium meliloti AK21, a wild isolate from the Aral Sea Region. SPRINGERPLUS 2015; 4:259. [PMID: 26090306 PMCID: PMC4468178 DOI: 10.1186/s40064-015-1062-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Accepted: 05/26/2015] [Indexed: 11/10/2022]
Abstract
The symbiotic, nitrogen-fixing bacterium Sinorhizobium meliloti has been widely studied due to its ability to improve crop yields through direct interactions with leguminous plants. S. meliloti AK21 is a wild type strain that forms nodules on Medicago plants in saline and drought conditions in the Aral Sea Region. The aim of this work was to establish the genetic similarities and differences between S. meliloti AK21 and the reference strain S. meliloti 1021. Comparative genome hybridization with the model reference strain S. meliloti 1021 yielded 365 variable genes, grouped into 11 regions in the three main replicons in S. meliloti AK21. The most extensive regions of variability were found in the symbiotic plasmid pSymA, which also contained the largest number of orthologous and polymorphic sequences identified by suppression subtractive hybridization. This procedure identified a large number of divergent sequences and others without homology in the databases, the further investigation of which could provide new insight into the alternative metabolic pathways present in S. meliloti AK21. We identified a plasmid replication module from the repABC replicon family, together with plasmid mobilization-related genes (traG and a VirB9-like protein), which suggest that this indigenous isolate harbors an accessory plasmid. Furthermore, the transcriptomic profiles reflected differences in gene content and regulation between S. meliloti AK21 and S. meliloti 1021 (ExpR and PhoB regulons), but provided evidence for an as yet unknown, alternative mechanism involving activation of the cbb3 terminal oxidase. Finally, phenotypic microarrays characterization revealed a greater versatility of substrate use and chemical degradation than for S. meliloti 1021.
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Affiliation(s)
- María Dolores Molina-Sánchez
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
| | - José Antonio López-Contreras
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
| | - Nicolás Toro
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
| | - Manuel Fernández-López
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
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31
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diCenzo GC, Finan TM. Genetic redundancy is prevalent within the 6.7 Mb Sinorhizobium meliloti genome. Mol Genet Genomics 2015; 290:1345-56. [PMID: 25638282 DOI: 10.1007/s00438-015-0998-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 01/17/2015] [Indexed: 01/09/2023]
Abstract
Biological pathways are frequently identified via a genetic loss-of-function approach. While this approach has proven to be powerful, it is imperfect as illustrated by well-studied pathways continuing to have missing steps. One potential limiting factor is the masking of phenotypes through genetic redundancy. The prevalence of genetic redundancy in bacterial species has received little attention, although isolated examples of functionally redundant gene pairs exist. Here, we made use of a strain of Sinorhizobium meliloti whose genome was reduced by 45 % through the complete removal of a megaplasmid and a chromid (3 Mb of the 6.7 Mb genome was removed) to begin quantifying the level of genetic redundancy within a large bacterial genome. A mutagenesis of the strain with the reduced genome identified a set of transposon insertions precluding growth of this strain on minimal medium. Transfer of these mutations to the wild-type background revealed that 10-15 % of these chromosomal mutations were located within duplicated genes, as they did not prevent growth of cells with the full genome. The functionally redundant genes were involved in a variety of metabolic pathways, including central carbon metabolism, transport, and amino acid biosynthesis. These results indicate that genetic redundancy may be prevalent within large bacterial genomes. Failing to account for redundantly encoded functions in loss-of-function studies will impair our understanding of a broad range of biological processes and limit our ability to use synthetic biology in the construction of designer cell factories.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON, L8S 4K1, Canada
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diCenzo GC, MacLean AM, Milunovic B, Golding GB, Finan TM. Examination of prokaryotic multipartite genome evolution through experimental genome reduction. PLoS Genet 2014; 10:e1004742. [PMID: 25340565 PMCID: PMC4207669 DOI: 10.1371/journal.pgen.1004742] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Accepted: 09/08/2014] [Indexed: 01/12/2023] Open
Abstract
Many bacteria carry two or more chromosome-like replicons. This occurs in pathogens such as Vibrio cholerea and Brucella abortis as well as in many N2-fixing plant symbionts including all isolates of the alfalfa root-nodule bacteria Sinorhizobium meliloti. Understanding the evolution and role of this multipartite genome organization will provide significant insight into these important organisms; yet this knowledge remains incomplete, in part, because technical challenges of large-scale genome manipulations have limited experimental analyses. The distinct evolutionary histories and characteristics of the three replicons that constitute the S. meliloti genome (the chromosome (3.65 Mb), pSymA megaplasmid (1.35 Mb), and pSymB chromid (1.68 Mb)) makes this a good model to examine this topic. We transferred essential genes from pSymB into the chromosome, and constructed strains that lack pSymB as well as both pSymA and pSymB. This is the largest reduction (45.4%, 3.04 megabases, 2866 genes) of a prokaryotic genome to date and the first removal of an essential chromid. Strikingly, strains lacking pSymA and pSymB (ΔpSymAB) lost the ability to utilize 55 of 74 carbon sources and various sources of nitrogen, phosphorous and sulfur, yet the ΔpSymAB strain grew well in minimal salts media and in sterile soil. This suggests that the core chromosome is sufficient for growth in a bulk soil environment and that the pSymA and pSymB replicons carry genes with more specialized functions such as growth in the rhizosphere and interaction with the plant. These experimental data support a generalized evolutionary model, in which non-chromosomal replicons primarily carry genes with more specialized functions. These large secondary replicons increase the organism's niche range, which offsets their metabolic burden on the cell (e.g. pSymA). Subsequent co-evolution with the chromosome then leads to the formation of a chromid through the acquisition of functions core to all niches (e.g. pSymB). Rhizobia are free-living bacteria of agricultural and environmental importance that form root-nodules on leguminous plants and provide these plants with fixed nitrogen. Many of the rhizobia have a multipartite genome, as do several plant and animal pathogens. All isolates of the alfalfa symbiont, Sinorhizobium meliloti, carry three large replicons, the chromosome (∼3.7 Mb), pSymA megaplasmid (∼1.4 Mb), and pSymB chromid (∼1.7 Mb). To gain insight into the role and evolutionary history of these replicons, we have ‘reversed evolution’ by constructing a S. meliloti strain consisting solely of the chromosome and lacking the pSymB chromid and pSymA megaplasmid. As the resulting strain was viable, we could perform a detailed phenotypic analysis and these data provided significant insight into the biology and metabolism of S. meliloti. The data lend direct experimental evidence in understanding the evolution and role of the multipartite genome. Specifically the large secondary replicons increase the organism's niche range, and this advantage offsets the metabolic burden of these replicons on the cell. Additionally, the single-chromosome strain offers a useful platform to facilitate future forward genetic approaches to understanding and manipulating the symbiosis and plant-microbe interactions.
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Affiliation(s)
- George C. diCenzo
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | | | | | - G. Brian Golding
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Turlough M. Finan
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
- * E-mail:
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Stasiak G, Mazur A, Wielbo J, Marczak M, Zebracki K, Koper P, Skorupska A. Functional relationships between plasmids and their significance for metabolism and symbiotic performance of Rhizobium leguminosarum bv. trifolii. J Appl Genet 2014; 55:515-27. [PMID: 24839164 PMCID: PMC4185100 DOI: 10.1007/s13353-014-0220-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 04/11/2014] [Accepted: 04/30/2014] [Indexed: 12/31/2022]
Abstract
Rhizobium leguminosarum bv. trifolii TA1 (RtTA1) is a soil bacterium establishing a highly specific symbiotic relationship with clover, which is based on the exchange of molecular signals between the host plant and the microsymbiont. The RtTA1 genome is large and multipartite, composed of a chromosome and four plasmids, which comprise approximately 65 % and 35 % of the total genome, respectively. Extrachromosomal replicons were previously shown to confer significant metabolic versatility to bacteria, which is important for their adaptation in the soil and nodulation competitiveness. To investigate the contribution of individual RtTA1 plasmids to the overall cell phenotype, metabolic properties and symbiotic performance, a transposon-based elimination strategy was employed. RtTA1 derivatives cured of pRleTA1b or pRleTA1d and deleted in pRleTA1a were obtained. In contrast to the in silico predictions of pRleTA1b and pRleTA1d, which were described as chromid-like replicons, both appeared to be completely curable. On the other hand, for pRleTA1a (symbiotic plasmid) and pRleTA1c, which were proposed to be unessential for RtTA1 viability, it was not possible to eliminate them at all (pRleTA1c) or entirely (pRleTA1a). Analyses of the phenotypic traits of the RtTA1 derivatives obtained revealed the functional significance of individual plasmids and their indispensability for growth, certain metabolic pathways, production of surface polysaccharides, autoaggregation, biofilm formation, motility and symbiotic performance. Moreover, the results allow us to suggest broad functional cooperation among the plasmids in shaping the phenotypic properties and symbiotic capabilities of rhizobia.
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Affiliation(s)
- Grażyna Stasiak
- Department of Genetics and Microbiology, Maria-Curie Skłodowska University, 19 Akademicka St., 20-033, Lublin, Poland
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Cell growth inhibition upon deletion of four toxin-antitoxin loci from the megaplasmids of Sinorhizobium meliloti. J Bacteriol 2013; 196:811-24. [PMID: 24317400 DOI: 10.1128/jb.01104-13] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Toxin and antitoxin (TA) gene pairs are addiction systems that are present in many microbial genomes. Sinorhizobium meliloti is an N2-fixing bacterial symbiont of alfalfa and other leguminous plants, and its genome consists of three large replicons, a circular chromosome (3.7 Mb) and the megaplasmids pSymA (1.4 Mb) and pSymB (1.7 Mb). S. meliloti carries 211 predicted type II TA genes, each encoding a toxin or an antitoxin. We constructed defined deletion strains that collectively removed the entire pSymA and pSymB megaplasmids except for their oriV regions. Of approximately 100 TA genes on pSymA and pSymB, we identified four whose loss was associated with cell death or stasis unless copies of the genes were supplied in trans. Orthologs of three of these loci have been characterized in other organisms (relB/E [sma0471/sma0473], Fic [DOC] [sma2105], and VapC [PIN] [orf2230/sma2231]), and this report contains the first experimental proof that RES/Xre (smb21127/smb21128) loci can function as a TA system. Transcriptome sequencing (RNA-seq) analysis did not reveal transcriptional differences between the TA systems to account for why deletion of the four "active" systems resulted in cell toxicity. These data suggest that severe cell growth phenotypes result from the loss of a few TA systems and that loss of most TA systems may result in more subtle phenotypes. These four TA systems do not appear to play a direct role in the S. meliloti-alfalfa symbiosis, as strains lacking these TA systems had a symbiotic N2 fixation phenotype that was indistinguishable from the wild type.
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