1
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Peng N, Cai P, Mortimer M, Wu Y, Gao C, Huang Q. The exopolysaccharide-eDNA interaction modulates 3D architecture of Bacillus subtilis biofilm. BMC Microbiol 2020; 20:115. [PMID: 32410574 PMCID: PMC7227074 DOI: 10.1186/s12866-020-01789-5] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 04/16/2020] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND Bacterial biofilms are surface-adherent microbial communities in which individual cells are surrounded by a self-produced extracellular matrix of polysaccharides, extracellular DNA (eDNA) and proteins. Interactions among matrix components within biofilms are responsible for creating an adaptable structure during biofilm development. However, it is unclear how the interactions among matrix components contribute to the construction of the three-dimensional (3D) biofilm architecture. RESULTS DNase I treatment significantly inhibited Bacillus subtilis biofilm formation in the early phases of biofilm development. Confocal laser scanning microscopy (CLSM) and image analysis revealed that eDNA was cooperative with exopolysaccharide (EPS) in the early stages of B. subtilis biofilm development, while EPS played a major structural role in the later stages. In addition, deletion of the EPS production gene epsG in B. subtilis SBE1 resulted in loss of the interaction between EPS and eDNA and reduced the biofilm biomass in pellicles at the air-liquid interface. The physical interaction between these two essential biofilm matrix components was confirmed by isothermal titration calorimetry (ITC). CONCLUSIONS Biofilm 3D structures become interconnected through surrounding eDNA and EPS. eDNA interacts with EPS in the early phases of biofilm development, while EPS mainly participates in the maturation of biofilms. The findings of this study provide a better understanding of the role of the interaction between eDNA and EPS in shaping the biofilm 3D matrix structure and biofilm formation.
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Affiliation(s)
- Na Peng
- State Key Laboratory of Agricultural Microbiology, College of Resources of Environment, Huazhong Agricultural University, Wuhan, 430070 China
| | - Peng Cai
- State Key Laboratory of Agricultural Microbiology, College of Resources of Environment, Huazhong Agricultural University, Wuhan, 430070 China
| | - Monika Mortimer
- Bren School of Environmental Science and Management and Earth Research Institute, University of California, Santa Barbara, California, 93106 USA
| | - Yichao Wu
- State Key Laboratory of Agricultural Microbiology, College of Resources of Environment, Huazhong Agricultural University, Wuhan, 430070 China
| | - Chunhui Gao
- State Key Laboratory of Agricultural Microbiology, College of Resources of Environment, Huazhong Agricultural University, Wuhan, 430070 China
| | - Qiaoyun Huang
- State Key Laboratory of Agricultural Microbiology, College of Resources of Environment, Huazhong Agricultural University, Wuhan, 430070 China
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2
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Stress-Induced, Highly Efficient, Donor Cell-Dependent Cell-to-Cell Natural Transformation in Bacillus subtilis. J Bacteriol 2018; 200:JB.00267-18. [PMID: 29941421 DOI: 10.1128/jb.00267-18] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Accepted: 06/14/2018] [Indexed: 11/20/2022] Open
Abstract
Horizontal gene transfer (HGT) is a driving force for bacterial evolution that occurs via conjugation, transduction, and transformation. Whereas conjugation and transduction depend on nonbacterial vehicles, transformation is considered a naturally occurring process in which naked DNA molecules are taken up by a competent recipient cell. Here, we report that HGT occurred between two Bacillus subtilis strains cocultured on a minimum medium agar plate for 10 h. This process was almost completely resistant to DNase treatment and appeared to require close proximity between cells. The deletion of comK in the recipient completely abolished gene transfer, indicating that the process involved transformation. This process was also highly efficient, reaching 1.75 × 106 transformants/μg DNA compared to 5.3 × 103 and 1.86 × 105 transformants/μg DNA for DNA-to-cell transformation by the same agar method and the standard two-step procedure, respectively. Interestingly, when three distantly localized chromosomal markers were selected simultaneously, the efficiency of cell-to-cell transformation still reached 6.26 × 104 transformants/μg DNA, whereas no transformants were obtained when free DNA was used as the donor. Stresses, such as starvation and exposure to antibiotics, further enhanced transformation efficiency by affecting the donor cells, suggesting that stress served as an important signal for promoting this type of HGT. Taken together, our results defined a bona fide process of cell-to-cell natural transformation (CTCNT) in B. subtilis and related species. This finding reveals the previously unrecognized role of donor cells in bacterial natural transformation and improves our understanding of how HGT drives bacterial evolution at a mechanistic level.IMPORTANCE Because DNA is easily prepared, studies of bacterial natural genetic transformation traditionally focus on recipient cells. However, such laboratory artifacts cannot explain how this process occurs in nature. In most cases, competence is only transient and involves approximately 20 to 50 genes, and it is unreasonable for bacteria to spend so many genetic resources on unpredictable and uncertain environmental DNA. Here, we characterized a donor cell-dependent CTCNT process in B. subtilis and related species that was almost completely resistant to DNase treatment and was more efficient than classical natural transformation using naked DNA as a donor, i.e., DNA-to-cell transformation, suggesting that DNA donor cells were also important in the transformation process in natural environments.
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3
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Ibáñez de Aldecoa AL, Zafra O, González-Pastor JE. Mechanisms and Regulation of Extracellular DNA Release and Its Biological Roles in Microbial Communities. Front Microbiol 2017; 8:1390. [PMID: 28798731 PMCID: PMC5527159 DOI: 10.3389/fmicb.2017.01390] [Citation(s) in RCA: 177] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Accepted: 07/10/2017] [Indexed: 12/14/2022] Open
Abstract
The capacity to release genetic material into the extracellular medium has been reported in cultures of numerous species of bacteria, archaea, and fungi, and also in the context of multicellular microbial communities such as biofilms. Moreover, extracellular DNA (eDNA) of microbial origin is widespread in natural aquatic and terrestrial environments. Different specific mechanisms are involved in eDNA release, such as autolysis and active secretion, as well as through its association with membrane vesicles. It is noteworthy that in microorganisms, in which DNA release has been studied in detail, the production of eDNA is coordinated by the population when it reaches a certain cell density, and is induced in a subpopulation in response to the accumulation of quorum sensing signals. Interestingly, in several bacteria there is also a relationship between eDNA release and the development of natural competence (the ability to take up DNA from the environment), which is also controlled by quorum sensing. Then, what is the biological function of eDNA? A common biological role has not been proposed, since different functions have been reported depending on the microorganism. However, it seems to be important in biofilm formation, can be used as a nutrient source, and could be involved in DNA damage repair and gene transfer. This review covers several aspects of eDNA research: (i) its occurrence and distribution in natural environments, (ii) the mechanisms and regulation of its release in cultured microorganisms, and (iii) its biological roles. In addition, we propose that eDNA release could be considered a social behavior, based on its quorum sensing-dependent regulation and on the described functions of eDNA in the context of microbial communities.
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Affiliation(s)
- Alejandra L Ibáñez de Aldecoa
- Laboratory of Molecular Adaptation, Department of Molecular Evolution, Centro de Astrobiología (Consejo Superior de Investigaciones Científicas/Instituto Nacional de Técnica Aeroespacial)Madrid, Spain
| | - Olga Zafra
- Experimental Sciences Faculty, Francisco de Vitoria UniversityMadrid, Spain
| | - José E González-Pastor
- Laboratory of Molecular Adaptation, Department of Molecular Evolution, Centro de Astrobiología (Consejo Superior de Investigaciones Científicas/Instituto Nacional de Técnica Aeroespacial)Madrid, Spain
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4
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Characterization of hydrogen peroxide-induced DNA release by Streptococcus sanguinis and Streptococcus gordonii. J Bacteriol 2009; 191:6281-91. [PMID: 19684131 DOI: 10.1128/jb.00906-09] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Extracellular DNA (eDNA) is produced by several bacterial species and appears to contribute to biofilm development and cell-cell adhesion. We present data showing that the oral commensals Streptococcus sanguinis and Streptococcus gordonii release DNA in a process induced by pyruvate oxidase-dependent production of hydrogen peroxide (H(2)O(2)). Surprisingly, S. sanguinis and S. gordonii cell integrity appears unaffected by conditions that cause autolysis in other eDNA-producing bacteria. Exogenous H(2)O(2) causes release of DNA from S. sanguinis and S. gordonii but does not result in obvious lysis of cells. Under DNA-releasing conditions, cell walls appear functionally intact and ribosomes are retained over time. During DNA release, intracellular RNA and ATP are not coreleased. Hence, the release mechanism appears to be highly specific for DNA. Release of DNA without detectable autolysis is suggested to be an adaptation to the competitive oral biofilm environment, where autolysis could create open spaces for competitors to invade. Since eDNA promotes cell-to-cell adhesion, release appears to support oral biofilm formation and facilitates exchange of genetic material among competent strains.
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5
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Michod RE, Bernstein H, Nedelcu AM. Adaptive value of sex in microbial pathogens. INFECTION GENETICS AND EVOLUTION 2008; 8:267-85. [PMID: 18295550 DOI: 10.1016/j.meegid.2008.01.002] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 12/30/2007] [Accepted: 01/02/2008] [Indexed: 12/16/2022]
Abstract
Explaining the adaptive value of sex is one of the great outstanding problems in biology. The challenge comes from the difficulty in identifying the benefits provided by sex, which must outweigh the substantial costs of sex. Here, we consider the adaptive value of sex in viruses, bacteria and fungi, and particularly the information available on the adaptive role of sex in pathogenic microorganisms. Our general theme is that the varied aspects of sex in pathogens illustrate the varied issues surrounding the evolution of sex generally. These include, the benefits of sex (in the short- and long-term), as well as the costs of sex (both to the host and to the pathogen). For the benefits of sex (that is, its adaptive value), we consider three hypotheses: (i) sex provides for effective and efficient recombinational repair of DNA damages, (ii) sex provides DNA for food, and (iii) sex produces variation and reduces genetic associations among alleles under selection. Although the evolution of sex in microbial pathogens illustrates these general issues, our paper is not a general review of theories for the evolution of sex in all organisms. Rather, we focus on the adaptive value of sex in microbial pathogens and conclude that in terms of short-term benefits, the DNA repair hypothesis has the most support and is the most generally applicable hypothesis in this group. In particular, recombinational repair of DNA damages may substantially benefit pathogens when challenged by the oxidative defenses of the host. However, in the long-term, sex may help get rid of mutations, increase the rate of adaptation of the population, and, in pathogens, may infrequently create new infective strains. An additional general issue about sex illustrated by pathogens is that some of the most interesting consequences of sex are not necessarily the reasons for which sex evolved. For example, antibiotic resistance may be transferred by bacterial sex, but this transfer is probably not the reason sex evolved in bacteria.
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Affiliation(s)
- Richard E Michod
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson 85721, USA.
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6
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Ishii N, Matsui K, Fuma S, Takeda H, Kawabata Z. Release of transforming plasmid DNA from actively growing genetically engineeredEscherichia coli. FEMS Microbiol Lett 2004; 240:151-4. [PMID: 15522502 DOI: 10.1016/j.femsle.2004.09.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2004] [Revised: 09/16/2004] [Accepted: 09/21/2004] [Indexed: 11/17/2022] Open
Abstract
We studied the transforming ability of the extracellular plasmid DNA released from a genetically engineered Escherichia coli pEGFP and the culturing conditions for the release of transforming DNA. The transforming ability was evaluated by transformation of competent cells with filtrates of E. coli pEGFP cultures. The number of transformants increased with time when E. coli pEGFP cells grew exponentially in rich medium, but not in stationary phase or when inoculated in freshwater. These results suggested that crude extracellular plasmid DNA had transforming ability and this transforming DNA was mainly released by actively growing bacteria.
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Affiliation(s)
- Nobuyoshi Ishii
- Environmental and Toxicological Sciences Research Group, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
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7
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Cvitkovitch DG. Genetic competence and transformation in oral streptococci. CRITICAL REVIEWS IN ORAL BIOLOGY AND MEDICINE : AN OFFICIAL PUBLICATION OF THE AMERICAN ASSOCIATION OF ORAL BIOLOGISTS 2001; 12:217-43. [PMID: 11497374 DOI: 10.1177/10454411010120030201] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The oral streptococci are normally non-pathogenic residents of the human microflora. There is substantial evidence that these bacteria can, however, act as "genetic reservoirs" and transfer genetic information to transient bacteria as they make their way through the mouth, the principal entry point for a wide variety of bacteria. Examples that are of particular concern include the transfer of antibiotic resistance from oral streptococci to Streptococcus pneumoniae. The mechanisms that are used by oral streptococci to exchange genetic information are not well-understood, although several species are known to enter a physiological state of genetic competence. This state permits them to become capable of natural genetic transformation, facilitating the acquisition of foreign DNA from the external environment. The oral streptococci share many similarities with two closely related Gram-positive bacteria, S. pneumoniae and Bacillus subtilis. In these bacteria, the mechanisms of quorum-sensing, the development of competence, and DNA uptake and integration are well-characterized. Using this knowledge and the data available in genome databases allowed us to identify putative genes involved in these processes in the oral organism Streptococcus mutans. Models of competence development and genetic transformation in the oral streptococci and strategies to confirm these models are discussed. Future studies of competence in oral biofilms, the natural environment of oral streptococci, will be discussed.
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Affiliation(s)
- D G Cvitkovitch
- Dental Research Institute, University of Toronto, Faculty of Dentistry, ON, Canada.
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8
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Vettori C, Paffetti D, Pietramellara G, Stotzky G, Gallori E. Amplification of bacterial DNA bound on clay minerals by the random amplified polymorphic DNA (RAPD) technique. FEMS Microbiol Ecol 1996. [DOI: 10.1111/j.1574-6941.1996.tb00323.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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9
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Lorenz MG, Wackernagel W. Bacterial gene transfer by natural genetic transformation in the environment. Microbiol Rev 1994; 58:563-602. [PMID: 7968924 PMCID: PMC372978 DOI: 10.1128/mr.58.3.563-602.1994] [Citation(s) in RCA: 462] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Natural genetic transformation is the active uptake of free DNA by bacterial cells and the heritable incorporation of its genetic information. Since the famous discovery of transformation in Streptococcus pneumoniae by Griffith in 1928 and the demonstration of DNA as the transforming principle by Avery and coworkers in 1944, cellular processes involved in transformation have been studied extensively by in vitro experimentation with a few transformable species. Only more recently has it been considered that transformation may be a powerful mechanism of horizontal gene transfer in natural bacterial populations. In this review the current understanding of the biology of transformation is summarized to provide the platform on which aspects of bacterial transformation in water, soil, and sediments and the habitat of pathogens are discussed. Direct and indirect evidence for gene transfer routes by transformation within species and between different species will be presented, along with data suggesting that plasmids as well as chromosomal DNA are subject to genetic exchange via transformation. Experiments exploring the prerequisites for transformation in the environment, including the production and persistence of free DNA and factors important for the uptake of DNA by cells, will be compiled, as well as possible natural barriers to transformation. The efficiency of gene transfer by transformation in bacterial habitats is possibly genetically adjusted to submaximal levels. The fact that natural transformation has been detected among bacteria from all trophic and taxonomic groups including archaebacteria suggests that transformability evolved early in phylogeny. Probable functions of DNA uptake other than gene acquisition will be discussed. The body of information presently available suggests that transformation has a great impact on bacterial population dynamics as well as on bacterial evolution and speciation.
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Affiliation(s)
- M G Lorenz
- Genetik, Fachbereich Biologie, Carl-von-Ossietzky Universität Oldenburg, Germany
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10
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Romanowski G, Lorenz MG, Wackernagel W. Use of polymerase chain reaction and electroporation of Escherichia coli to monitor the persistence of extracellular plasmid DNA introduced into natural soils. Appl Environ Microbiol 1993; 59:3438-46. [PMID: 8250566 PMCID: PMC182471 DOI: 10.1128/aem.59.10.3438-3446.1993] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
A modified protocol for DNA amplification by polymerase chain reaction (PCR) coupled with laser densitometric determination of the amount of PCR products, which allowed quantitation of target sequence numbers in soil extracts, was developed. The method was applied to monitor target loss during incubation of purified plasmid DNA in natural nonsterile soils. It revealed soil-specific kinetics of target loss. After 60 days, 0.2, 0.05, and 0.01% of the initially added nahA genes on plasmids were detectable by PCR in a loamy sand soil, a clay soil, and a silty clay soil, respectively. Electroporation of Escherichia coli was used in parallel to quantitate plasmid molecules in soil extracts by their transforming activity. It was found that transformation by electroporation was about 20 times more efficient and much less inhibited by constituents of soil extracts than transformation of Ca(2+)-treated cells (G. Romanowski, M.G. Lorenz, G. Sayler, and W. Wackernagel, Appl. Environ. Microbiol. 58:3012-3019, 1992). By electroporation, greater than 10,000-fold plasmid loss was monitored in nonsterile soils. Transforming activity was found up to 60 days after inoculation of the soils. The studies indicate that PCR and electroporation are sensitive methods for monitoring the persistence of extracellular plasmid DNA in soil. It is proposed that plasmid transformation by electroporation can be used for the monitoring in soil and other environments of genetically engineered organisms with recombinant plasmids. The data suggest that genetic material may persist in soil for weeks and even for months after its release from cells.
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Affiliation(s)
- G Romanowski
- Genetik, Fachbereich Biologie, Universität Oldenburg, Germany
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11
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Romanowski G, Lorenz MG, Wackernagel W. Plasmid DNA in a groundwater aquifer microcosm--adsorption, DNAase resistance and natural genetic transformation of Bacillus subtilis. Mol Ecol 1993; 2:171-81. [PMID: 8167851 DOI: 10.1111/j.1365-294x.1993.tb00106.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Prokaryotes can exchange chromosomal and plasmid genes via extracellular DNA in a process termed genetic transformation. This process has been observed in the test tube for several bacterial species living in the environment but it is not clear whether transformation occurs in natural bacterial habitats. A major constituent of terrestrial environments are solid particles such as quartz, silt and clay, which have considerable surface areas and which make up the solid-liquid interfaces of the habitat. In previous experiments the adsorption of DNA to chemically purified quartz and clay minerals was shown and the partial protection of adsorbed DNA against DNAase I. In a microcosm consisting of natural groundwater aquifer material (GWA) sampled directly from the environment and groundwater (GW) both linear duplex and supercoiled plasmid DNA molecules bound rapidly and quantitatively to the minerals. The divalent cations required to form the association were those present in the GWA/GW microcosm. The association was stable to extended elution over one week at 23 degrees C. Upon adsorption, the DNA became highly resistant against enzymatic degradation. About 1000 times higher DNAase I concentrations were needed to degrade bound DNA to the same extent as DNA dissolved in GW. Furthermore, chromosomal and plasmid DNA bound on GWA transformed competent cells of Bacillus subtilis. However, in contrast to DNA in solution, on GWA the chromosomal DNA was more active in transformation than the plasmid DNA. The studies also revealed that in the transformation of B. subtilis Mg2+ can be replaced by Na+, K+ or NH4+. The observations suggest that in soil and sediment environments, mineral material with inorganic precipitates and organic matter can harbour extracellular DNA leaving it available for genetic transformation.
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Affiliation(s)
- G Romanowski
- Genetik, Fachbereich Biologie, Universität Oldenburg, Germany
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12
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Romanowski G, Lorenz MG, Sayler G, Wackernagel W. Persistence of Free Plasmid DNA in Soil Monitored by Various Methods, Including a Transformation Assay. Appl Environ Microbiol 1992; 58:3012-9. [PMID: 16348772 PMCID: PMC183041 DOI: 10.1128/aem.58.9.3012-3019.1992] [Citation(s) in RCA: 116] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The persistence and stability of free plasmid pUC8-ISP DNA introduced into 10-g samples of various soils and kept at 23°C were monitored over a period of 60 days. The soils were sampled at a plant science farm and included a loamy sand soil (no. 1), a clay soil (no. 2), and a silty clay soil (no. 3). Four different methods allowed monitoring of (i) the production of acid-soluble radioactive material from [
3
H]thymidine-labeled plasmid DNA, (ii) the decrease of hybridizing nucleotide sequences in slot blot analysis, (iii) the loss of plasmid integrity measured by Southern hybridization, and (iv) the decay of the biological activity as determined by transformation of Ca
2+
-treated
Escherichia coli
cells with the DNA extracted from soil. Acid-soluble material was not produced within the first 24 h but then increased to 45% (soil no. 1), 27% (soil no. 2), and 77% (soil no. 3) until the end of incubation. A quite parallel loss of material giving a slot blot hybridization signal was observed. Southern hybridization indicated that after 1 h in the soils, plasmid DNA was mostly in the form of circular and full-length linear molecules but that, depending on the soil type, after 2 to 5 days full-length plasmid molecules were hardly detectable. The transforming activity of plasmid DNA reextracted from the soils followed inactivation curves over 2 to 4 orders of magnitude and dropped below the detection limit after 10 days. The inactivation was slower in soil no. 2 (28.2-h half-life time of the transforming activity of a plasmid molecule) than in soils no. 3 (15.1 h) and no. 1 (9.1 h). The studies provide data on the persistence of free DNA molecules in natural bacterial soil habitats. The data suggest that plasmid DNA may persist long enough to be available for uptake by competent recipient cells in situ.
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Affiliation(s)
- G Romanowski
- Genetik, Fachbereich Biologie, Universität Oldenburg, Postfach 2503, W-2900 Oldenburg, Germany, and Center for Environmental Biotechnology, University of Tennessee, Knoxville, Tennessee 37932
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13
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Lorenz MG, Gerjets D, Wackernagel W. Release of transforming plasmid and chromosomal DNA from two cultured soil bacteria. Arch Microbiol 1991; 156:319-26. [PMID: 1793338 DOI: 10.1007/bf00263005] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The release of chromosomal and plasmid DNA from Acinetobacter calcoaceticus and Bacillus subtilis cultivated in minimal medium and broth over a period of 50 h was monitored and related to growth phase, autolysis, DNase production and natural competence. The released DNAs were biologically active in natural transformation. In addition, the circular integrity of a released B. subtilis shuttle vector (pHV14) was demonstrated by artificial transformation of Escherichia coli. In cultures of both strains high molecular weight DNA accumulated, particularly during the stationary and death phase (up to 30 micrograms ml-1). Generally, despite the presence in culture fluids of DNase activity (and of an intracellular enzyme, catalase, indicating some cell lysis) there was high transforming activity of chromosomal and plasmid DNA even 40 h after the cultures reached the stationary phase. In cultures of B. subtilis in minimal medium a presumably active release of intact plasmids and chromosomal DNA occurred during the competence phase. The release of biologically functional DNA during essentially all growth phases of a gram-positive and a gram-negative member of soil bacteria might facilitate horizontal gene transfer by transformation in natural habitats.
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Affiliation(s)
- M G Lorenz
- Genetik, Fachbereich Biologie, Universität Oldenburg, Federal Republic of Germany
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14
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Lorenz MG, Wackernagel W. High Frequency of Natural Genetic Transformation of
Pseudomonas stutzeri
in Soil Extract Supplemented with a Carbon/Energy and Phosphorus Source. Appl Environ Microbiol 1991; 57:1246-51. [PMID: 16348463 PMCID: PMC182876 DOI: 10.1128/aem.57.4.1246-1251.1991] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Agar medium (SME) prepared from aqueous soil extract was used to examine genetic transformation of
Pseudomonas stutzeri
JM302 (
his-1
) by homologous
his
+
DNA in a plate transformation assay. Growth studies indicated that SME was strongly limited in carbon and nitrogen sources. Transformation was observed on SME supplemented with pyruvate, phosphate, and ammonium. A 25-fold increase of the transformation frequency was obtained with nitrogen limitation when SME was supplemented with only pyruvate plus phosphate. Similar results were obtained with artificial soil extract medium prepared on the basis of the chemical analysis of the soil extract. On a standard minimal medium, transformation frequencies also increased (10- to 60-fold) when ammonium, phosphate, or pyruvate was growth limiting. Limitation of two or three nutrients did not stimulate transformation. The size of the inoculum (2 × 10
3
to 2 × 10
7
cells) was irrelevant to the enhanced transformation under nitrogen limitation on SME or standard minimal medium. We further show that
P. stutzeri
can use a variety of carbon and energy sources for competence development. It is concluded that genetic transformation of
P. stutzeri
is possible in the chemical environment of soil upon supply of nutrients and may be strongly stimulated by a growth-limiting concentration of single nutrients including sources of C, N, or P.
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Affiliation(s)
- M G Lorenz
- Genetik, Fachbereich Biologie, Postfach 2503, Universität Oldenburg, D-2900 Oldenburg, Federal Republic of Germany
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15
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Lorenz MG, Wackernagel W. Natural genetic transformation of Pseudomonas stutzeri by sand-adsorbed DNA. Arch Microbiol 1990; 154:380-5. [PMID: 2244790 DOI: 10.1007/bf00276535] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In a soil/sediment model system we have shown recently that a gram-positive bacterium with natural competence (Bacillus subtilis) can take up transforming DNA adsorbed to sand minerals. Here we examined whether also a naturally transformable soil bacterium of the gram-negative pseudomonad (Pseudomonas stutzeri) can be transformed by mineral-associated DNA. For these studies the transformation protocol of this species was further improved and characterized. The peak of competence during growth of P. stutzeri was determined to occur at the beginning of the stationary phase. The competence state was conserved during shock freezing and thawing of cells in 10% glycerol. Kinetic experiments showed that transformant formation after addition of DNA to competent cells proceeded for more than 2 h with DNA adsorption to cells being the rate limiting step. By means of the defined protocol P. stutzeri was shown to be transformed by sand-adsorbed DNA. Transformation by adsorbed or dissolved DNA occurred between 16 degrees and 44 degrees C. Efficiency and DNaseI-sensitivity of transformation by DNA adsorbed to sand or in liquid were comparable. It is concluded that uptake of particle-bound DNA by P. stutzeri in soil is possible. This finding adds evidence to the view that transformation occurs in natural environments where DNA is assumed to be significantly associated with mineral/particulate material and thereby is protected against enzymatic degradation.
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Affiliation(s)
- M G Lorenz
- Arbeitsgruppe Genetik, Universität Oldenburg, Federal Republic of Germany
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16
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Doyle RJ, Streips UN, Imada S, Fan VS, Brown WC. Genetic transformation with cell wall-associated deoxyribonucleic acid in Bacillus subtilis. J Bacteriol 1980; 144:957-66. [PMID: 6777372 PMCID: PMC294758 DOI: 10.1128/jb.144.3.957-966.1980] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Cell walls from bacillus subtilis 168 were prepared by conventional methods and found to contain deoxyribonucleic acid (DNA). In transformation assays, after autolysis, it was found that two major regions of the chromosome were selectively enriched in the wall preparations. One region clustered around the replication origin and is represented by the markers purA16, ts8132, thiC5, sacA321, and hisA1. The other region included the replication terminus with representative loci metB10, citK5, gltA292, and pyrA1. All other (internal) loci which were examined showed no statistical enrichment. The two areas of enrichment were similar to but more extensive than those reported for membrane-DNA complexes. The wall preparations also contained protein and lipid, indicating a possible membrane involvement. Analyses of the cell walls revealed that the fatty acid composition of the membrane component was not typical of the for B. subtilis protoplast membranes or for lipoteichoic acids. In addition, radioiodination of cell wall autolysates, followed by gel electrophoresis and autoradiography, demonstrated the presence of proteins not readily detectable in bulk protoplast membranes or on the surfaces of intact cells. These data suggest that a unique component of the membrane and regions of the B. subtilis genome involved in DNA replication events are tightly associated with cell walls. The binding of DNA-membrane complexes to the "rigid" cell wall and the replication of the wall could be a mechanism by which the segregation of growing chromosomes occurs.
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