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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 15 (1994), S. 0 
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Molecular methods based on detection of specific DNA sequences are increasingly used to monitor microbial strains and communities in soils. Here, we report that desiccation of soil, a condition that frequently occurs in nature, may contribute considerably to dissimilarity between DNA levels and colony forming units of introduced bacteria. Three types of soil samples were supplemented with Escherichia coli or Alcaligenes eutrophus suspensions and incubated at 30°C in the presence or absence of dehydrating silica gel. Alternatively, seeded soil samples were desiccated by freeze-drying. At regular time points cells and total DNA were extracted and colony forming units and plasmid DNA were determined, respectively. These analyses showed that the decrease of the number of colony forming units was faster in desiccating than in control soil. Both in desiccating and in control soil, plasmid DNA levels were more stable than culturable counts. Long-term incubation experiments showed that in desiccating soil but not in control soil E. coli plasmid DNA remained intact and biologically active for at least 17 days after disappearance of E. coli culturable counts.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 14 (1994), S. 0 
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Conjugal transfer between Escherichia coli and Alcaligenes eutrophus of plasmid pDN705, containing genes encoding resistance against cadmium, zinc, and cobalt (czc genes) occurred in heavy metal polluted soil. The selective pressure from heavy metals (especially Zn2+) resulted in an increased number of resistant transconjugants and higher respiratory activities in sterile soil. As filter mattings showed no or even a negative effect of Zn2+ on plasmid transfer, the increase of the number of transconjugants in polluted was probably due to growth rather than stimulated transfer. High numbers of recipients inhibited extended growth of transconjugants in sterile unpolluted soil. This intranspecific competition was overcome in the presence of heavy metals. In non-sterile soil, such an effect of heavy metals was not always evident, and seemed to be related to the severity of the selective pressure and inversely to the overall biological competition.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Ralstonia metallidurans, formerly known as Alcaligenes eutrophus and thereafter as Ralstonia eutropha, is a β-Proteobacterium colonizing industrial sediments, soils or wastes with a high content of heavy metals. The type strain CH34 carries two large plasmids (pMOL28 and pMOL30) bearing a variety of genes for metal resistance. A chronological overview describes the progress made in the knowledge of the plasmid-borne metal resistance mechanisms, the genetics of R. metallidurans CH34 and its taxonomy, and the applications of this strain in the fields of environmental remediation and microbial ecology. Recently, the sequence draft of the genome of R. metallidurans has become available. This allowed a comparison of these preliminary data with the published genome data of the plant pathogen Ralstonia solanacearum, which harbors a megaplasmid (of 2.1 Mb) carrying some metal resistance genes that are similar to those found in R. metallidurans CH34. In addition, a first inventory of metal resistance genes and operons across these two organisms could be made. This inventory, which partly relied on the use of proteomic approaches, revealed the presence of numerous loci not only on the large plasmids pMOL28 and pMOL30 but also on the chromosome. It suggests that metal-resistant Ralstonia, through evolution, are particularly well adapted to the harsh environments typically created by extreme anthropogenic situations or biotopes.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The czc determinant, which mediates resistance to Co2+, Zn2+ and Cd2+ in Alcaligenes eutrophus CH34 by cation efflux, is regulated by a two-component regulatory system composed of the sensor histidine kinase CzcS and the response activator CzcR (in addition to other components previously described). Regulatory genes are arranged in an upstream regulatory region (URR) and a downstream regulatory region (DRR). Transcription of czcCBA and of the URR was regulated by heavy-metal cations. DNA sequencing of the region downstream of czcD revealed the presence of the czcR and czcS genes which together with czcD form the DRR. Regulation of the DRR was studied with a czcD::lacZ translational fusion and a czcS::lux transcriptional fusion. Expression of both genes is also regulated by heavy metals. The genes of the URR yielded three mRNAs of approx. 1200, 500 and 200 nucleotides, respectively. The genes czcCBA for the cation/proton antiporter CzcCBA were transcribed by one operon as a transcript of 6200 nucleotides.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 14 (1994), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: Retromobilization of the nonconjugative (Tra−Mob+) IncQ vector, pMOL155, and the non-mobilizable (Tra−Mob−) vector, pMOL149, by means of the IncP plasmids RP4 and pULB113 (RP4::Mu3A), was studied in plate matings and in soil microcosms, and compared with direct and triparental mobilization. Both vectors harbour the czc genes, originating from Alcaligenes eutrophus, which code for resistance to Co, Zn, and Cd. The donor of the czc genes was Escherichia coli which did not express these genes. The recipient, Alcaligenes eutrophus, expressed the czc genes very well. Retromobilization, direct and triparental mobilization of pMOL155 was observed in sterile soil. Both the addition of nutrients and heavy metals significantly enhanced the number of (retro)transconjugants. Retromobilization was also detected in nutrient amended nonsterile soil, but the presence of the autochthonous soil biota strongly reduced the number of retrotransconjugants and also prevented their increase upon application of heavy metals to the soil. Retromobilization of the czc genes, cloned in pMOL149, by using pULB113 was also observed, yet only in sterile, nutrient amended, heavy metal polluted soil.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 59 (1989), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The broad-host-range, IncQ, plasmid R300B (Sm, Su) has been stably transferred to two strains of sulphate-reducing bacteria (Desulfovibrio sp. 8301 and Desulfovibrio desulfuricans 8312), using the IncP1 transfer system of the helper plasmid pRK2013 and cocultivation of sulphate-reducing bacteria with facultative anaerobes in media provided with sulphate and nitrate ions as electron acceptors. R300B was transferred at a frequency of 10−2 to 1 per acceptor cell. The SmR marker was expressed in both sulphate-reducing bacteria strains while the SuR was expressed only in strain 8301. R300B can also be transferred back to E. coli strains provided with IncP1 plasmids taking advantage of the retrotransfer ability of these plasmids. This occurs at a frequency up to 10−4 by recipient E. coli cell.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 66 (1990), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Properties of lipases excreted by 4 psychrotropic Moraxella strains from antarctic sea water have investigated. Despite an optimal cell generation time at 25°C, maximal lipase excretion essentially occurs at low temperatures. These enzymes are characterized by a shift of the apparent optimal activity towards low temperatures, by a reduction of the activation energy value and by a decrease in heat stability. These lipases are associated with lipopolysaccharides, forming high molecular weight complexes. One of the selected strain is able to express the antibiotic resistances carried by RP4, at both 4 and 25°C.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The IncP1 type plasmids pULB113 (RP4:: mini-Mu) and pJB3JI were used for chromosome mobilization and R prime formation in Agrobacterium tumefaciens. With pULB113, R primes were selected for complementation of an auxotrophic marker in an Alcaligenes eutrophus recipient strain. With pJB3JI, R primes containing the Agrobacterium chromosomal virulence region chv, inactivated by a Tn5 insertion, were constructed. Selection was for kanamycin resistance in E. coli strain GV1000. Complementation tests were performed in auxotrophic A. tumefaciens, A. eutrophus and Pseudomonas fluorescens strains. This allowed us to map 9 loci, including the chv loci, in a region accounting for about 10% of the Agrobacterium chromosome.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pyoverdin production by Pseudomonas aeruginosa strain 7NSK2 was induced by Zn(II) in the presence of iron. A mutant was isolated in which Zn(II) no longer induced pyoverdin production. The sss gene which was inactivated in this mutant was cloned and sequenced. Its protein sequence showed 50% identity to the XerC protein of Escherichia coli, which is a member of the lambda integrase family of site-specific recombinases. An open reading frame was found upstream of sss whose protein sequence showed strong identity to DapF, the diaminopimelate epimerase. In E. coli, xerC is part of a multicistronic unit that also contains dapF. The sss gene of P. aeruginosa could restore site-specific recombination at cer in an E. coii xerC mutant and the E. coii xerC gene could complement a genomic sss mutation in P. aeruginosa.
    Type of Medium: Electronic Resource
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