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  • 1
    Electronic Resource
    Electronic Resource
    Acetobacter xylinum contains several plasmids: Evidence for their involvement in cellulose formation (1983)
    Springer
    Archives of microbiology 134 (1983), S. 9-11 
    Details
    ISSN: 1432-072X
    Keywords: Acetobacter xylinum ; Cellulose ; Plasmids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The cellulose producing bacterium Acetobacter xylinum contains two plasmids of size 44 and 64 kilobases (kb) and presumably small amounts of a 16 kb plasmid. The cells also contain large plasmids of varying molecular weight, the majority being between 200–300 kb in size. Comparison with thirteen non-reverting cellulose-negative (Cel-) mutants indicated that eight of these strains had identifiable changes in their content of plasmid DNA. These changes are difficult to explain at present, but represent sufficient evidence to conclude that relationships between the plasmids and cellulose synthesis may exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00429398
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  • 2
    Electronic Resource
    Electronic Resource
    Complementation of cellulose-negative mutants of Acetobacter xylinum by the cloned structural gene for phosphoglucomutase (1991)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 77 (1991), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Eleven cellulose-negative mutants of Acetobacter xylinum were analysed with respect to the activities of the enzymes known to be involved in cellulose biosynthesis. The analysis showed that all the mutants were deficient in phosphoglucomutase. All 11 mutants were complemented with a recombinant cosmid from a gene bank of wild type A. xylinum DNA. A subcloned 3.8-kb DNA fragment from the cosmid insert expressed high levels of phosphoglucumutase in Escherichia coli. Electrophoretic analysis showed that the introduced A. xylinum activity could be separated from the endogenous phosphoglucomutase present in E. coli. The experiments thus demonstrated that the cloned DNA fragment contained the A. xylinum structural gene for phosphoglucomutase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1991.tb04370.x
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  • 3
    Electronic Resource
    Electronic Resource
    Heterologous gene expression in Lactococcus lactis; expression of the Azotobacter vinelandii algE6 gene product displaying mannuronan C-5 epimerase activity (2003)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 227 (2003), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The Azotobacter vinelandii mannuronan C-5 epimerases AlgE1–7 can be used to improve the properties of the commercially important polysaccharide alginate that is widely used in a variety of products, such as food and pharmaceuticals. Since lactic acid bacteria are generally regarded as safe, they are attractive candidates for production of the epimerases. A. vinelandii genes are GC-rich, in contrast to those of lactic acid bacteria, but we show here that significant expression levels of the epimerase AlgE6 can be obtained in Lactococcus lactis using the nisin-controlled expression system. A 1200-fold induction ratio was obtained resulting in an epimerase activity of 23 900 dpm mg−1 h−1, using a tritiated alginate substrate. The epimerase was detected by Western blotting and nuclear magnetic resonance spectroscopy analysis of its reaction product showed that the enzyme displayed catalytic properties similar to those produced in Escherichia coli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0378-1097(03)00685-2
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  • 4
    Electronic Resource
    Electronic Resource
    The dual roles of AlgG in C-5-epimerization and secretion of alginate polymers in Pseudomonas aeruginosa (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 47 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pseudomonas aeruginosa strains causing chronic pulmonary infections in cystic fibrosis patients produce high levels of alginate, an exopolysaccharide that confers a mucoid phenotype. Alginate is a linear polymer of d -mannuronate (M) and variable amounts of its C-5-epimer, l -guluronate (G). AlgG is a periplasmic C-5-epimerase that converts poly d -mannuronate to the mixed M+G sequence of alginate. To understand better the role and mechanism of AlgG activity, a mutant was constructed in the mucoid strain FRD1 with a defined non-polar deletion of algG . Instead of producing poly mannuronate, the algG deletion mutant secreted dialysable uronic acids, as does a mutant lacking the periplasmic protein AlgK. High levels of unsaturated ends and the nuclear magnetic resonance spectroscopy pattern revealed that the small, secreted uronic acids were the products of extensive polymer digestion by AlgL, a periplasmic alginate lyase co-expressed with AlgG and AlgK. Thus, AlgG is bifunctional with (i) epimerase activity and (ii) a role in protecting alginate from degradation by AlgL during transport through the periplasm. AlgK appears to share the second role. AlgG and AlgK may be part of a periplasmic protein complex, or scaffold, that guides alginate polymers to the outer membrane secretin (AlgE). To characterize the epimerase activity of AlgG further, the algG4 allele of poly mannuronate-producing FRD462 was shown to encode a protein lacking only the epimerase function. The sequence of algG4 has a Ser-272 to Asn substitution in a serine–threonine-rich and conserved region of AlgG, which revealed a critical residue for C-5-epimerase activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03361.x
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  • 5
    Electronic Resource
    Electronic Resource
    A small derivative of the broad-host-range plasmid RK2 which can be switched from a replicating to a non-replicating state as a response to an externally added inducer (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 180 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: TrfA is the only plasmid-encoded protein required for RK2 replication. We report here the construction and characterization of an RK2-based vector in which trfA is expressed from the inducible promoter Pm. The resulting construct, pJBSD1, was found to replicate in Escherichia coli DH5a (recA−) only in the presence of a Pm inducer. In two tested E. coli recA+ strains pJBSD1 could replicate in the absence of inducer, but a replication inducer-dependent phenotype was obtained in these strains by introducing a mutation known to reduce the trfA expression level. The plasmid construct could be used as a conditional suicide vector system for targeted chromosomal integration via homologous recombination. This feature may potentially be used for many types of studies in microbial molecular biology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb08799.x
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular cloning and analysis of a pleiotropic regulatory gene locus from the nystatin producer Streptomyces noursei ATCC11455 (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 177 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A regulatory gene locus from Streptomyces noursei ATCC14455, the producer of the antifungal antibiotic nystatin, was cloned in Streptomyces lividans based on its ability to activate actinorhodin (Act) production in this host. Deletion and DNA sequencing analyses showed that a small gene, designated ssmA, located downstream of an afsR homologue (a known pleiotropic regulator) was responsible for the Act overproduction in S. lividans. Database searches for the ssmA gene product revealed its limited similarity to the AfsR2 regulatory protein from S. lividans and CREA catabolite repressor from Aspergillus nidulans. To study the effect of ssmA on nystatin production, this gene was either deleted from S. noursei genome, or placed under control of PermE* promoter and introduced in S. noursei. The properties of the corresponding strains indicate that ssmA is involved in regulation of growth and antibiotic production only in the media with certain carbon sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb13746.x
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  • 7
    Electronic Resource
    Electronic Resource
    New broad-host-range promoter probe vectors based on the plasmid RK2 replicon (2001)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 195 (2001), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Broad-host-range plasmid RK2-based promoter probe vectors with a known nucleotide sequence were constructed. In the absence of an upstream promoter, the expression of two tested reporter genes (luc and lacZ) in Escherichia coli was virtually zero, while insertion of the Ptrc promoter resulted in strong inducer-dependent expression. The lacZ-based vectors were mobilized into Pseudomonas fluorescens ST, Pseudomonas putida KT2442, Sphingomonas spp. and Burkholderia spp. LB400, and expression analyses indicated that the properties observed in E. coli are maintained across the species barriers. In addition, the previously established knowledge of RK2 molecular biology allows easy manipulations of features such as plasmid copy number, further extending the application potential of the vectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2001.tb10503.x
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  • 8
    Electronic Resource
    Electronic Resource
    A family of modular type mannuronan C-5-epimerase genes controls alginate structure in Azotobacter vinelandii (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 16 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The l-guluronic acid residues in the Azotobacter vinelandii polysaccharide alginate originate from a post-polymerization reaction catalysed by the enzyme mannuronan C-5-epimerase (ME). We have previously reported the cloning and expression of an A. vinelandii gene encoding this enzyme, and we show here that the organism encodes at least four other ME genes originating from a common ancestor gene by a complex rearrangement process. The biological function of the corresponding enzymes is probably to catalyse the formation of alginates with a variety of physical properties. This model may explain the origin of the structural variability found in alginates isolated both from prokaryotic and eukaryotic organisms. The A. vinelandii enzymes may also potentially be useful for certain medical and biotechnological applications of this commercially important polysaccharide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.tb02433.x
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  • 9
    Electronic Resource
    Electronic Resource
    An experimental study on carbon flow in Escherichia coli as a function of kinetic properties and expression levels of the enzyme phosphoglucomutase (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 58 (1998), S. 299-302 
    Details
    ISSN: 0006-3592
    Keywords: phosphoglucomutase ; site-directed mutagenesis ; kinetic constants ; Pm promoter ; metabolic engineering ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mutants of Escherichia coli deficient in phosphoglucomutase accumulate amylose when the cells are grown on maltose or galactose as carbon source. In the presence of physiological levels of phosphoglucomutase, most of the sugar is catabolized, leading to strongly reduced levels of amylose accumulation. By varying the expression level of heterologous phosphoglucomutase, we show that the minimum level needed to block amylose accumulation corresponds to a phosphoglucomutase activity of 150-600 nmole substrate transformed per min per mg of total soluble protein. Mutant phosphoglucomutases with strongly reduced Vmax values and increased Km values for the substrate glucose-1-phosphate or the co-substrate glucose-1,6-diphosphate, could also reduce amylose accumulation, but much higher enzyme expression levels were required. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58:299-302, 1998.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    The plasmids of Acetobacter xylinum and their interaction with the host chromosome (1987)
    Springer
    Molecular genetics and genomics 208 (1987), S. 76-83 
    Details
    ISSN: 1617-4623
    Keywords: Acetobacter xylinum ; Plasmid ; Rearrangement ; Cellulose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Acetobacter xylinum contains a complex system of plasmid DNA molecules. Plasmids of molecular weights or copy numbers different from the original wild-type, are found in different types of mutants. Restriction endonuclease digestion and DNA/DNA hybridization analysis, showed that the plasmids often contained partly, but not completely the same DNA sequences. Two of these plasmid classes were analysed in more detail, and could be shown to differ in size by about 5 kb. Hybridization analysis using cloned DNA fragments as probes, showed that sequences lacking in the smallest plasmid were still present in a DNA fraction co-migrating with linearized chromosomal DNA. In addition, at least part of the DNA in the smallest plasmid was present both in the plasmid and chromosomal DNA fraction. Analysis of a particular strain containing an insertion of transposon Tn1, also indicated the existence of complex interactions between plasmids and chromosomal DNA. Together with experiments on conjugative transfer and curing of the plasmids, the results indicate that at least part of the genetic system of A. xylinum is unusual when compared to that of other genetically characterized bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330425
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