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  • 11
    Electronic Resource
    Electronic Resource
    Reversible inactivation of d-xylose utilization by d-glucose in the pentose-fermenting yeast Pachysolen tannophilus (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 92 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A major problem in fermenting pentoses using lignocellulosic substrates is the presence of d-glucose which inhibits d-xylose utilization. We previously showed that d-glucose represses the induction of xylose reductase and xylitol dehydrogenase activities, thereby inhibiting d-xylose utilization in Pachysolen tannophilus. The question arose whether d-glucose can also inactivate d-xylose fermentation. P. tannophilus cells were grown on a defined d-xylose-containing liquid medium. At about 40 h, d-glucose was added to a final concentration of 3% (w/v). This led to a rapid cessation of d-xylose utilization, which resumed after 10–12 h before d-glucose was completely consumed. This suggests that d-glucose inactivated existing d-xylose catabolic enzymes and that inactivation was reversed at low d-glucose concentrations. This reversible inactivation was distinct from d-glucose repression. Addition of cycloheximide did not block the resumption of d-xylose consumption, suggesting that reactivation was independent of protein synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb05224.x
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  • 12
    Electronic Resource
    Electronic Resource
    Site-directed mutagenesis of the cysteine residues in the Pichia stipitis xylose reductase (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 147 (1997), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Xylose reductase catalyzes the reduction of xylose to xylitol and is known to play a pivotal role in pentose metabolism in yeasts. We previously showed that a cysteine residue may be involved in binding of the coenzyme NADPH to the Pichia stipitis xylose reductase through chemical modification studies. The question arose as to which of the three cysteine residues in this enzyme may be involved in coenzyme binding. We cloned the XYL1 gene encoding xylose reductase from P. stipitis into the phagemid pEMBL18(+) suitable for site-directed mutagenesis. Each of the three cysteine residues (Cys19, Cys27 and Cys130) was individually mutated to serine. All three Cys→Ser variants remained functional, but with reduced catalytic activity. Sensitivity of the P. stipitis xylose reductase to thiol-specific reagents was attributed to both Cys27 and Cys130 residues as substitution of either residue with Ser resulted in a significant but incomplete loss of sensitivity to PCMBS. The apparent Km values of the Cys variants for NADPH, NADH and xylose did not differ from those of the wild-type enzyme isolated from yeast by more than 4-fold. Our results suggest that none of the Cys residues are directly involved in NADPH binding, although Cys130 may reside in or near the coenzyme binding region and might play a role in coenzyme specificity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1997.tb10246.x
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  • 13
    Electronic Resource
    Electronic Resource
    Effects of 2,2′,5,5′-tetrachlorobiphenyl and biphenyl on cell membranes of Ralstonia eutropha H850 (2001)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 200 (2001), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of 2,2′,5,5′-tetrachlorobiphenyl (TeCB), a PCB congener, and biphenyl on the cytoplasmic membranes of Ralstonia eutropha H850 were investigated by measuring fluorescence polarization using 1,6-diphenyl-1,3,5-hexatriene (DPH) as the probe, and determining the cellular fatty acid compositions. TeCB significantly affected the membrane of R. eutropha H850 cells grown on fructose by decreasing DPH fluorescence polarization. In contrast, the membrane of cells grown on biphenyl showed a considerably less significant effect of TeCB on membrane polarization than in fructose-grown cells. An increase in the ratio of total saturated to unsaturated fatty acids in cells grown on biphenyl suggested less of a fluidizing effect of TeCB on membranes in those cells. When biphenyl-grown cells were transferred back to a fructose medium, they required 25 generations for the membrane polarization and fatty acid compositions of these cells to revert back to those of the initial fructose-grown cells. The re-adaptation to a change in temperature required only five generations to return to normal. These results show that biphenyl affects cells in more ways than simply fluidizing the cytoplasmic membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2001.tb10686.x
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  • 14
    Electronic Resource
    Electronic Resource
    Identification of lysine-78 as an essential residue in the Saccharomyces cerevisiae xylose reductase (2002)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 209 (2002), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Yeast xylose reductases are hypothesized as hybrid enzymes as their primary sequences contain elements of both the aldo–keto reductases (AKR) and short chain dehydrogenase/reductase (SDR) enzyme families. During catalysis by members of both enzyme families, an essential Lys residue H-bonds to a Tyr residue that donates proton to the aldehyde substrate. In the Saccharomyces cerevisiae xylose reductase, Tyr49 has been identified as the proton donor. However, the primary sequence of the enzyme contains two Lys residues, Lys53 and Lys78, corresponding to the conserved motifs for SDR and AKR enzyme families, respectively, that may H-bond to Tyr49. We used site-directed mutagenesis to substitute each of these Lys residues with Met. The activity of the K53M variant was slightly decreased as compared to the wild-type, while that of the K78M variant was negligible. The results suggest that Lys78 is the essential residue that H-bonds to Tyr49 during catalysis and indicate that the active site residues of yeast xylose reductases match those of the AKR, rather than SDR, enzymes. Intrinsic enzyme fluorescence spectroscopic analysis suggests that Lys78 may also contribute to the efficient binding of NADPH to the enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2002.tb11135.x
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  • 15
    Electronic Resource
    Electronic Resource
    The role of the Sphingomonas species UG30 pentachlorophenol-4-monooxygenase in p-nitrophenol degradation (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 173 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Pentachlorophenol-4-monooxygenase is an aromatic flavoprotein monooxygenase which hydroxylates pentachlorophenol and a wide range of polyhalogenated phenols at their para position. The PCP-degrading Sphingomonas species UG30 was recently shown to mineralize p-nitrophenol. In this study, the UG30 pcpB gene encoding the pentachlorophenol-4-monooxygenase gene was cloned for use to study its potential role in p-nitrophenol degradation. The UG30 pcpB gene consists of 1614 bp with a predicted translational product of 538 amino acids and a molecular mass of 59 933 Da. The primary sequence of pentachlorophenol-4-monooxygenase contained a highly conserved FAD binding site at its N-terminus associated with a βαβ fold. UG30 has been shown previously to convert p-nitrophenol to 4-nitrocatechol. We observed that pentachlorophenol-4-monooxygenase catalyzed the hydroxylation of 4-nitrocatechol to 1,2,4-benzenetriol. About 31.2% of the nitro substituent of 4-nitrocatechol (initial concentration of 200 μM) was cleaved to yield nitrite over 2 h, indicating that the enzyme may be involved in the second step of p-nitrophenol degradation. The enzyme also hydroxylated p-nitrophenol at the para position, but only to a very slight extent. Our results confirm that pentachlorophenol-4-monooxygenase is not the primary enzyme in the initial step of p-nitrophenol metabolism by UG30. The UG30 pcpB sequence has been deposited at the GenBank under accession number AF059680.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb13509.x
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  • 16
    Electronic Resource
    Electronic Resource
    Mutational analysis of the role of the conserved lysine-270 in the Pichia stipitis xylose reductase (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 159 (1998), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Xylose reductase catalyzes the NAD(P)H-dependent reduction of xylose to xylitol and is essential for growth on xylose by yeasts. To understand the nature of coenzyme binding to the Pichia stipitis xylose reductase, we investigated the role of the strictly conserved Lys270 in the putative IPKS coenzyme binding motif by site-directed mutagenesis. The Lys270Met variant exhibited lower enzyme activity than the wild-type enzyme. The apparent affinity of the variant for NADPH was decreased 5–16-fold, depending on the substrate used, while the apparent affinity for NADH, measured using glyceraldehyde as the substrate, remained unchanged. This resulted in 4.3-fold higher affinity for NADH over NADPH using glyceraldehyde as the substrate. The variant also showed a 14-fold decrease in Km for xylose, but only small changes were observed in Km values for glyceraldehyde. The wild-type enzyme, but not the Lys270Met variant, was susceptible to modification by the Lys-specific pyridoxal 5′-phosphate. Results of our chemical modification and site-directed mutagenesis study indicated that Lys270 is involved in both NADPH and d-xylose binding in the P. stipitis xylose reductase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1998.tb12848.x
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  • 17
    Electronic Resource
    Electronic Resource
    Green fluorescent protein as a visual marker in a p-nitrophenol degrading Moraxella sp. (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 164 (1998), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The green fluorescent protein gene (gfp) was introduced into a p-nitrophenol-metabolizing strain of Moraxella sp. by chromosomal integration. The gfp-marked transformants, designated Moraxella sp. strains G21 and G25, exhibited green fluorescence under UV light. Molecular characterization by PCR and Southern hybridization showed the presence of gfp in both transformants. Both transformants and the parent strain degraded 720 μM of p-nitrophenol with nitrite release within 4 h after inoculation in minimal medium supplemented with yeast extract. Transformants degraded up to 1440 μM p-nitrophenol and mineralized about 60% of 720 μM p-nitrophenol, both in broth and in soil, to the same extent as the parent strain. Insertion of gfp did not adversely affect the expression of p-nitrophenol-degrading genes in the transformants. Survival studies indicated that individual green fluorescent colonies of transformants can be detected up to 2 weeks after inoculation in soil. These marked strains could be of value in studies on microbial survival in the environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1998.tb13084.x
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  • 18
    Electronic Resource
    Electronic Resource
    Mineralization of p-nitrophenol by pentachlorophenol-degrading Sphingomonas spp. (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 155 (1997), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Pentachlorophenol-degrading Sphingomonas sp. UG30 and Sphingomonas chlorophenolica strains RA2 and ATCC 39723 can transform p-nitrophenol in either mineral salts-glutamate or mineral salts-glucose medium after an initial lag period. However, mineralization of p-nitrophenol by these bacterial strains was observed only in mineral salts-glucose medium. When p-nitrophenol was the sole nitrogen source in the growth medium, UG30 mineralized 32% of 140 mM [14C]p-nitrophenol which was 10% higher than the amount of [14C]p-nitrophenol mineralized in mineral salts-glucose medium. UG30 did not transform or mineralize p-nitrophenol (in a growth medium) in the absence of glucose or glutamate. All three strains released nitrite during p-nitrophenol degradation in mineral salts-glucose medium and mineral salts-glutamate medium. The transformation rate of p-nitrophenol by UG30 was dependent on the initial p-nitrophenol concentration, with the optimal rate being found at 310 μM of p-nitrophenol and inhibition observed at ≥1100 μM of p-nitrophenol. Pre-exposure of UG30 cells to p-nitrophenol eliminated the initial lag phase of p-nitrophenol transformation. However, pre-growth of UG30 cells on pentachlorophenol did not reduce the lag period for p-nitrophenol transformation. Both p-nitrophenol- and pentachlorophenol-induced UG30 cells degraded pentachlorophenol without any lag phase. Thin layer chromatographic analysis of the reaction mixture suggested 4-nitrocatechol was an intermediate of p-nitrophenol transformation by UG30.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1997.tb12693.x
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  • 19
    Electronic Resource
    Electronic Resource
    Survival of κ-carrageenan-encapsulated and unencapsulated Pseudomonas aeruginosa UG2Lr cells in forest soil monitored by polymerase chain reaction and spread plating (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 16 (1995), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A method was developed for direct extraction, purification and amplification of DNA from forest soil. Eighty-two % of the DNA in Pseudomonas aeruginosa UG2Lr introduced into soil was recovered. The detection limit for the strain was approximately 800 cfu g−1 of dry soil based on the polymerase chain reaction (PCR). Survival of κ-carrageenan-encapsulated and unencapsulated UG2Lr was monitored by antibiotic selective and bioluminescence-based nonselective plating and PCR-amplification of a tnsA fragment. After freeze-thaw treatment of soil samples, the unencapsulated UG2Lr declined from an initial population density of 1 × 109 cfu g−1 of dry soil to below the detection threshold of both selective (14 cfu g−1 of dry soil) and nonselective (1 × 103 cfu g−1 of dry soil) plating. However, presence of nonculturable UG2Lr cells in the soil was revealed by PCR and resuscitation of the bacteria. Population density of the encapsulated UG2Lr increased from 2.7 × 106 to 2.9 × 108 cfu g−1 of dry soil after a 3-week incubation at 22°C and declined to 6.3 × 106 cfu g−1 of dry soil after the freeze-thaw treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1995.tb00270.x
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  • 20
    Electronic Resource
    Electronic Resource
    Effect of addition of rhamnolipid biosurfactants or rhamnolipid-producing Pseudomonas aeruginosa on phenanthrene mineralization in soil slurries (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 17 (1995), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: The effect of Pseudomonas aeruginosa UG2 biosurfactants or UG2 inocula on phenanthrene mineralization in uninoculated nonsterile soil slurries and slurries inoculated with the phenanthrene-mineralizing Pseudomonas sp. UG14r was investigated. In sandy loam and silt loam slurries amended with phenanthrene, inoculation with UG14r alone or in co-culture with UG2Lr reduced the lag period before onset of phenanthrene mineralization by 1 week. The total amount mineralized after 5 weeks was lower or not significantly different from the uninoculated control slurries. Inoculation with P. aeruginosa UG2Lr alone did not improve phenanthrene mineralization. In creosote-contaminated soil slurries, no lag period in phenanthrene mineralization was observed in any treatment. After 4 weeks, the greatest extent of mineralization was observed in creosote-contaminated soil slurries inoculated with the UG14r-UG2Lr co-culture and UG14r alone. In sandy loam and silt loam soil slurries inoculated with Pseudomonas sp. UG14r, addition of UG2 rhamnolipid biosurfactants (100 to 400 mg rhamnose equivalents (RE) · l−1 slurry) inhibited phenanthrene mineralization by 10 to 15%. Mineralization was also inhibited in uninoculated sandy loam slurries. In creosote-contaminated soil slurries inoculated with Pseudomonas sp. UG14r, biosurfactants at 250 mg RE · l−1 slurry enhanced mineralization whereas 400 mg RE · l−1 had no effect, compared to unamended slurries. In uninoculated creosote-contaminated soil slurries, UG2 biosurfactants at 250 and 400 mg RE · l−1 slurry enhanced mineralization, compared to unamended slurries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1995.tb00123.x
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