The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Thomas W. Jeffries - One of the best experts on this subject based on the ideXlab platform.
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Xylitol production from DEO hydrolysate of corn stover by Pichia Stipitis YS-30
Journal of Industrial Microbiology & Biotechnology, 2011Co-Authors: Rita C. L. B. Rodrigues, William R. Kenealy, Thomas W. JeffriesAbstract:Corn stover that had been treated with vapor-phase diethyl oxalate released a mixture of mono- and oligosaccharides consisting mainly of xylose and glucose. Following overliming and neutralization, a d -xylulokinase mutant of Pichia Stipitis, FPL-YS30 ( xyl3 -∆1), converted the stover hydrolysate into xylitol. This research examined the effects of phosphoric or gluconic acids used for neutralization and urea or ammonium sulfate used as nitrogen sources. Phosphoric acid improved color and removal of phenolic compounds. d -Gluconic acid enhanced cell growth. Ammonium sulfate increased cell yield and maximum specific cell growth rate independently of the acid used for neutralization. The highest xylitol yield (0.61 g_xylitol/g_xylose) and volumetric productivity (0.18 g_xylitol/g_xylose l) were obtained in hydrolysate neutralized with phosphoric acid. However, when urea was the nitrogen source the cell yield was less than half of that obtained with ammonium sulfate.
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Pichia Stipitis genomics, transcriptomics, and gene clusters.
FEMS yeast research, 2009Co-Authors: Thomas W. Jeffries, Jennifer R. Headman Van VleetAbstract:Genome sequencing and subsequent global gene expression studies have advanced our understanding of the lignocellulose-fermenting yeast Pichia Stipitis. These studies have provided an insight into its central carbon metabolism, and analysis of its genome has revealed numerous functional gene clusters and tandem repeats. Specialized physiological traits are often the result of several gene products acting together. When coinheritance is necessary for the overall physiological function, recombination and selection favor colocation of these genes in a cluster. These are particularly evident in strongly conserved and idiomatic traits. In some cases, the functional clusters consist of multiple gene families. Phylogenetic analyses of the members in each family show that once formed, functional clusters undergo duplication and differentiation. Genome-wide expression analysis reveals that regulatory patterns of clusters are similar after they have duplicated and that the expression profiles evolve along with functional differentiation of the clusters. Orthologous gene families appear to arise through tandem gene duplication, followed by differentiation in the regulatory and coding regions of the gene. Genome-wide expression analysis combined with cross-species comparisons of functional gene clusters should reveal many more aspects of eukaryotic physiology.
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Genomic sequence of the xylose fermenting, insect-inhabiting yeast, Pichia Stipitis
Lawrence Berkeley National Laboratory, 2007Co-Authors: Thomas W. Jeffries, Igor V Grigoriev, Jane Grimwood, José M Laplaza, Andrea Aerts, Asaf Salamov, Jeremy Schmutz, Erika Lindquist, Paramvir Dehal, Harris ShapiroAbstract:Xylose is a major constituent of angiosperm lignocellulose, so its fermentation is important for bioconversion to fuels and chemicals. Pichia Stipitis is the best-studied native xylose fermenting yeast. Genes from P. Stipitis have been used to engineer xylose metabolism in Saccharomycescerevisiae, and the regulation of the P. Stipitis genome offers insights into the mechanisms of xylose metabolism in yeasts. We have sequenced, assembled and finished the genome of P.Stipitis. As such, it is one of only a handful of completely finished eukaryotic organisms undergoing analysis and manual curation. The sequence has revealed aspects of genome organization, numerous genes for biocoversion, preliminary insights into regulation of central metabolic pathways, numerous examples of co-localized genes with related functions, and evidence of how P. Stipitis manages to achieve redox balance while growing on xylose under microaerobic conditions.
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Genome sequence of the lignocellulose-bioconverting and xylose-fermenting yeast Pichia Stipitis
Nature Biotechnology, 2007Co-Authors: Thomas W. Jeffries, Igor V Grigoriev, Jane Grimwood, José M Laplaza, Andrea Aerts, Asaf Salamov, Jeremy Schmutz, Erika Lindquist, Paramvir Dehal, Harris ShapiroAbstract:Xylose is a major constituent of plant lignocellulose, and its fermentation is important for the bioconversion of plant biomass to fuels and chemicals. Pichia Stipitis is a well-studied, native xylose-fermenting yeast. The mechanism and regulation of xylose metabolism in P. Stipitis have been characterized and genes from P. Stipitis have been used to engineer xylose metabolism in Saccharomyces cerevisiae . We have sequenced and assembled the complete genome of P. Stipitis . The sequence data have revealed unusual aspects of genome organization, numerous genes for bioconversion, a preliminary insight into regulation of central metabolic pathways and several examples of colocalized genes with related functions. The genome sequence provides insight into how P. Stipitis regulates its redox balance while very efficiently fermenting xylose under microaerobic conditions.
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The effect of initial cell concentration on xylose fermentation by Pichia Stipitis
Applied Biochemistry and Biotecnology, 2007Co-Authors: Frank K. Agbogbo, Kevin S. Wenger, Guillermo Coward-kelly, Mads Torry-smith, Thomas W. JeffriesAbstract:Xylose was fermented using Pichia Stipitis CBS 6054 at different initial cell concentrations. A high initial cell concentration increased the rate of xylose utilization, ethanol formation, and the ethanol yield. The highest ethanol concentration of 41.0 g/L and a yield of 0.38 g/g was obtained using an initial cell concentration of 6.5 g/L. Even though more xylitol was produced when the initial cell concentrations were high, cell density had no effect on the final ethanol yield. A two-parameter mathematical model was used to predict the cell population dynamics at the different initial cell concentrations. The model parameters, a and b correlate with the initial cell concentrations used with an R 2 of 0.99.
W. H. Van Zyl - One of the best experts on this subject based on the ideXlab platform.
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Differential expression of the Trichoderma reesei β-xylanase II (xyn2) gene in the xylose-fermenting yeast Pichia Stipitis
Applied microbiology and biotechnology, 2001Co-Authors: R. Den Haan, W. H. Van ZylAbstract:The transcriptional control of two native promoters and one heterologous promoter and the production of a heterologous protein from these promoters were evaluated in the xylose-fermenting yeast Pichia Stipitis cultivated on xylose and glucose as carbon sources, using the β-xylanase II xyn2 gene of Trichoderma reesei. The xyn2 gene open reading frame was fused to the P. Stipitis xylose reductase gene (XYL1) promoter, the P. Stipitis transketolase gene (TKL) promoter and the Saccharomyces cerevisiae phosphoglycerate kinase gene (PGK1) promoter DNA sequences on episomal plasmids. The plasmids were transformed into Pichia Stipitis and gene expression and β-xylanase production monitored. The XYL1 promoter was shown to be inducible in the presence of xylose, as xyn2 transcription and β-xylanase activity could be measured when the recombinant strain was cultivated on xylose but not when it was cultivated on glucose. TKL promoter expression was found to be constitutive when either glucose or xylose was used as sole carbon source. The PGK1 promoter did not promote xyn2 transcription in P. Stipitis. The molecular size of the recombinant Xyn2 protein produced by P. Stipitis was 20.7 kDa, which is similar to that of the native T. reesei Xyn2 protein. This indicates no or minimal glycosylation of the recombinant protein. The recombinant xyn2-expressing strain also yielded twice the amount of biomass yielded by the control strain when cultivated in medium containing 1% birchwood xylan as sole carbon source.
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Xylitol production by recombinant Saccharomyces cerevisiae expressing the Pichia Stipitis and Candida shehatae XYL1 genes.
Applied microbiology and biotechnology, 2001Co-Authors: Roshini Govinden, Balakrishna Pillay, W. H. Van Zyl, Dorsamy PillayAbstract:The xylose reductase gene (XYL1) was isolated from Pichia Stipitis and Candida shehatae, cloned into YEp-based vectors under the control of ADH2 and PGK1 promoter/terminator cassettes and introduced into Saccharomyces cerevisiae Y294 by electroporation. Shake-flask fermentations were carried out with 5% xylose and 1% galactose, glucose or maltose as co-substrates. Xylose uptake was similar in both the recombinant strains when different co-substrates were used and slowed once the co-substrate was depleted. The recombinant strains converted xylose to xylitol with yields approaching the theoretical maxima. Xylitol production was most rapid when the co-substrate was still present. Approximately 50% of the xylose was not metabolized due to the depletion of the co-substrate.
Dorsamy Pillay - One of the best experts on this subject based on the ideXlab platform.
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Xylitol production by recombinant Saccharomyces cerevisiae expressing the Pichia Stipitis and Candida shehatae XYL1 genes.
Applied microbiology and biotechnology, 2001Co-Authors: Roshini Govinden, Balakrishna Pillay, W. H. Van Zyl, Dorsamy PillayAbstract:The xylose reductase gene (XYL1) was isolated from Pichia Stipitis and Candida shehatae, cloned into YEp-based vectors under the control of ADH2 and PGK1 promoter/terminator cassettes and introduced into Saccharomyces cerevisiae Y294 by electroporation. Shake-flask fermentations were carried out with 5% xylose and 1% galactose, glucose or maltose as co-substrates. Xylose uptake was similar in both the recombinant strains when different co-substrates were used and slowed once the co-substrate was depleted. The recombinant strains converted xylose to xylitol with yields approaching the theoretical maxima. Xylitol production was most rapid when the co-substrate was still present. Approximately 50% of the xylose was not metabolized due to the depletion of the co-substrate.
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Genomic comparisons among parental and fusant strains of Candida shehatae and Pichia Stipitis.
Current Genetics, 1993Co-Authors: Ephraim T. Selebano, Roshini Govinden, Dorsamy Pillay, Balakrishna Pillay, Abindra S. GuptharAbstract:DNA-DNA binding experiments on selected fusants of Candida shehatae and Pichia Stipitis showed that the nucleus of these strains was composed predominantly of Pichia DNA. Electrophoretic karyotyping revealed that the fusants contained four chromosomes, similar to those found in the Pichia parental strain. In addition, the fusants showed only marginal increases in cell DNA content when compared with the parents. Karyogamy was confirmed, however, by the isolation of recombinant phenotypic segregants, induced by meiotic and mitotic segregation. The results suggest that the fusion led to integration of Candida genes, rather than whole chromosomes, with the entire genome of P. Stipitis.
Meltem Ozcan - One of the best experts on this subject based on the ideXlab platform.
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Characterization of β-xylosidase enzyme from a Pichia Stipitis mutant☆
Bioresource technology, 2007Co-Authors: Pervin Basaran, Meltem OzcanAbstract:beta-Xylosidase production was maximal for the mutant Pichia Stipitis NP54376 grown on xylan as the sole carbon source. beta-Xylosidase was purified from culture supernatant by (NH(4))(2)SO(4) precipitation and a hydrophobic interaction chromatography on phenyl sepharose. Optima of pH and temperature were 5.0 and 50 degrees C, respectively. The enzyme was inhibited by 2-mercaptoethanol (100%) and Fe(3+) (80%), and moderately affected by Cu(2+), Ag(+), NH(4)(+) and Mg(2+) and SDS. The purified xylosidase hydrolyzed xylobiose and xylo-oligosaccharides and it did not exhibit activity against cellulose, starch, maltose and cellobiose. 2.5 g l(-1) glucose repressed beta-xylosidase activity in the NP54376 strain. The K(m) and V(max) values on p-nitrophenyl-beta-xylopyranoside were 1.6 mM and 186 micromol p-nitrophenyl min(-1)mg(-1) protein, respectively. Analysis of the hydrolysis products by HPLC indicated that the major hydrolysis product is xylobiose in all the carbon sources tested.
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Characterization of β-xylosidase enzyme from a Pichia Stipitis mutant☆
Bioresource technology, 2007Co-Authors: Pervin Basaran, Meltem OzcanAbstract:Abstract β-Xylosidase production was maximal for the mutant Pichia Stipitis NP54376 grown on xylan as the sole carbon source. β-Xylosidase was purified from culture supernatant by (NH 4 ) 2 SO 4 precipitation and a hydrophobic interaction chromatography on phenyl sepharose. Optima of pH and temperature were 5.0 and 50 °C, respectively. The enzyme was inhibited by 2-mercaptoethanol (100%) and Fe 3+ (80%), and moderately affected by Cu 2+ , Ag + , NH 4 + and Mg 2+ and SDS. The purified xylosidase hydrolyzed xylobiose and xylo-oligosaccharides and it did not exhibit activity against cellulose, starch, maltose and cellobiose. 2.5 g l −1 glucose repressed β-xylosidase activity in the NP54376 strain. The K m and V max values on p -nitrophenyl-β-xylopyranoside were 1.6 mM and 186 μmol p -nitrophenyl min −1 mg −1 protein, respectively. Analysis of the hydrolysis products by HPLC indicated that the major hydrolysis product is xylobiose in all the carbon sources tested.
Michael Ciciary - One of the best experts on this subject based on the ideXlab platform.
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Xylan-hydrolysing enzymes of the yeast Pichia Stipitis
Applied Microbiology and Biotechnology, 1991Co-Authors: Sabire Özcan, Peter Kötter, Michael CiciaryAbstract:Two xylanolytic enzymes, xylanase and β-xylosidase from the yeast Pichia Stipitis were purified to homogeneity and characterized. Both enzymes are secreted into the culture medium upon growth on xylan. The xylanase is a glycoprotein with an approximate molecular mass of 43 kDa. The N-linked carbohydrate content was estimated to be 26% by endoglycosidase H digestion. The β-xylosidase protein has a molecular mass of 37 kDa as determined by sodium dodecyl sulphate gel electrophoresis. Synthesis of xylanase was found to be inducible by xylan and repressible by xylose and glucose. By contrast, β-xylosidase is synthesized constitutively to a considerable degree. The purified β-xylosidase is able to hydrolyse aryl-β-D-glucosides with an even higher rate than β-xylosides. Thus, this enzyme may not be a specific component of the xylan-degrading system of P. Stipitis.