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The delta1-desturase gene was silenced in order to determine if RNA interference (RNAi) by double-stranded RNA occurs in Mortierella alpina IS-4. Thus RNAi occurs in M. alpina and could be used to alter the types and relative amounts of fatty acids produced by commercial strains of this fungus without mutagenesis or other permanent changes in the genetic background of the producing strains.

Oil-producing fungusMortierella alpina1S-4 is an industrial strain. To determine its physiological properties and to clarify the biosynthetic pathways for polyunsaturated fatty acids, a transformation system for this fungus was established using a derivative of it, i.e., aura5- mutant lacking orotate phosphoribosyl transferase (OPRTase, EC.2.4.2.10) activity. Transformation with a vector containing the homologousura5gene as a marker was successfully performed using microprojectile bombardment, other methods frequently used for transformation, such as the protoplasting, lithium acetate, or electroporation methods, not giving satisfactory results. As a result, two types of transformants were obtained: a few stable transformants overexpressing theura5gene, and many unstable transformants showing OPRTase activity comparable to that of the wild-type strain. The results of quantitative PCR indicated that the stable transformants could retain theura5genes originating from the transformation vector regardless of the culture conditions. On the other hand, unstable transformants easily lost the marker gene under uracil-containing conditions, as expected. In this paper, we report that an overall transformation system for this fungus was successfully established, and propose how to select useful transformants as experimental and industrial strains. [ABSTRACT FROM AUTHOR]

Describes the cloning and sequencing of the ura3 and ura5 genes, and the isolation and characterization of uracil auxotrophs of the fungus Mortierella alpina 1S-4.

The α-glucosidase of Bacillus sp. strain SAM1606 is a member of glycosyl hydrolase family 13, and shows an extraordinarily broad substrate specificity and is one of very few α-glucosidases that can efficiently hydrolyze the α-1,1-glucosidic linkage of α,α′-trehalose (trehalose). Phylogenetic analysis of family-13 enzymes suggests that SAM1606 α-glucosidase may be evolutionally derived from an α-1,6-specific ancestor, oligo-1,6-glucosidase (O16G). Indeed, replacement of Pro273* and Thr342* of B. cereus O16G by glycine and asparagine (the corresponding residues in the SAM1606 enzyme), respectively, was found to cause 192-fold enhancement of the relative catalytic efficiency for trehalose, suggesting that O16G may easily “evolved” into an enzyme with an extended substrate specificity by substitution of a limited number of amino acids, including that at position 273* (an asterisk indicates the amino-acid numbering of the SAM1606 sequence). To probe the role of the amino acid at position 273* of α-glucosidase in determination of the substrate specificity, the amino acid at position 273 of SAM1606 α-glucosidase was replaced by all other naturally occurring amino acids, and the resultant mutants were kinetically characterized. The results showed that substitution of bulky residues (e.g., isoleucine and methionine) for glycine at this position resulted in large increases in the Km values for trehalose and maltose, whereas the affinity to isomaltose was only minimally affected by such an amino-acid substitution at this position. Three-dimensional structural models of the enzyme-substrate complexes of the wild-type and mutant SAM1606 α-glucosidases were built to explore the mechanism responsible for these observations. It is proposed that substitution by glycine at position 273* could eliminate steric hindrance around subsite +1 that originally occurred in parental O16G and is, at least in part, responsible for the acquired broad substrate specificity of SAM1606 α-glucosidase. [ABSTRACT FROM PUBLISHER]

An oleaginous fungus, Mortierella alpina 1S-4, is used commercially for arachidonic acid production. £12-Desaturase, which desaturates oleic acid (18:1n-9) to linoleic acid (18:2n-6), is a key enzyme in the arachidonic acid biosynthetic pathway. To determine if RNA interference (RNAi) by double-stranded RNA occurs in M. alpina 1S-4, we silenced the £12-desaturase gene. The silenced strains accumulate 18:2n-9, 20:2n-9, and Mead acid (20:3n-9), which are not detected in either the control strain or wild type strain 1S-4. The fatty acid composition of stable transformants was similar to that of £12-desaturation-defective mutants previously identified. Thus, RNAi occurs in M. alpina and could be used to alter the types and relative amounts of fatty acids produced by commercial strains of this fungus without mutagenesis or other permanent changes in the genetic background of the producing strains. [ABSTRACT FROM AUTHOR]

Background: Bioethanol produced by the yeast Saccharomyces cerevisiae is currently one of the most promising alternatives to conventional transport fuels. Lignocellulosic hemicelluloses obtained after hydrothermal pretreatment are important feedstock for bioethanol production. However, hemicellulosic materials cannot be directly fermented by yeast: xylan backbone of hemicelluloses must first be hydrolyzed by heterologous hemicellulases to release xylose, and the yeast must then ferment xylose in the presence of fermentation inhibitors generated during the pretreatment., Results: A GIN11/FRT-based multiple-gene integration system was developed for introducing multiple functions into the recombinant S. cerevisiae strains engineered with the xylose metabolic pathway. Antibiotic markers were efficiently recycled by a novel counter selection strategy using galactose-induced expression of both FLP recombinase gene and GIN11 flanked by FLP recombinase recognition target (FRT) sequences. Nine genes were functionally expressed in an industrial diploid strain of S. cerevisiae: endoxylanase gene from Trichoderma reesei, xylosidase gene from Aspergillus oryzae, β-glucosidase gene from Aspergillus aculeatus, xylose reductase and xylitol dehydrogenase genes from Scheffersomyces stipitis, and XKS1, TAL1, FDH1 and ADH1 variant from S. cerevisiae. The genes were introduced using the homozygous integration system and afforded hemicellulolytic, xylose-assimilating and inhibitor-tolerant abilities to the strain. The engineered yeast strain demonstrated 2.7-fold higher ethanol titer from hemicellulosic material than a xylose-assimilating yeast strain. Furthermore, hemicellulolytic enzymes displayed on the yeast cell surface hydrolyzed hemicelluloses that were not hydrolyzed by a commercial enzyme, leading to increased sugar utilization for improved ethanol production., Conclusions: The multifunctional yeast strain, developed using a GIN11/FRT-based marker recycling system, achieved direct conversion of hemicellulosic biomass to ethanol without the addition of exogenous hemicellulolytic enzymes. No detoxification processes were required. The multiple-gene integration technique is a powerful approach for introducing and improving the biomass fermentation ability of industrial diploid S. cerevisiae strains.

It was found that commercial cellulase preparations from Trichoderma viride showed transglucosylation activity toward (+)-catechin and (-)-epigallocatechin gallate (EGCG) using dextrin as a glucosyl donor. To isolate the enzyme exhibiting transglucosylation activity toward (+)-catechin and EGCG, the present study isolated the cDNA encoding the T. viride JCM22452 alpha-amylase homologue (TRa2), which showed high amino acid sequence identity to functionally uncharacterized alpha-amylase homologues from other ascomycetes, which also produced some (+)-catechin and EGCG glucosides. TRa2 was able to glucosylate a wide range of natural flavonoids, particularly (+)-catechin and EGCG, and to hydrolyze maltooligosaccharides (k(cat)/K(m) for maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose were 1.98, 45.2, 58.3, 97.4, and 92.6 s(-1) mM(-1), respectively) except maltose but could not transfer the monoglucosyl residue to maltooligosaccharides. By (1)H NMR and (13)C NMR, the structures of several novel glucosides obtained by commercial cellulase preparations from T. viride and TRa2 were determined as (+)-catechin 5-O-alpha-D-glucopyranoside, (+)-catechin 5-O-alpha-D-maltoside, (+)-catechin 4'-O-alpha-D-maltoside, EGCG 5-O-alpha-D-glucopyranoside, and EGCG 7-O-alpha-D-maltoside. One of these glucosides, EGCG 5-O-alpha-D-glucopyranoside, showed higher heat stability and solubility and lower astringency and astringent stimulation than its aglycon, suggesting that EGCG glucosides are functionally superior to EGCG as food additives.

The liverwort Marchantia polymorpha L. synthesizes arachidonic (ARA) and eicosapentaenoic acids (EPA) from linoleic and alpha-linolenic acids respectively by a series of reactions catalyzed by Delta6-desaturase, Delta6-elongase, and Delta5-desaturase. Overexpression of the M. polymorpha genes encoding these enzymes in transgenic M. polymorpha plants resulted in 3- and 2-fold accumulation of ARA and EPA respectively, as compared to those in the wild type. When these three genes were introduced and co-expressed in tobacco plants, in which long-chain polyunsaturated fatty acids (LCPUFAs) are not native cellular components, ARA and EPA represented up to 15.5% and 4.9% respectively of the total fatty acid in the leaves. Similarly in soybean, C20-LCPUFAs represented up to 19.5% of the total fatty acids in the seeds. These results suggest that M. polymorpha can provide genes crucial to the production of C20-LCPUFAs in transgenic plants.

The alpha-glucosidase of Bacillus sp. strain SAM1606 is a member of glycosyl hydrolase family 13, and shows an extraordinarily broad substrate specificity and is one of very few alpha-glucosidases that can efficiently hydrolyze the alpha-1,1-glucosidic linkage of alpha,alpha'-trehalose (trehalose). Phylogenetic analysis of family-13 enzymes suggests that SAM1606 alpha-glucosidase may be evolutionally derived from an alpha-1,6-specific ancestor, oligo-1,6-glucosidase (O16G). Indeed, replacement of Pro(273*) and Thr(342*) of B. cereus O16G by glycine and asparagine (the corresponding residues in the SAM1606 enzyme), respectively, was found to cause 192-fold enhancement of the relative catalytic efficiency for trehalose, suggesting that O16G may easily "evolved" into an enzyme with an extended substrate specificity by substitution of a limited number of amino acids, including that at position 273* (an asterisk indicates the amino-acid numbering of the SAM1606 sequence). To probe the role of the amino acid at position 273* of alpha-glucosidase in determination of the substrate specificity, the amino acid at position 273 of SAM1606 alpha-glucosidase was replaced by all other naturally occurring amino acids, and the resultant mutants were kinetically characterized. The results showed that substitution of bulky residues (e.g., isoleucine and methionine) for glycine at this position resulted in large increases in the K(m) values for trehalose and maltose, whereas the affinity to isomaltose was only minimally affected by such an amino-acid substitution at this position. Three-dimensional structural models of the enzyme-substrate complexes of the wild-type and mutant SAM1606 alpha-glucosidases were built to explore the mechanism responsible for these observations. It is proposed that substitution by glycine at position 273* could eliminate steric hindrance around subsite +1 that originally occurred in parental O16G and is, at least in part, responsible for the acquired broad substrate specificity of SAM1606 alpha-glucosidase.