Amylolytic Yeast Strain Research Articles

Application of industrial amylolytic yeast strains for the production of bioethanol from broken rice

Amylolytic Saccharomyces cerevisiae derivatives of Ethanol Red™ Version 1 (ER T12) and M2n (M2n T1) were assessed through enzyme assays, hydrolysis trials, electron microscopy and fermentation studies using broken rice. The heterologous enzymes hydrolysed broken rice at a similar rate compared to commercial granular starch-hydrolysing enzyme cocktail. During the fermentation of 20% dw/v broken rice, the amylolytic strains converted rice starch to ethanol in a single step and yielded high ethanol titers. The best-performing strain (ER T12) produced 93% of the theoretical ethanol yield after 96 h of consolidated bioprocessing (CBP) fermentation at 32 °C. Furthermore, the addition of commercial enzyme cocktail (10% of the recommended dosage) in combination with ER T12 did not significantly improve the maximum ethanol concentration, confirming the superior ability of ER T12 to hydrolyse raw starch. The ER T12 strain was therefore identified as an ideal candidate for the CBP of starch-rich waste streams.

Ethanol production from starch by yeasts isolated from crops and dairy products

The aim of this work was to study the ability ofyeasts isolated from crops and dairy products to convert starch to ethanol. The isolated yeasts were screened for their ability to hydrolyze starch. Six most active strains were identified as Lipomyces mesembrius spp. 5.4, 5.5 and 6.4, Shwanniomyces vanrijiae var yarowii F33, Torulaspora sp. F7 and Candida sp. S26. The selected yeasts produced low levels of ethanol from starch under aerobic conditions - 0.006-0.129 g/l (0.3-0.87 % of theoretical yield) and microaerobic conditions - 0. 089-0.35 g/l (1.61-6.07 % of theoretical yield). These amylolytic yeast strains will be studied as the potential candidates for the cocultivation with efficient ethanol producers which do not possess the ability to directly hydrolyze starch.

Stable expression of barley α-amylase in S. cerevisiae for conversion of starch into bioethanol

An industrial strain of Saccharomyces cerevisiae, NRRL Y-132, was genetically engineered to stably secrete barley α-amylase by introducing an expression cassette containing the α-amylase cDNA and a dominant selectable marker into the ribosomal DNA loci of the yeast chromosome. Batch fermentation studies with this strain showed that the integrated expression cassette was mitotically stable for over 100 generations of continuous culture. In addition, mutation of cysteine 95 to alanine in barley α-amylase was found to increase the recombinant strain's starch hydrolyzing ability. The integrated strain showed higher starch hydrolyzing ability and ethanol production on both soluble and raw starch than the strain transformed with an episomal-based yeast expression plasmid. The results indicate that integration of the gene cassette into multiple copy loci should be given consideration when designing amylolytic yeast strains.

Production and partial characterization of a thermostable amylase from ascomycetes yeast strain isolated from starchy soils

An amylolytic yeast strain was isolated from starchy soils (flour mills environment, flour market, cassava farms after harvesting and transformation of tubers) and its enzyme productivity and activity evaluated. The enzyme synthesis was optimum at 30°C when initial pH of fermentation medium was 4.5. After extraction and partial purification, the enzyme remained stable in a range of temperature and pH between 20°C-60°C and 2-8 pH respectively. The optimum enzyme activity was displayed at 70°C and pH 5.5 and 6.5. The thermostability of the enzyme was comparable to that of amylases from bacteria. Key Words: Amylolytic yeast, amylase activity, thermostable amylase. African Journal of Biotechnology Vol.4(1) 2005: 14-18

Medium optimization for glucoamylase production by a yeast, Pichia subpelliculosa ABWF-64, in submerged cultivation

An amylolytic yeast strain Pichia subpelliculosawas shown to produce glucoamylase in submerged cultivation. The yeast strain produced the enzyme optimally at 30 °C and pH 5.6 in shake flasks agitated at 200 rev min−1 in the optimized glucoamylase production medium containing 1% starch, 0.2% yeast extract, 0.4% K2HPO4, 0.035% NaCl and 0.1% MgCl2. Maximum enzyme production was attained during early growth of 11 h in shake flasks, and 6 h in a laboratory fermenter. By optimizing media components and cultivation parameters, a 15-fold increase in glucoamylase secretion was achieved.

Production of ethanol by raw starch hydrolysis and fermentation of damaged grains of wheat and sorghum

The simultaneous saccharification and fermentation was used to produce ethanol from raw starch of damaged quality wheat and sorghum grains by utilising crude amylase preparation from B. subtilis VB2 and an amylolytic yeast strain S. cerevisiae VSJ4. Various concentrations of damaged wheat and sorghum starch from 10% to 30%W/V were used and 25% was found to be optimum for damaged wheat and sorghum starch yielding 4.40%V/V and 3.50%V/V ethanol respectively. Whereas 25% raw starch of fine quality wheat and sorghum grains gave an yield of 5.60%V/V and 5.00%V/V respectively. The process was carried out at 35 °C, 5.8 pH and 200 rpm for 4 days.

Electrophoretic karyotype of the amylolytic yeast Lipomyces starkeyi and cloning, sequencing and chromosomal localization of its TRP1 gene.

The genome of the amylolytic yeast strain Lipomyces starkeyi NCYC 1436 was analysed using contour-clamped homogeneous electric field gel electrophoresis (CHEF). The banding pattern under a variety of running conditions indicating the presence of 11 different chromosome-sized DNA molecules. The sizes of these chromosome bands were determined by comparison with chromosomes from standard strains of Schizosaccharomyces pombe and Saccharomyces cerevisiae. The chromosomal bands were estimated to be within the range 0.7-2.8 Mb, with the genome (excluding mitochondrial DNA) estimated at 15 Mb. The molecular cloning of the TRP1 gene, isolated from a genomic library of this strain, is also reported: the gene was present on a 6.5-kb Sau3A DNA fragment, and complemented the trpC gene of E. coli. The DNA sequence was determined (EMBL accession No. Z68292) and compared to other tryptophan biosynthetic genes encoding N-(5'-phosphoribosyl) anthranilate isomerase (PRAI) activity. The gene was also used as a probe in hybridization studies, and by this means, its chromosomal location was identified.

Studies on an amylolytic strain of Saccharomyces cerevisiae isolated from yam tuber.

An amylolytic yeast strain identified as Saccharomyces cerevisiae was isolated from yam tuber. Studies on the effect of physical agents such as pH and temperature on the activity of the amylase showed that the optimum pH and temperature for the amylase produced by the S. cerevisiae were 5.0 and 60 degrees C, respectively. Heavy metal resistance study on the amylolytic yeast strain indicated different levels of resistance to copper (6.0 mM), zinc (3.0 mM) and manganese (15.0 mM) ions. The results are discussed in relation to the potential use of an amylolytic yeast in the brewing industry in Nigeria.

A novel raw-starch-digesting yeast α-amylase from Lipomyces starkeyi HN-606

An amylolytic yeast strain, isolated from Thai Loogpang Lauw and identified as Lipomyces starkeyi HN-606, was found to produce a novel yeast α -amylase characteristically showing raw-starch digestibility almost to the same extent as the commercial amylolytic Aspergillus , but with a lower culture temperature of 15°C rather than 25°C as optimal for growth. The yeast α -amylase (MW 56,000) was adsorbed onto raw corn-starch and could digest it to form glucose, maltose and maltotriose. α -Cyclodextrin at less than 10 mM completely inhibited the raw-starch adsorption and digestion with a K l value of 0.38 mM, but could hardly inhibit gelatinized-starch hydrolysis.

New Amylolytic Yeast Strains for Starch and Dextrin Fermentation

Yeast strains capable of fermenting starch and dextrin to ethanol were isolated from samples collected from Brazilian factories in which cassava flour is produced. Considerable alcohol production was observed for all the strains selected. One strain (DI-10) fermented starch rapidly and secreted 5 times as much amylolytic enzyme than that observed for Schwanniomyces alluvius UCD 54-83. This strain and three other similar isolates were classified as Saccharomyces cerevisiae var. diastaticus by morphological and physiological characteristics and molecular taxonomy.

Alcoholic fermentation of starch containing media using yeast protoplast fusion products

Fermentation of starch based industrial media was tested with yeast fusion products previously described, from a Baker's yeastSaccharomyces cerevisiae and Saccharomyces diastaticus and from a highly flocculentSaccharomyces cerevisiae andSaccharomyces diastaticus. The (somatic) fusion products were capable to produce more ethanol than parental strains after 96 h of batch fermentation. The aim of this work was to reduce the amount of enzyme used in saccharification by using good fermenting amylolytic yeast strains.

Direct alcoholic fermentation of starchy biomass using amylolytic yeast strains in batch and immobilized cell systems

Direct alcoholic fermentation of dextrin or soluble starch with selected amylolytic yeasts was studied in both batch and immobilized cell systems. In batch fermentations, Saccharomyces diastaticus was capable of fermenting high dextrin concentrations much more efficiently than Schwanniomyces castellii. From 200 g·l−1 of dextrin S. diastaticus produced 77 g·l−1 of ethanol (75% conversion efficiency). The conversion efficiency decreased to 59% but a higher final ethanol concentration of 120 g·l−1 was obtained with a medium containing 400 g·l−1 of dextrin. With a mixed culture of S. diastaticus and Schw. castellii 136 g·l−1 of ethanol was produced from 400 g·l−1 of dextrin (67% conversion efficiency). S. diastaticus cells attached well to polyurethane foam cubes and a S. diastaticus immobilized cell reactor produced 69 g·l−1 of ethanol from 200 g·l−1 of dextrin, corresponding to an ethanol productivity of 7.6g·l−1·h−1. The effluent from a two-stage immobilized cell reactor with S. diastaticus and Endomycopsis fibuligera contained 70 g·l−1 and 80 g·l−1 of ethanol using initial dextrin concentrations of 200 and 250 g·l−1 respectively. The corresponding values for ethanol productivity were 12.7 and 9.6 g·l−1·h−1. The productivity of the immobilized cell systems was higher than for the batch systems, but much lower than for glucose fermentation.

Production of extracellular debranching activity by amylolytic yeasts

The production of extracellular pullulan-degrading enzymes by several amylolytic yeast strains was studied. The highest activity was obtained with species of Endomycopsis, Lipomyces, Filobasidium, Leucosporidium, and Trichosporon, and also with some amylase-hyperproducing mutants. The most active strains are potentially valuable partners for intergeneric protoplast fusion.