68 research outputs found
Targeted discovery and functional characterisation of complex-xylan degrading enzymes
No full textThis thesis describes the development of a screening method to discover efficient hemicellulase producers in a wide range of fungi. The method is based on the potential of soil fungi to degrade soluble and insoluble xylan-rich substrates, by assigning various individual enzyme activities. Released mono- and oligosaccharides were monitored by high performance anion exchange chromatography and matrix assisted laser desorption/ionisation time-of-flight mass spectrometry. In addition, the released amounts of acetic acid were measured. Fungal strains, grown on wheat straw, with an efficient production of hemicellulolytic enzymes were Aspergillus lentulus, Penicllium pinophilum, and Trichoderma harzianum. Next, two glycoside hydrolase (GH) family 10 endo-xylanases and two GH11 endo-xylanases of Myceliophthora thermophila C1 (C1) were subjected to a detailed characterisation. The degradation products from xylan-rich substrates, varying in type and degree of substituents, displayed that both intra- and interfamily differences occurred for these endo-xylanases. The different degradation profiles were correlated with a difference in the predicted secondary protein structure of the GH10 xylanases and with a minor difference in the primary protein structure of the GH11 xylanases. An additional cellulose binding domain attached to the endo-xylanases did not enhance the degradation of insoluble substrates. In addition, synergy studies were performed on acetyl (xylan) esterases with glucuronidases. A concerted action of acetyl (xylan) esterases from different carbohydrate esterase families as well as synergy with glucuronidases of different GH families was observed
Targeted discovery and functional characterisation of complex-xylan degrading enzymes
No full text This thesis describes the development of a screening method to discover efficient hemicellulase producers in a wide range of fungi. The method is based on the potential of soil fungi to degrade soluble and insoluble xylan-rich substrates, by assigning various individual enzyme activities. Released mono- and oligosaccharides were monitored by high performance anion exchange chromatography and matrix assisted laser desorption/ionisation time-of-flight mass spectrometry. In addition, the released amounts of acetic acid were measured. Fungal strains, grown on wheat straw, with an efficient production of hemicellulolytic enzymes were Aspergillus lentulus, Penicllium pinophilum, and Trichoderma harzianum. Next, two glycoside hydrolase (GH) family 10 endo-xylanases and two GH11 endo-xylanases of Myceliophthora thermophila C1 (C1) were subjected to a detailed characterisation. The degradation products from xylan-rich substrates, varying in type and degree of substituents, displayed that both intra- and interfamily differences occurred for these endo-xylanases. The different degradation profiles were correlated with a difference in the predicted secondary protein structure of the GH10 xylanases and with a minor difference in the primary protein structure of the GH11 xylanases. An additional cellulose binding domain attached to the endo-xylanases did not enhance the degradation of insoluble substrates. In addition, synergy studies were performed on acetyl (xylan) esterases with glucuronidases. A concerted action of acetyl (xylan) esterases from different carbohydrate esterase families as well as synergy with glucuronidases of different GH families was observed.</p
Diversity in Production of Xylan-Degrading Enzymes Among Species Belonging to the Trichoderma Section Longibrachiatum
No full textXylan is an important part of plant biomass and represents a renewable raw material for biorefineries. Contrary to cellulose, the structure of hemicellulose is quite complex. Therefore, the biodegradation of xylan needs the cooperation of many enzymes. For industrial production of xylanase multienzyme complexes (cocktails) and selected monocomponent xylanases, different Trichoderma reesei mutants and recombinants are used. T. reesei QM 6a (wild-type parent of best existing mutants) was selected as a starting material in the 1960s when the modern in-depth analytical methods were not yet in use. Therefore, screening of fungi genetically close to T. reesei in biodegradation of xylan may have a scientific value. Fifteen different strains from Trichoderma section Longibrachiatum have been tested for extracellular xylan-degrading enzyme production on three carbon sources (wheat straw, corn fiber, and eucalyptus wood) in shake flask cultivation. The enzyme activities were evaluated by traditional colorimetric enzyme assays and by HPLC and matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Degradation of xylan was studied on four different xylan-rich model substrates. T. reesei CPK 155, Trichoderma parareesei TUB F-2535, and Trichoderma gracile TUB F-2543 isolates were equally good or better in degradation of the wheat arabinoxylan (WAX) and corn fiber alcohol insoluble solids as hydolysis substrates than the well-known T. reesei QM 6a and RUT C30 strains. Though Trichoderma saturnisporum ATCC 18903 gave relatively low volumetric enzyme activities by traditional colorimetric assays, it could release quite large amount of hydrolysis products (mono- and oligosaccharides) from WAX. Therefore, these fungi may be potential candidates for further experiments. Enzyme production on wheat straw and corn fiber carbon sources was more effective than on eucalyptus woo
Performance of hemicellulolytic enzymes in culture supernatants from a wide range of fungi on insoluble wheat straw and corn fiber fractions
No full textFilamentous fungi are a good source of hemicellulolytic enzymes for biomass degradation. Enzyme preparations were obtained as culture supernatants from 78 fungal isolates grown on wheat straw as carbon source. These enzyme preparations were utilized in the hydrolysis of insoluble wheat straw and corn fiber xylan rich fractions. Up to 14% of the carbohydrates in wheat straw and 34% of those in corn fiber were hydrolyzed. The degree of hydrolysis by the enzymes depended on the origin of the fungal isolate and on the complexity of the substrate to be degraded. Penicillium, Trichoderma or Aspergillus species, and some non-identified fungi proved to be the best producers of hemicellulolytic enzymes for degradation of xylan rich materials. This study proves that the choice for an enzyme preparation to efficiently degrade a natural xylan rich substrate, is dependent on the xylan characteristics and could not be estimated by using model substrates
Production of oligosaccharides from extruded wheat and rye biomass using enzymatic treatment
No full textResearch on prebiotics and other novel healthpromoting food components has been active for over a decade. Arabinoxylan (AX) derived arabinoxylooligosaccharides (AXOS), which may have various chemical structures, depending on the xylan source and the degradation method used, stand increasingly in the spotlight as potential prebiotics. During the past decade, the studies of the possibilities to produce the AXOS by using biocatalytic conversion have received more attention. In addition, there is an interest in the use of novel cereal biomass for the production of AXOS. The aim of this study was to investigate the influence of various commercial enzyme preparations on the degradability of insoluble arabinoxylans in wheat and rye wholemeal treated by extrusion, identify and quantify xylooligosaccharides (XOS) and arabinoxylooligosaccharides (AXOS) in treated media. The enzymatic degradation of rye and wheat cell wall materials was monitored by HPSEC, HPAEC and MALDITOFMS techniques. It was noticed that there is no significant difference between extruded and natural cereals, and type of cereals had not significant influence on XOS and AXOS production. The most effective biocatalysts were hemicellulases expressed in the enzyme preparations from Trichoderma and Aspergillus spp. (Depol 692), Humicola and Bacillus spp. (Ceremix Plus). Degradability of rye and wheat cell wall materials by these enzyme preparations obtained break down percentages of 70–87% and 67–77%, respectively. After enzymatic treatment, only small amounts of xylose, xylobiose, and xylotriose was eluted compare to the amount of more complex oligosaccharides with higher degree of polymerization (DP). The mass spectra of oligosaccharides indicated the presence of a homologous series of pentoses ranging from DP 4 to 15. This indicates that chosen enzyme preparations acted well on wheat and rye biomass, and released quite high amounts of XOS and AXOS
ClassCut for Unsupervised Class Segmentation
No full textWe propose a novel method for unsupervised class segmentation on a set of images. It alternates between segmenting object instances and learning a class model. The method is based on a segmentation energy defined over all images at the same time, which can be optimized efficiently by techniques used before in interactive segmentation. Over iterations, our method progressively learns a class model by integrating observations over all images. In addition to appearance, this model captures the location and shape of the class with respect to an automatically determined coordinate frame common across images. This frame allows us to build stronger shape and location models, similar to those used in object class detection. Our method is inspired by interactive segmentation methods [1], but it is fully automatic and learns models characteristic for the object class rather than specific to one particular object/image. We experimentally demonstrate on the Caltech4, Caltech101, and Weizmann horses datasets that our method (a) transfers class knowledge across images and this improves results compared to segmenting every image independently; (b) outperforms Grabcut [1] for the task of unsupervised segmentation; (c) offers competitive performance compared to the state-of-the-art in unsupervised segmentation and in particular it outperforms the topic model [2]
Structural features and properties of soluble products derived from Eucalyptus globulus hemicelluloses
No full textEucalyptus globulus wood samples were subjected to double hydrothermal processing to remove extractives in the first stage, and to cause the selective solubilisation of 4-O-methylglucuronoxylan in the second stage. The hemicellulose-derived products present in the liquors from the second hydrothermal stage (substituted xylooligosaccharides, denoted XOS) were refined by treatments with membranes and ion exchange. The purified XOS product was assayed for composition and characterised by HPLC-RI, HPAEC-PAD, HPSEC, MALDI-TOF-MS and NMR techniques. The results suggested the presence of neutral and acidic XOS with a degree of acetylation of about 0.6. The fermentability of the refined XOS product by faecal inocula was assessed by measuring both substrate consumption and formation of short-chain fatty acids
Production, Refining, Structural Characterization and Fermentability of Rice Husk Xylooligosaccharides
No full textOligosaccharides produced by hydrothermal processing of rice husks (xylooligosaccharides and glucooligosaccharides) were refined by membrane processing (operating in diafiltration and concentration modes), subjected to xylanase treatment to reduce the average molar mass, and subjected to further purification by ultrafiltration (operating in concentration mode) and ion exchange. The purified products were assayed for composition, molar mass distribution and structural characterization by HPLC, HPAEC-PAD, HPSEC, MALDI-TOF-MS and NMR (1H and 13C). The fermentability of the purified product by fecal inocula was assessed on the basis of the time courses of pH and oligosaccharide concentrations. Succinate, lactate, formiate, acetate, propionate and butyrate were the major products resulting from fermentation experiments
Screening for distinct xylan degrading enzymes in complex shake flask fermentation supernatants
No full textThe efficient degradation of complex xylans needs collaboration of many xylan degrading enzymes. Assays for xylan degrading activities based on reducing sugars or PNP substrates are not indicative for the presence of enzymes able to degrade complex xylans: They do not provide insight into the possible presence of xylanase-accessory enzymes within enzyme mixtures. A new screening method is described, by which specific xylan modifying enzymes can be detected. Fermentation supernatants of 78 different fungal soil isolates grown on wheat straw were analyzed by HPLC and MS. This strategy is powerful in recognizing xylanases, arabinoxylan hydrolases, acetyl xylan esterases and glucuronidases. No fungus produced all enzymes necessary to totally degrade the substrates tested. Some fungi produce high levels of xylanase active against linear xylan, but are unable to degrade complex xylans. Other fungi producing relative low levels of xylanase secrete many useful accessory enzyme component(s)
The Association of Apathy With Incident Dementia: A Multiple Mediation Analysis of Cardiovascular Risk Factors.
No full textContains fulltext :
319213.pdf (Publisher’s version ) (Open Access)OBJECTIVES: Despite established links between apathy, cardiovascular disease, and dementia, it remains unclear if cardiovascular risk factors (CVRF) play a mediating role in the association between apathy and dementia. If apathy increases dementia risk via lifestyle-related dementia risk factors, targeted lifestyle interventions could help high-risk individuals. METHODS: We used data from the preDIVA study including 3303 individuals aged 70-78 years. Apathy was assessed using the geriatric depression scale, and CVRF (cardiovascular risk factors) (systolic blood pressure, cholesterol, diabetes, body mass index (BMI), smoking, and physical activity) were considered as potential mediators. Outcome was incident dementia during 12 years of follow-up. We assessed mediation using Multiple Mediation Analysis (MMA). RESULTS: Of the association between apathy and dementia (HR 1.49 [95% CI 0.99-2.41]), 27% was mediated by physical inactivity, BMI and diabetes combined. Of this total, physical inactivity mediated 28% of the effect (HR 1.12, 95% CI 1.03-1.29), diabetes 9% of the effect (HR 1.04, 95% CI 1.02-1.10), and BMI counteracted these effects by -12% (HR 0.95, 95% CI 0.88-0.98). CONCLUSION: The relationship between apathy and dementia is partly mediated by physical inactivity, BMI and diabetes. Apathy is an important clinical marker that signals the existence of potentially modifiable pathways, providing an opportunity for lifestyle interventions. To potentially reduce dementia risk via lifestyle modification in patients with apathy, a tailored approach should be taken to overcome the characterizing symptom of diminished motivation
- …
