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Effects of alkaline or liquid-ammonia treatment on crystalline cellulose: Changes in crystalline structure and effects on enzymatic digestibility

Posted: October 23, 2011 at 3:53 pm

Background:
In converting biomass to bioethanol, pretreatment is a key step intended to render cellulose more amenable and accessible to cellulase enzymes and thus, increase glucose yields. In this study, four cellulose samples with different degrees of polymerization and crystallinity indexes were subjected to aqueous NaOH and anhydrous liquid ammonia treatments. The effects of the treatments on cellulose crystalline structure were studied, in addition to the effects on the digestibility of the celluloses by a cellulase complex.
Results:
From X-ray diffractograms and NMR spectra, it was revealed that treatment with liquid-ammonia produced the cellulose III allomorph; however, crystallinity depended on treatment conditions. Treatment at low temperature (25degreesC) resulted in a less crystalline product, whereas treatment at elevated temperatures (130degreesC or 140degreesC) gave a more crystalline product. Treatment of cellulose I with aqueous NaOH (16.5 wt%) resulted in formation of cellulose II, but also produced a much less crystalline cellulose. The relative digestibilities of the different cellulose allomorphs were tested by exposing the treated and untreated cellulose samples to a commercial enzyme mixture (Genencor-Danisco; GC 220). The digestibility results showed that the starting cellulose I samples were the least digestible (except for corn stover cellulose, which had a high amorphous content). Treatment with NaOH produced the most digestible cellulose, followed by treatment with liquid-ammonia at low temperature. Factor analysis indicated that initial rates of digestion (up to 24 h) were most strongly correlated with amorphous content. Correlation of allomorph type with digestibility was weak, but was strongest with cellulose conversion at later times. The cellulose III samples produced at higher temperature had comparable crystallinities to the initial cellulose I samples, but achieved higher levels of cellulose conversion, at longer digestion times.
Conclusions:
Earlier studies have focused on determining which cellulose allomorph is the most digestible. In this study we have found that the chemical treatments to produce different allomorphs also changed the crystallinity of the cellulose, and this had a significant effect on the digestibility of the substrate. When determining the relative digestibilities of different cellulose allomorphs it is essential to also consider the relative crystallinities of the celluloses being tested.Source:
http://www.biotechnologyforbiofuels.com/rss/

Recommendation and review posted by G. Smith

Transcriptome analysis of Aspergillus niger grown on sugarcane bagasse

Posted: October 23, 2011 at 3:53 pm

Background:
Considering that the costs of cellulases and hemicellulases contribute substantially to the price of bioethanol, new studies to understand and improve cellulase efficiency and productivity are of paramount importance. Aspergillus niger has been shown to produce a wide spectrum of polysaccharide-hydrolytic enzymes. In order to understand how to improve enzymatic cocktails that can hydrolyze pre-treated sugarcane bagasse, we used a genomics approach to investigate which genes and pathways are transcriptionally modulated during growth of A. niger on steam-exploded sugarcane bagasse (SEB).
Results:
Here, we report the main cellulase- end hemicellulase-encoding genes with increased expression during growth on SEB. We also examined if the mRNA accumulation of several SEB-induced genes encoding putative transporters was induced by xylose and dependent on glucose. We identified 18 (58 % of A. niger predicted cellulases) and 21 (58 % of A. niger predicted hemicellulases) cellulases- and hemicellulases-encoding genes, respectively, that were highly expressed during growth on SEB.
Conclusions:
Degradation of sugarcane bagasse requires production of many different enzymes, which are regulated by the type and complexity of the available substrate. Our work opens new possibilities for understanding sugarcane biomass saccharification by A. niger hydrolases and for the construction of more efficient enzymatic cocktails for second generation bioethanol.Source:
http://www.biotechnologyforbiofuels.com/rss/

Recommendation and review posted by G. Smith

A cellular automaton model of crystalline cellulose hydrolysis by cellulases

Posted: October 23, 2011 at 3:53 pm

Background:
Cellulose from plant biomass is an abundant, renewable material which could be a major feedstock for low emissions transport fuels such as cellulosic ethanol. Cellulase enzymes that break down cellulose into fermentable sugars are composed of different types - cellobiohydrolases I and II (CBHI and CBHII), endoglucanase (EG) and beta-glucosidase (BG) - with separate functions. They form a complex interacting network between themselves, soluble hydrolysis product molecules, solution and solid phase substrates and inhibitors. There have been many models proposed for enzymatic saccharification, however, none have yet employed a cellular automaton approach which allows important phenomena such as enzyme crowding on surface of solid substrates, denaturation and substrate inhibition to be considered in the model.
Results:
The Cellulase 4D model was developed de novo taking into account the size and composition of the substrate and surface-acting enzymes were ascribed behaviors based on their movements, catalytic activities and rates, affinity for, and potential for crowding of, the cellulose surface, substrates and inhibitors, and denaturation rates. A basic case modeled on literature-derived parameters obtained from Trichoderma reesei cellulases resulted in cellulose hydrolysis curves that closely matched curves obtained from published experimental data. Scenarios were tested in the model which included variation of enzyme loadings, adsorption strengths of surface acting enzymes and reaction periods, and the effect on saccharide production over time was assessed. The model simulations indicated an optimal enzyme loading of between 0.5 and 2 of the base case concentrations where a balance was obtained between enzyme crowding on the cellulose crystal, and that the affinities of enzymes for the cellulose surface had a large effect on cellulose hydrolysis. In addition, improvements to the CBHI activity period substantially improved overall glucose production.
Conclusions:
Cellulase 4D simulates the enzymatic hydrolysis of cellulose to glucose by surface and solution phase-acting enzymes and accounts for complex phenomena that have previously not been included in cellulose hydrolysis models. The model is intended as a tool for industry, researchers and educators alike to explore options for enzyme engineering and process development and to test hypotheses regarding cellulase mechanisms.Source:
http://www.biotechnologyforbiofuels.com/rss/

Recommendation and review posted by G. Smith

Exposing the fraud and mythology of conventional cancer treatments

Posted: October 23, 2011 at 3:53 pm

Treating cancer is BIG business in America -- in fact, it's a $200 billion a year business. Yet 98 percent of conventional cancer treatments not only FAIL miserably, but are also almost guaranteed to make cancer patients sicker.

What's worse: The powers are suppressing natural cancer cures that could help tens of thousands of people get well and live cancer free with little or no dependence on drugs, surgery and chemotherapy.

The treatment of cancer in the U.S. is one of the most bald-faced cover-ups in medical history. Enough is enough! You deserve to know the truth about the criminality of oncologists and about the dangers of chemotherapy, conventional cancer treatments and the cancer "business."

Chemotherapy kills more than cancer
Want proof? Did you know that 9 out of 10 oncologists would refuse chemotherapy if they had cancer? That's up to 91% -- a huge percentage that clearly shines a light on the truth: chemotherapy kills. Conventional oncologists are not only allowing this to happen, but they're also bullying many patients into chemotherapy and surgery right after their diagnoses. Read more...

Ayurtox for Body Detoxification

Source:
http://feeds.feedburner.com/integratedmedicine

Recommendation and review posted by G. Smith

The post-reproductive Fallopian tube: better removed?

Posted: October 23, 2011 at 3:53 pm

Recently, the distal Fallopian tube has attracted considerable attention not only as site of origin for serous cancer in women with BRCA mutations, but also as the anatomical location where the majority of serous ovarian cancers apparently develop. Consequently, the Fallopian tube may be the unique location where early ‘ovarian’ cancers can be found—which would contradict the long-standing impression that the ovaries and the Fallopian tubes are always simultaneously involved. Based on the dismal prognosis associated with ovarian cancer and our inability to screen for early-stage disease, we discuss the rationale for introducing salpinges-hysterectomy as new clinical standard for women in need of hysterectomy and further weigh the arguments for and against bilateral salpingectomy as a sterilization method. There is no known physiological benefit of retaining the post-reproductive Fallopian tube during hysterectomy or sterilization, especially as this does not affect ovarian hormone production. On the other hand, the consequences associated with a surgical menopause provide a rationale for preserving the ovaries in premenopausal women. Prophylactic removal of the Fallopian tubes during hysterectomy or sterilization would rule out any subsequent tubal pathology, such as hydrosalpinx, which is observed in up to 30% of women after hysterectomy. Moreover, this intervention is likely to offer considerable protection against later tumour development, even if the ovaries are retained. Thus, we recommend that any hysterectomy should be combined with salpingectomy. In addition, women over 35 years of age could also be offered bilateral salpingectomy as means of sterilization.

Source:
http://humrep.oxfordjournals.org/rss/current.xml

Recommendation and review posted by G. Smith

Anti-Mullerian hormone–is it a crystal ball for predicting ovarian ageing?

Posted: October 23, 2011 at 3:53 pm

Several studies have demonstrated that anti-Müllerian hormone (AMH) is a better marker of ovarian reserve than age, basal FSH, estradiol and inhibin. AMH is very good in (i) predicting both over- and poor-response in the controlled ovarian stimulation environment, (ii) determining the most appropriate stimulation regimen and (iii) pre-treatment counselling for couples to make an appropriate and informed choice. Recent reports are exploring the use of AMH in various other indications, including (i) predicting long-term fertility and guiding how long a woman can delay childbearing without facing the risk of reduced ovarian reserve, (ii) predicting the age of menopause, (iii) prediction of ovarian ageing in women prior to or following chemotherapy, (iv) prediction of long-term fertility following ovarian surgery and (v) screening for polycystic ovaries. However, widespread use of AMH for indications not proved by evidence-based medicine can lead to either false reassurance or distress, leading to unnecessary medical interventions . It also has huge implications for costs. We evaluated the evidence basis for using AMH for various indications to decide how justified it is to promote AMH as a crystal ball, until more evidence is available.

Source:
http://humrep.oxfordjournals.org/rss/current.xml

Recommendation and review posted by G. Smith


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