Ethanol-Herstellung mit Bakterien

Ethanol production with bacteria . Strains of Saccharomyces cerevisiae have mostly been used for the production of ethanol from sugar by yeasts. Recently it was shown that the bacterium Zymomonas mobilis has some advantages compared to yeast for the production of industrial alcohol. Compared to traditional yeast fermentation, ethanol yield is about 5% higher than with yeast, since less sugar is incorporated into cell material by this bacterium. Like yeast, Zymomonas mobilis has remarkably high ethanol tolerance which enables the bacterium to produce ethanol concentrations of more than 13 vol.-% from sugar solutions of appropriate concentration. Investigations of the spectrum of lipids present have shown that this bacterium contains large quantities of hopanoids which are presumably of significance for the stabilization of cell membranes in the presence of ethanol. Since the cost of the sugar greatly influences the profitability fraction formed in the production of glucose syrup from wheat flour was investigated. It was shown that after enzymatic saccharification of this waste starch the glucose was efficiently fermented to ethanol by Zymomonas mobilis. It is planned to broaden the substrate spectrum of Zymomonas mobilis by gene cloning techniques so that in future pentoses, e. g. xylose or arabinose, can also be fermented to ethanol by this organism.     

Induction of xylose reductase and xylitol dehydrogenase activities on mixed sugars in Candida guilliermondii

The ability of various sugars to induce xylose reductase (aldose reductase, EC 1.1.1.21) and xylitol dehydrogenase (D -xylulose reductase, EC 1.1.1.9) activities in Candida guilliermondii was studied. D -Xylose was found to be the best inducer of activities of both enzymes, followed closely by L -arabinose. Very low xylose reductase activity was induced by cellobiose, D -mannose, D -glucose, D -galactose, D -fructose or glycerol. With xylitol dehydrogenase, cellobiose and D -fructose caused partial induction of enzyme activity, while negligible activity was induced by D -mannose, D -glucose, D -galactose or glycerol. Several sugars were tested for the ability to repress the induction by D -xylose of xylose reductase and xylitol dehydrogenase activities in C. guilliermondii. Enzyme activities induced on D -xylose served as controls. L -Arabinose, cellobiose and D -galactose did not repress enzyme induction by D -xylose, while D -mannose, D -glucose and D -fructose repressed enzyme induction to varying extents. Results from enzyme induction generally correlated with patterns of mixed sugar utilization, with some anomalies associated with the utilization of D -galactose and D -fructose in the presence of D -xylose. The results show that the utilization of D -xylose by C. guilliermondii is subject to regulation by induction and catabolite repression.     

Signal transduction and regulation in bacteria

To understand both the complex structure and behavior of signal transduction and regulation in bacterial cells requires an overall holistic approach. Due to the multitude of interacting components an understanding of these processes just by reflection is not possible. Here, the aid of mathematical modeling is absolutely essential to confirm the available biological knowledge by system theoretical analysis. Two examples of a global regulatory system, namely catabolite repression in Escherichia coli and redox control in Rodospirillum rubrum are discussed and compared. The regulation of stress sigma factor σ^S in E. coli is then dealt with as an example of regulated gene expression combined with proteolysis. Finally, phototaxis in Halobacterium salinarum is considered as a representative of a bacterial signal transduction system. Important questions are related to the modularity and the hierarchical structure of these systems. The goal is to decompose a signaling or regulatory system into components of elementary signal transfer and to discover common features of there systems.     

A comparison of oxygen mass transfer into sodium sulphite solution and a biological system

To explain previously reported discrepancies between oxygen uptake rates in biological systems and the sodium sulphite test system a comparison was made between oxygen mass transfer into a sodium sulphite solution catalysed by copper(II) ions, and into a biological system, the bacterium E. coli in a mineral medium. A stirred transfer cell, with a relatively low rate of physical mass transfer per unit area, and a bubble column, with a high physical mass transfer rate per unit area, were used to make this comparison; in both cases, the areas of gas/liquid contact could be determined. In the transfer cell the gas/liquid mass transfer coefficient for the biological system was only 10–25% of that for the sulphite oxidation system (for which the absorption rate was increased by chemical reaction). In the bubble column mass transfer into both systems was controlled by physical absorption and the mean mass transfer coefficients were similar for both systems. However, the mass transfer coefficient for the biological system increased with E. coli concentration, probably due to physical effects of the small particles.     

Efficient production of glutathione using hydrolyzate of banana peel as novel substrate

The hydrolyzate of banana peels containing abundant fermentable sugars as glucose, xylose, mannose, and arabinose was successfully used as a novel substrate for the efficient production of glutathione by Candida utilis SZU 07-01. Xylose was first selected as the sole carbon source for glutathione production, medium optimization for better cell growth and higher glutathione using response surface methodology consisting of PB design, the steepest ascent experiment and CCD was carried out, and the optimal combination of nutrients was obtained as follows: xylose 20 g/L, (NH₄)₂SO₄ 9.59 g/L, KH₂PO₄ 3 g/L, L-methionine 5.72 g/L and MgSO₄ 0.20 g/L. The maximum dry cell weight and glutathione achieved using the optimized medium were 7.36 g/L and 154.32 mg/L, respectively. Following with the content in this medium, other sugars like glucose, mannose and arabinose were chosen as the sole carbon source and all tested available for glutathione production. Based on these results, the hydrolyzate of banana peels was selected as a novel substrate, and a high DCW of 7.68 g/L and glutathione yield of 111.33 mg/L were obtained with the initial sugar concentration of 20 g/L in the hydrolyzate of banana peels.     

Low-Temperature Dilute Acid Hydrolysis of Oil Palm Frond

Oil palm frond (OPF) fiber, a lignocellulosic waste from the palm oil industry, contains high cellulose and hemicellulose content, thus it is a potential feedstock for simple sugars production. This paper describes the two-stage hydrolysis process focusing on the use of low-temperature dilute acid hydrolysis to convert the hemicellulose in OPF fiber to simple sugars (xylose, arabinose, and glucose). The objective of the present study was to evaluate the effect of operating conditions of dilute sulfuric acid hydrolysis undertaken in a 1 L self-built batch reactor on xylose production from OPF fiber. The reaction conditions were temperatures (100–140°C), acid concentrations (2–6%), and reaction times (30–240 min). The mass ratio of solid/liquid was kept at 1:30. Analysis of the three main sugars glucose, xylose, and arabinose were determined using high-pressure liquid chromatography. The optimum reaction temperature, reaction time, and acid concentration were found to be 120°C, 120 min, and 2% acid, respectively. Based on the potential amount of xylose (10.8 mg/mL), 94% conversion (10.15 mg/mL) was obtained under the optimum conditions with small amount of furfural (0.016 mg/mL). To enhance the effectiveness of dilute acid hydrolysis, the hydrolysis of OPF fiber was also performed using ultrasonic-pretreated OPF fiber. The effects of ultrasonic parameters power (40–80%) and ultrasonication times (20–60 min) were determined on sugar yields under optimum hydrolysis conditions (2% acid sulfuric, 120°C and 120 min). However, the use of ultrasonication was found to have detrimental effect on the yield of simple sugars due to the 10-fold increase in the formation of furfural.     

Kinetics of Bioethanol Production Employing Mono‐ and Co‐Cultures of Saccharomyces cerevisiae and Pichia stipitis

The kinetics of bioethanol production using mono‐ and co‐cultures of Saccharomyces cerevisiae and Pichia stipitis with glucose, xylose, and glucose‐xylose sugar mixtures were investigated. A MATLAB® program was formulated for simulation of experimental results in order to get predicted values of ethanol production and sugar consumption and for kinetic parameter estimation. Kinetic parameters implied less extent of substrate and/or product inhibition when the co‐culture scheme of immobilized S. cerevisiae and free P. stipitis was employed for fermentation of mixed sugars. In addition, a high ethanol yield was achieved by applying this co‐culture strategy to wheat straw hydrolysates.     

Comparison of alkali and steam (acid) pretreatments of lignocellulosic materials to increase enzymic susceptibility: Evaluation under optimised pretreatment conditions

The alkali pretreatment of sugar cane bagasse was optimised and compared with an optimised steam (acid) pretreatment. The optimised alkali pretreatment gave an overall sugar yield of 37.4 g sugars per 100 g bagasse accounting for 43.8% of the initial xylan and 64.5% of the glucan. Potential effluent problems were identified with the alkali treatment and several strategies were suggested to minimise them, with liquor recycling showing some promise. The optimised steam (acid) pretreatment gave an overall sugar yield of 55.7 g sugars per 100 g bagasse accounting for 76.5% of the xylan and 89.5% of the glucan. The superiority of the steam (acid) pretreatment over the alkali pretreatment depends on the ability to utilise the xylose produced.     

The hydrothermal degradation of cellulosic matter to sugars and their fermentative conversion to protein

For the hydrothermal degradation of cellulosic matter, an apparatus was developed in which water is used as extraction medium. Samples, 0.15 g each, of pure cellulose (filter paper), natural straw, and ¹⁴C-labeled straw were treated at temperatures of between 200° and 275°C. Of the inserted cellulose, 65.7% was recovered at the optimum temperature as sugars and hydroxymethylfurfural. It was possible to degrade the straw selectively: at lower temperatures, the hemicellulose part of the plant matter was converted to xylose and arabinose; and then at higher temperatures, the cellulose was converted to glucose and cellobiose. At the same time, a certain amount of the sugars was transformed to furfural compounds. The growth behavior of the yeast Candida utilis (strain Weissenbach) was analyzed, using cellobiose, xylose, and glucose (standard) as carbon sources. The growth curves applying cellobiose were nearly identical to those of glucose. Xylose showed lower productivity than the hexoses. The main products of the hydrothermal degradation can, therefore, be used favorably as nutritive substances for this proteinproducing yeast.     

微扰理论计算氨基酸和糖水溶液的密度

基于微扰理论并借助于统计缔合流体理论的基本思路,建立了氨基酸和糖水溶液密度的状态方程.计算了甘氨酸、丙氨酸、缬氨酸、氨基丁酸和丝氨酸水溶液体系在4个温度下的密度,以及葡萄糖、果糖、半乳糖、树胶醛糖和木糖水溶液体系在5个温度下的密度.此外采用所建立的方程,不引入任何可调参数,直接对氨基酸在尿素水溶液中的密度进行了预测.关联和预测的结果均令人满意.     

Investigating glucose and xylose metabolism in Saccharomyces cerevisiae and Scheffersomyces stipitis via 13C metabolic flux analysis

¹³C metabolic flux analysis (¹³C? MFA) has been extensively applied in studying the glucose metabolism of yeast strains such as Saccharomyces cerevisiae and Scheffersomyces stipitis. Here, we tried to augment the previous fluxomic studies by applying ¹³C? MFA to rigorously investigate the metabolic flux distributions in S. stipitis and the recombinant S. cerevisiae strains when xylose was utilized as the sole carbon substrate. It was found that less carbon fluxes were diverted into the TCA cycle in S. stipitis than the recombinant S. cerevisiae strains. Compared to single sugar utilization, the co‐utilization of glucose and xylose by S. stipitis led to increased metabolic fluxes into the futile pathway and the TCA cycle, but did not improve sugar‐based ethanol yield. In addition, heterologous expression of xylose pathway in engineered S. cerevisiae strains may affect the glucose utilization. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3195–3202, 2013     

虫草菌中多糖的气相色谱分析

采用气相色谱法研究自虫草菌中分离、纯化的多糖的单糖组成,结果表明其单糖的摩尔组成分别为阿拉伯糖：1,木糖：2,甘露糖：1,葡萄糖：3,半乳糖：3。     

Solvent extraction and purification of sugars from hemicellulose hydrolysates using boronic acid carriers

Research was performed to determine whether it was technically feasible to use boronic acid extractants to purify and concentrate the sugars present in hemicellulose hydrolysates. Initially, five types of boronic acids (phenylboronic acid, 3,5‐dimethylphenylboronic acid, 4‐tert‐butylphenylboronic acid, trans‐β‐styreneboronic acid or naphthalene‐2‐boronic acid) dissolved in an organic diluent (Shellsol^® 2046 or Exxal^® 10) containing the quaternary amine Aliquat^® 336 were tested for their ability to extract sugars (fructose, glucose, sucrose and xylose) from a buffered, immiscible aqueous solution. Naphthalene‐2‐boronic acid was found to give the greatest extraction of xylose regardless of which diluent was used. Trials were then conducted to extract xylose and glucose from solutions derived from the dilute acid hydrolysis of sugar cane bagasse and to then strip the loaded organic solutions using an aqueous solution containing hydrochloric acid. This produced a strip solution in which the xylose concentration had been increased over 7× that of the original hydrolysate while reducing the concentration of the undesirable acid‐soluble lignin by over 90%. Hence, this process can be exploited to produce high concentration xylose solutions suitable for direct fermentation. Copyright © 2004 Society of Chemical Industry     

Chemical characterization and liberation of pentose sugars from brewer's spent grain

The chemical composition of brewer's spent grain (BSG), generated from a process using 100% malted barley, was investigated. BSG is mainly composed of (g kg^?1) hemicellulose (284), lignin (278), cellulose (168) and protein (152.5), but it also contains extractives and ashes in smaller proportions. Minerals in BSG include calcium, sodium, potassium, magnesium, aluminum, iron, barium, strontium, manganese, copper, zinc, phosphorus, sulfur, chromium and silicon. In order to find alternative uses for BSG, this by‐product was subjected to acid hydrolysis process to recover the hemicellulosic sugars, which have a large number of industrial applications. The process was carried out under different conditions of liquid‐to‐solid ratio and acid concentration to evaluate the influence of these two variables on BSG hemicellulose hydrolysis. Under all the hydrolysis conditions evaluated, arabinose was recovered with higher efficiency than xylose. Under the best evaluated reaction conditions (liquid‐to‐solid ratio of 10 g g^?1 and 120 mg H₂SO₄ g^?1 dry matter) 76.2% of the hemicellulose was hydrolyzed and the xylose and arabinose sugars were recovered with 67 and 97.8% efficiency, respectively. Copyright © 2005 Society of Chemical Industry     

Modeling thermodynamic properties of aqueous single‐solute and multi‐solute sugar solutions with PC‐SAFT

The Perturbed‐Chain Statistical Association Fluid Theory is applied to simultaneously describe various thermodynamic properties (solution density, osmotic coefficient, solubility) of aqueous solutions containing a monosaccharide or a disaccharide. The 13 sugars considered within this work are: glucose, fructose, fucose, xylose, maltose, mannitol, mannose, sorbitol, xylitol, galactose, lactose, trehalose, and sucrose. Four adjustable parameters (three pure‐sugar parameters and a k_ij between sugar and water that was allowed to depend linearly on temperature) were obtained from solution densities and osmotic coefficients of binary sugar/water solutions at 298.15 K available in literature. Using these parameters, the sugar solubility in water and in ethanol could be predicted satisfactorily. Further, osmotic coefficients and solubility in aqueous solutions containing two solutes (sugar/sugar, sugar/salt) were predicted (no additional k_ij parameters between the two solutes) reasonably. The model was also applied to predict the solubility of a sugar in a solvent mixture (e.g., water/ethanol) without additional fitting parameters. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4794–4805, 2013     

Characteristics of hemicelluloses obtained from sweet sorghum based on successive extractions

Hemicelluloses were successively extracted from sweet sorghum by hot water, dioxane, DMSO, and different concentrations of NaOH between 0.5% and 6.0%. The yields of the seven fractions together accounted for 88.6% of the original hemicelluloses. The obtained hemicellulosic subfractions were comprehensively investigated by both destructive methods such as alkaline nitrobenzene oxidation and acid hydrolysis and nondestructive techniques such as gel permeation chromatography, Fourier‐transform infrared, ¹³C‐nuclear magnetic resonance, and 2D‐heteronuclear singular quantum correlation. Sugar composition studies showed that the water‐soluble polysaccharides consisted mainly of glucose, while xylose, arabinose, and glucuronic acid were the major sugars in other hemicellulosic fractions. It was found that the hemicelluloses from sweet sorghum were l‐ arabino‐(4‐O‐methyl‐d‐ glucurono)‐xylans. Comparison with the hemicellulosic fractions dissolved by the alkali treatment, the hemicellulosic fraction extracted by DMSO had lower molecular weight. In addition, it was also found that the hemicelluloses prepared by dioxane and DMSO were more branched since that they had higher nonxylose/xylose ratios than those extracted by the alkali treatment, which were more linear and contained higher amounts xylose. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42790.     

Probing the Role of Chirality in Phospholipid Membranes

Nucleotides, amino acids, sugars, and lipids are almost ubiquitously homochiral within individual cells on Earth. While oligonucleotides and proteins exist as one natural chirality throughout the tree of life, two stereoisomers of phospholipids have separately emerged in archaea and bacteria, an evolutionary divergence known as “the lipid divide”. Within this review, we focus on the emergence of phospholipid homochirality and compare the stability of synthetic homochiral and heterochiral membranes in vitro. We discuss chemical probes designed to study the stereospecific interactions of lipid membranes in vitro. Overall, we aim to highlight studies that help elucidate the determinants of stereospecific interactions between lipids, peptides, and small molecule ligands. Continued work in understanding the drivers of favorable interactions between chiral molecules and biological membranes will lead to the design of increasingly selective chemical tools for bioorthogonal labeling of lipid membranes and safer membrane-associating pharmaceuticals.     

Statistical optimization of hydrolysis process for banana peels using cellulolytic and pectinolytic enzymes

Dried and ground banana peels (BP) were pretreated and hydrolyzed using a combination of cellulolytic and pectinolytic enzymes. Central composite design (CCD) was used to optimize cellulase, β-glucosidase and pectinase concentrations and hydrolysis time for production of glucose and reducing sugars. Design expert software was used to analyze and evaluate the data. The interactions between filter paper cellulase and β-glucosidase concentrations were statistically significant at a 95% confidence level in production of glucose and reducing sugars from BP. The validation experiment was carried out with cellulase, β-glucosidase and pectinase at 8 FPU/g cellulose, 15 IU/g cellulose and 66 IU/g pectin, respectively, for 15 h in a laboratory fermenter. The glucose and reducing sugars concentrations of 28.2 and 48 g/l, respectively, obtained through the validation experiment were higher than the theoretical values for glucose and reducing sugars predicted by the software. Glucose, galactose, arabinose, xylose and galacturonic acid concentrations increased with time, but a significant increase in fructose concentration was not observed. Process optimization also led to about 40% savings in hydrolysis time, indicating scale-up potential for the process.     

Enhanced microbial oil production by activated sludge microorganisms via co‐fermentation of glucose and xylose

The co‐fermentation of glucose and xylose by activated sludge microorganisms for the production of microbial oils for use as biodiesel feedstock was investigated. Various carbon sources at initial concentration of 60 g/L and C:N ratio 70:1 were investigated: xylose, glucose, and 2:1 and 1:2 (by mass) glucose/xylose mixtures. Oil accumulation ranged between 12 to 22% CDW, the highest of which was obtained when xylose was the sole substrate used. Kinetic modeling of the fermentation data showed that specific growth and oil accumulation rates were similar in all substrate types and the lipid coefficient ranged from 0.02 to 0.06 g/g of sugar consumed. The fatty acid methyl ester yield and composition of the lipids showed their suitability for conversion to biodiesel. Based on the results, lignocellulose sugars could be used as fermentation substrates by activated sludge microorganisms for enhancing the oil content of sewage sludge for its use as a sustainable biofuel feedstock source. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4036–4044, 2013