Fermentation Kinetics and Continuous Process of L-Asparaginase Production

For the purpose of obtaining L-asparaginase in quantities from Erwinia aroideae, cell growth and enzyme formation were investigated in both batch and continuous fermentation. Using yeast extract as a growth-limiting substrate, the relationship between specific growth rate and substrate concentration was found to fit the Monod equation. The optimum temperature for enzyme production was 24 C, although cell growth was higher at 28 C. The enzyme yield reached its maximum of 4 IU/ml during the negative acceleration growth phase which occurs just prior to stationary growth. Compared to batch fermentations, the continuous fermentation process gave a lower enzyme yield except when the fermentation was conducted at a dilution rate of 0.1 hr(-1). The graphical method frequently used for prediction of continuous fermentation does not apply to L-asparaginase production by E. aroideae. The optimum temperature for enzyme production in continuous process was 24 C, which was the same as in batch process. Increasing the temperature from 24 to 28 C resulted in a 20% loss of enzyme yield.     

Saccharomyces cerevisiae Mutants Resistant to Catabolite Repression: Use in Cheese Whey Hydrolysate Fermentation

Mutants of an industrial-type strain of Saccharomyces cerevisiae which rapidly and completely fermented equimolar mixtures of glucose and galactose to ethanol were isolated. These mutants fell into two general phenotypic classes based upon their fermentation kinetics and enzyme induction patterns. One class apparently specifically effects the utilization of galactose and allows sequential utilization of first glucose and then galactose in an anaerobic fermentation. The second class of mutants was resistant to general catabolite repression and produced maltase, invertase, and galactokinase in the presence of repressive levels of glucose. These mutants were completely dominant and appear to represent an as yet undescribed class of mutant.     

Improved Bioreaction Kinetics for the Simulation of Continuous Ethanol Fermentation by Saccharomyces cerevisiae

A kinetic model for the production of ethanol by Saccharomyces cerevisiae has been developed from semiempirical analysis. The values for the parameters in this model were then determined by nonlinear multiple regression using the data of Bazua and Wilke ( 1977). The final equations were μ=0.427s(1-(p/101.6)^1.95)/(0.245+s), Y_X/p=0.291, and Y_X/s=0.152(1-p/302.3). This model was then used to simulate a continuous stirred tank fermentor (CSTF) and compared to other models using the same experimental data but different kinetics. The equations required to use these kinetics in a CSTF with recycle were then developed. From this simulation, it was found that, for a CSTF with recycle, the best configuration to operate is an external recycle, with a low bleed and recycle ratio.     

Mathematical Modelling of Anaerobic Reactors Treating Domestic Wastewater: Rational Criteria for Model Use

Anaerobic digestion modelling is an established method for assessing anaerobic wastewater treatment for design, systems analysis, operational analysis, and control. Anaerobic treatment of domestic wastewater is a relatively new, but rapidly maturing technology, especially in developing countries, where the combination of low cost, and moderate-good performance are particularly attractive. The key emerging technology is high-rate anaerobic treatment, particularly UASB reactors. Systems modelling can potentially offer a number of advantages to this field, and the key motivations for modelling have been identified as operational analysis, technology development, and model-based design. Design is particularly important, as it determines capital cost, a key motivation for implementers. Published modelling studies for anaerobic domestic sewage treatment are limited in number, but well directed at specific issues. Most have a low structural complexity, with first order kinetics, as compared to the more commonly used Monod kinetics. This review addresses the use of anaerobic models in general, application of models to domestic sewage systems, and evaluates future requirements for models that need to address the key motivations of operational analysis, technology development, and model-based design. For operational analysis and technology development, a complex model such as the ADM1 is recommended, with further extensions as required to address factors such as sulphate reduction. For design, the critical issSues are hydraulics and particles (i.e., biomass and solid substrate) modelling. Therefore, the kinetic structure should be relatively simple (at least two-step), but the hydraulic and particulate model should be relatively complex.     

Whey Fermentation by Anaerobiospirillum succiniciproducens for Production of a Succinate-Based Animal Feed Additive

Anaerobic fermentation processes for the production of a succinate-rich animal feed supplement from raw whey were investigated with batch, continuous, and variable-volume fed-batch cultures with Anaerobiospirillum succiniciproducens. The highest succinate yield, 90%, was obtained in a variable-volume fed-batch process in comparison to 80% yield in a batch cultivation mode. In continuous culture, succinate productivity was 3 g/liter/h, and the yield was 60%. Under conditions of excess CO₂, more than 90% of the whey-lactose was consumed, with an end product ratio of 4 succinate to 1 acetate. Under conditions of limited CO₂, lactose was only partially consumed and lactate was the major end product, with lower levels of ethanol, succinate, and acetate. When the succinic acid in this fermentation product was added to rumen fluid, it was completely consumed by a mixed rumen population and was 90% decarboxylated to propionate on a molar basis. The whey fermentation product formed under excess CO₂, which contained mainly organic acids and cells, could potentially be used as an animal feed supplement.     

A Continuous Correlated Beta Process Model for Genetic Ancestry in Admixed Populations

Admixture and recombination create populations and genomes with genetic ancestry from multiple source populations. Analyses of genetic ancestry in admixed populations are relevant for trait and disease mapping, studies of speciation, and conservation efforts. Consequently, many methods have been developed to infer genome-average ancestry and to deconvolute ancestry into continuous local ancestry blocks or tracts within individuals. Current methods for local ancestry inference perform well when admixture occurred recently or hybridization is ongoing, or when admixture occurred in the distant past such that local ancestry blocks have fixed in the admixed population. However, methods to infer local ancestry frequencies in isolated admixed populations still segregating for ancestry do not exist. In the current paper, I develop and test a continuous correlated beta process model to fill this analytical gap. The method explicitly models autocorrelations in ancestry frequencies at the population-level and uses discriminant analysis of SNP windows to take advantage of ancestry blocks within individuals. Analyses of simulated data sets show that the method is generally accurate such that ancestry frequency estimates exhibited low root-mean-square error and were highly correlated with the true values, particularly when large (±10 or ±20) SNP windows were used. Along these lines, the proposed method outperformed post hoc inference of ancestry frequencies from a traditional hidden Markov model (i.e., the linkage model in structure), particularly when admixture occurred more distantly in the past with little on-going gene flow or was followed by natural selection. The reliability and utility of the method was further assessed by analyzing genetic ancestry in an admixed human population (Uyghur) and three populations from a hybrid zone between Mus domesticus and M. musculus. Considerable variation in ancestry frequencies was detected within and among chromosomes in the Uyghur, with a large region of excess French ancestry harboring a gene with a known disease association. Similar variation was detected in the mouse hybrid zone, with notable constancy in regions of excess ancestry among admixed populations. By filling what has been an analytical gap, the proposed method should be a useful tool for many biologists. A computer program (popanc), written in C++, has been developed based on the proposed method and is available on-line at http://sourceforge.net/projects/popanc/.     

种群连续增长模型的学习过程

针对学生提出的问题“种群S型曲线为何在K／2时增长率最大”,通过多种渠道寻求答案,对“K／2”的实际应用提出了自己的见解。     

Process Optimization for the Production of Bio-functional Whey Protein Hydrolysates: Adopting Response Surface Methodology

Whey is a protein complex derived from milk, exhibit highest protein quality rating among other proteins, being touted as a functional food with number of health benefits. In the present investigation, whey proteins hydrolysates produced using trypsin enzyme to augment antioxidant activity and to assess angiotensin converting enzyme (ACE) inhibition activity. Hydrolysis parameters were standardized applying response surface methodology. The response antioxidant activity in terms of Trolox equivalent antioxidant capacity (TEAC) values was determined by radical scavenging assay method. Optimum conditions for maximum antioxidant activity were standardized at 88 °C of preheating, 7.3 pH, 0.05 enzymes to substrate ratio and hydrolysis was carried up to 8 h at 36.5 °C. Resulting peptide fractions obtained at 11.8 % of degree of hydrolysis displayed antioxidant capacity with TEAC values of 1.37 ± 0.12. The designed model found to be significant with R² value of 0.9972 for antioxidant activity and lack of fit test-as non significant, indicating that the optimized conditions were best suited. The hydrolysate further investigated for antihypertensive activity. The outcome indicate that to affect decrease in ACE inhibition activity 4,166.72 μg of native whey protein is required when compared to 229.96 μg of hydrolysates. These results indicate hydrolysate produced under these conditions could be an effective nutraceutical.     

A Mathematical Model of Interference for Use in Constructing Linkage Maps from Tetrad Data

In determining genetic map distances it is necessary to infer crossover frequencies from the ratios of recombinant and parental progeny. To do this accurately, in intervals where multiple crossovers may occur, a mathematical model of chiasma interference must be assumed when mapping in organisms displaying such interference. In Saccharomyces cerevisiae the model most frequently used is that of R.W. Barratt. An alternative to this model is presented. This new model is implemented using a microcomputer and standard numerical methods. It is demonstrated to fit ranked tetrad data from Saccharomyces more closely than the Barratt model and thus generates more accurate estimates of map distances when used with two-point data. A computer program implementing the model has been developed for use in calculating map distances from tetrad data in Saccharomyces.     

Synbiotic Fermentation for the Co‐Production of Lactic and Lactobionic Acids from Residual Dairy Whey

Besides its properties as an antioxidant, stabilizer, or acidifier, lactobionic acid has emerged as a potential prebiotic compound, raising the possibility of being included together with the probiotic microorganism Lactobacillus casei in novel functional fermented foods with synbiotic characteristics. Their manufacturing strategy could benefit from the recently implemented microbial synthesis of lactobionic acid by the strong producer Pseudomonas taetrolens, employing residual dairy whey as raw material. The phenomenon of amensalism established between Pseudomonas and Lactobacillus makes simultaneous fermentation unfeasible. A novel sequential process has been developed in which L. casei is inoculated in a second step. Its ability to utilize lactobionic acid as a carbon and energy source was previously tested. Experimental results showed the capacity of L. casei to work efficiently on the residual substrate fermented by P. taetrolens, producing lactic acid by degrading the remaining lactose, with a lactic acid yield on substrate and productivity of 0.95 g g^?1 and 0.20 g L^?1 h^?1, respectively. Lactobionic acid was barely consumed in this complex growth medium, thus ensuring its presence in the resulting fermented product. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1250–1256, 2017     

Membrane-Integrated Fermentation System for Improving the Optical Purity of D-Lactic Acid Produced during Continuous Fermentation

This report describes the production of highly optically pure D-lactic acid by the continuous fermentation of Sporolactobacillus laevolacticus and S. inulinus, using a membrane-integrated fermentation (MFR) system. The optical purity of D-lactic acid produced by the continuous fermentation system was greater than that produced by batch fermentation; the maximum value for the optical purity of D-lactic acid reached 99.8% enantiomeric excess by continuous fermentation when S. leavolacticus was used. The volumetric productivity of the optically pure D-lactic acid was about 12 g/L/h, this being approximately 11-fold higher than that obtained by batch fermentation. An enzymatic analysis indicated that both S. laevolacticus and S. inulinus could convert L-lactic acid to D-lactic acid by isomerization after the late-log phase. These results provide evidence for an effective bio-process to produce D-lactic acid of greater optical purity than has conventionally been achieved to date.     

静脉注射吸毒人群HIV／AIDS数学模型分析

建立了四川省西昌市静脉注射吸毒人群HIV／AIDS传播的数学模型,给出了模型的理论分析和数值模拟结果．通过必要的分析,给出了各类平衡点的存在性和稳定性,系统的一致持续生存,以及基本再生数的数学表达式和具体取值．揭示了该静注人群中的HIV／AIDS有进一步蔓延的趋势,但如果采取适当的干预措施,该静注人群中HIV／AIDS流行可得到有效的控制．     

A Mathematical Model for Evolution and SETI

Darwinian evolution theory may be regarded as a part of SETI theory in that the factor f_l in the Drake equation represents the fraction of planets suitable for life on which life actually arose. In this paper we firstly provide a statistical generalization of the Drake equation where the factor f_l is shown to follow the lognormal probability distribution. This lognormal distribution is a consequence of the Central Limit Theorem (CLT) of Statistics, stating that the product of a number of independent random variables whose probability densities are unknown and independent of each other approached the lognormal distribution when the number of factors increased to infinity. In addition we show that the exponential growth of the number of species typical of Darwinian Evolution may be regarded as the geometric locus of the peaks of a one-parameter family of lognormal distributions (b-lognormals) constrained between the time axis and the exponential growth curve. Finally, since each b-lognormal distribution in the family may in turn be regarded as the product of a large number (actually “an infinity”) of independent lognormal probability distributions, the mathematical way is paved to further cast Darwinian Evolution into a mathematical theory in agreement with both its typical exponential growth in the number of living species and the Statistical Drake Equation.     

Microbial Ecophysiology of Whey Biomethanation: Characterization of Bacterial Trophic Populations and Prevalent Species in Continuous Culture

The organization and species composition of bacterial trophic groups associated with lactose biomethanation were investigated in a whey-processing chemostat by enumeration, isolation, and general characterization studies. The bacteria were spatially organized as free-living forms and as self-immobilized forms appearing in flocs. Three dominant bacterial trophic group populations were present (in most probable number per milliliter) whose species numbers varied with the substrate consumed: hydrolytic, 10¹⁰; acetogenic, 10⁷ to 10¹⁰; and methanogenic, 10⁶ to 10⁹. The three prevalent species utilizing lactose were identified as Leuconostoc mesenteroides, Klebsiella oxytoca, and Clostridium butyricum. Clostridium propionicum and Desulfovibrio vulgaris were the dominant lactate-consuming, hydrogen-producing acetogenic bacteria, while D. vulgaris was the only significant ethanol-degrading species. Methanosarcina barkeri and Methanothrix soehngenii were identified as the dominant acetate-utilizing methanogens, and Methanobacterium formicicum was the prevalent hydrogen-utilizing methanogen. A microbial food chain is proposed for lactose biomethanation that comprises multiple species in three different groups, with the major hydrogen-producing acetogen being a sulfate-reducing species, D. vulgaris, which functioned in the absence of significant levels of environmental sulfate.     

Parabiotic Chamber for Organ Cultures: Improved Model

A modified parabiotic chamber for organ cultures is described. It consists of a modified organ culture dish, glass cover slip, a cylinder of semipermeable membrane, and a stainless-steel mesh filter support. Silicone and agar seals were used. Diffusion occurred rapidly and with consistent rates at 37 C when a ratio of 5:2 reservoir to inner chamber volume was used. The device is simple to construct and assemble and allows for continuous observation while maintaining a large surface area available for diffusion. The volumes of the reservoir, inner chamber, and agar base can be varied, and the chamber may be used with a wide variety of cell and organ culture systems.     

Use of Tenckhoff Catheter for Peritoneal Dialysis in Terminal Renal Failure

Over a period of 33 months a total of 2,146 peritoneal dialyses were carried out by means of indwelling Tenckhoff catheters in 65 patients suffering from terminal renal failure. The patients were maintained on peritoneal dialysis for periods varying from two weeks to 13 months. Treatment over long periods was possible in only a few cases. Infection and clotting, which tended to limit the functional life of the catheters, was reduced by rigid asepsis and by adding heparin to the dialysate. The Tenckhoff catheter was found to be valuable for peritoneal dialysis as a short-term measure, especially in patients in whom haemodialysis was not immediately feasible, in borderline cases when kidney function was not too seriously impaired, and as an alternative to haemodialysis when that was interrupted by complications.     

A Laboratory Model of a Prebiotic, Spontaneous, and Continuous Enantiomeric Enrichment Process

Construction and operation of a laboratory model, which combines the lately discovered enantioenrichment method of the author (2007) with the sun-powered evaporative pumping process of Hsu and Siegenthaler (Sedimentology 12:11–25 1969), is described. The model operated continuously for 120 days before it was intentionally shut down, even though it could have continued. During that time it raised the enantiomeric excess of the test material by a factor of 3.6. Implications of these results on the origin of biohomochirality are discussed.