Studies on the respiration rate of free and immobilized cells of Cephalosporium acremonium in cephalosporin C production

Bioprocesses using filamentous fungi immobilized in inert supports present many advantages when compared to conventional free cell processes. However, assessment of the real advantages of the unconventional process demands a rigorous study of the limitations to diffusional mass transfer of the reagents, especially concerning oxygen. In this work, a comparative study was carried out on the cephalosporin C production process in defined medium containing glucose and sucrose as main carbon and energy sources, by free and immobilized cells of Cephalosporium acremonium ATCC 48272 in calcium alginate gel beads containing alumina. The effective diffusivity of oxygen through the gel beads and the effectiveness factors related to the respiration rate of the microorganism were determined experimentally. By applying Monod kinetics, the respiration kinetics parameters were experimentally determined in independent experiments in a complete production medium. The effectiveness factor experimental values presented good agreement with the theoretical values of the approximated zero‐order effectiveness factor, considering the dead core model. Furthermore, experimental results obtained with immobilized cells in a 1.7‐L tower bioreactor were compared with those obtained in 5‐L conventional fermentor with free cells. It could be concluded that it is possible to attain rather high production rates working with relatively large diameter gel beads (ca. 2.5 mm) and sucrose consumption‐based productivity was remarkably higher with immobilized cells, i.e., 0.33 gCPC/kg sucrose/h against 0.24 gCPC/kg sucrose/h in the aerated stirred tank bioreactor process. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 593–600, 1999.     

Effects of Light intensity on Photosynthetic Characteristics of Wheat Seedling

The contents of pigments and chlorophyll-protein complexes, fluorescence characteristics and electron transport rate were compared for wheat seedlings grown under different light intensities. Leaves of wheat seedlings grown under low-light intensity (2 klx) had lower chlorophyll and carotenoid contents on leaf area or fresh weight basis, a lower ratio of chlorophyll a/b, lower CPIa and CPI contents in photosynthetic membranes than those of wheat seedlings grown under high-light intensity (20 klx). However, the LHCP content in photosynthetic membranes was higher in the former. The kinetic studies of fluorescence induction showed that wheat seedlings grown under low-light intensity possessed a bigger photosynthetic unit, lower PSⅡ activity and lower efficiency of primary energy conversion than those grown under high-light intensity. Moreover. lower electron transport rate was found in the chloroplasts of the former.     

The rate of antigenic variation in fly-transmitted and syringe-passaged infections of Trypanosoma brucei

Rates of antigenic variation were measured in vivo in several populations of cloned lines of Trypanosoma brucei before and after cyclical transmission through tsetse flies. Two cloned lines were adapted for use in laboratory conditions by extensive syringe passaging and rates of antigenic switching/cell/generation were less than 3×10⁻⁶ and 1×10⁻⁴ in each line. Rates of switching were then determined after fly transmission of the first line and generated per capita rate values of greater than 2×10⁻³ in three of four populations examined. In the fourth population the switch rate was lower: less than 7×10⁻⁵ switches/cell/generation. These data show that rates of antigenic variation are several orders of magnitude lower in syringe-passaged lines, such as those routinely used in the majority of laboratory studies, compared with most recently fly-transmitted lines. They also show that the reduction in switching rate associated with syringe passaging is reversible and is thus unlikely to be caused by mutation.     

ChooseMaterials.pl，控制变量挑选实验材料的perl脚本

用Perl语言编写了一个脚本--ChooseMaterials．pl,通过计算两个材料特定某几列数据之间增加或减少的百分数水平,达到控制变量突出关键因子的作用,方便生物学工作者选取材料,做进一步的实验或分析。     

Ecological time-series analysis through structural modelling with latent constructs: concepts, methods and applications

Time-series analyses in ecology usually involve the use of autoregressive modelling through direct and/or delayed difference equations, which severely restricts the ability of the modeler to structure complex causal relationships within a multivariate frame. This is especially problematic in the field of population regulation, where the proximate and ultimate causes of fluctuations in population size have been hotly debated for decades. Here it is shown that this debate can benefit from the implementation of structural modelling with latent constructs (SEM) to time-series analysis in ecology. A nonparametric bootstrap scheme illustrates how this modelling approach can circumvent some problems posed by the climate-ecology interface. Stochastic Monte Carlo simulation is further used to assess the effects of increasing time-series length and different parameter estimation methods on the performance of several model fit indexes. Throughout, the advantages and limitations of the SEM method are highlighted.     

Variable selection for marginal longitudinal generalized linear models

Variable selection is an essential part of any statistical analysis and yet has been somewhat neglected in the context of longitudinal data analysis. In this article, we propose a generalized version of Mallows's C(p) (GC(p)) suitable for use with both parametric and nonparametric models. GC(p) provides an estimate of a measure of model's adequacy for prediction. We examine its performance with popular marginal longitudinal models (fitted using GEE) and contrast results with what is typically done in practice: variable selection based on Wald-type or score-type tests. An application to real data further demonstrates the merits of our approach while at the same time emphasizing some important robust features inherent to GC(p).     

Bayesian information criterion for censored survival models

We investigate the Bayesian Information Criterion (BIC) for variable selection in models for censored survival data. Kass and Wasserman (1995, Journal of the American Statistical Association 90, 928-934) showed that BIC provides a close approximation to the Bayes factor when a unit-information prior on the parameter space is used. We propose a revision of the penalty term in BIC so that it is defined in terms of the number of uncensored events instead of the number of observations. For a simple censored data model, this revision results in a better approximation to the exact Bayes factor based on a conjugate unit-information prior. In the Cox proportional hazards regression model, we propose defining BIC in terms of the maximized partial likelihood. Using the number of deaths rather than the number of individuals in the BIC penalty term corresponds to a more realistic prior on the parameter space and is shown to improve predictive performance for assessing stroke risk in the Cardiovascular Health Study.     

Locally adaptive function estimation for binary regression models

In this paper we present a nonparametric Bayesian approach for fitting unsmooth or highly oscillating functions in regression models with binary responses. The approach extends previous work by Lang et al. for Gaussian responses. Nonlinear functions are modelled by first or second order random walk priors with locally varying variances or smoothing parameters. Estimation is fully Bayesian and uses latent utility representations of binary regression models for efficient block sampling from the full conditionals of nonlinear functions.     

The iterated continuous prisoner's dilemma game cannot explain the evolution of interspecific mutualism in unstructured populations

The evolutionionary origin of inter- and intra-specific cooperation among non-related individuals has been a great challenge for biologists for decades. Recently, the continuous prisoner's dilemma game has been introduced to study this problem. In function of previous payoffs, individuals can change their cooperative investment iteratively in this model system. Killingback and Doebeli (Am. Nat. 160 (2002) 421-438) have shown analytically that intra-specific cooperation can emerge in this model system from originally non-cooperating individuals living in a non-structured population. However, it is also known from an earlier numerical work that inter-specific cooperation (mutualism) cannot evolve in a very similar model. The only difference here is that cooperation occurs among individuals of different species. Based on the model framework used by Killingback and Doebeli (2002), this Note proves analytically that mutualism indeed cannot emerge in this model system. Since numerical results have revealed that mutualism can evolve in this model system if individuals interact in a spatially structured manner, our work emphasizes indirectly the role of spatial structure of populations in the origin of mutualism.