Evaluation of two unstructured mathematical models for the penicillin G fedbatch fermentation

The mathematical model for the penicillin G fed-batch fermentation proposed by Heijnen et al. (1979) is compared with the model of Bajpai & Reuß (1980). Although the general structure of these models is similar, the difference in metabolic assumptions and specific growth and production kinetics results in a completely different behaviour towards product optimization. A detailed analysis of both models reveals some physical and biochemical shortcomings. It is shown that it is impossible to make a reliable estimation of the model parameters, only using experimental data of simple constant glucose feed rate fermentations with low initial substrate amount. However, it is demonstrated that some model parameters might be key factors in concluding whether or not altering the substrate feeding strategy has an important influence on the final amount of product.It is illustrated that feeding strategy optimization studies can be a tool in designing experiments for parameter estimation purposes.     

叶片叶肉结构对环境光强的适应及对光合作用的影响

本文利用Kubelka-Munk理论描述了平行光在叶片内的吸收和散射,同时利用叶片分层光合作用非直角双曲线光反应模型,给出了整张叶片光合作用计算式。最后利用优化理论阐明了叶片叶肉分化成光合特性具有明显差异的栅栏组织和海绵组织可能是对叶片内光梯度的一种适应;同时证明了叶片叶肉在一定环境光强下存在一个最佳的栅栏组织和海绵组织比例,并且这个比例随环境光强增大而增大,这最佳比例也受叶肉组织光合特性差异的影响。     

Subjective experiences associated with thermal biofeedback treatment of hypertension

Reports of subjective experiences of 73 hypertensive patients who were treated with thermal biofeedback for hand warming were obtained over 16 treatment sessions. Most of the differential responding in subjective report occurred in the first 5 sessions. Differences in reports of throbbing were associated with medication status during treatment (presence of sympatholytic antihypertensive agent). From 4 to 9% of patients report negative subjective experiences at any one session. When short-term clinical successes (either elimination of medication or reduction of BP) were compared with short-term failures, it was found that successes reported more warmth, more likelihood of falling asleep, and more dreamlike experiences. The latter were more likely to occur suddenly for the successes. Correlational analyses revealed consistent positive associations between reports of warmth and relaxation with highest temperature achieved in the session and consistent negative associations between experiencing physical sensations and degree of temperature change within the session.This research was supported in part by grants from NHLBI, HL-27622 and HL-31189.     

Primary culture of normal rat mammary epithelial cells within a basement membrane matrix. II. Functional differentiation under serum-free conditions

Summary A serum-free primary culture system is described which allows normal rat mammary epithelial cells (RMECs) embedded within a reconstituted basement membrane to undergo extensive growth and functional differentiation as detected by synthesis and secretion of the milk products casein and lipid. RMECs isolated from mammary glands of immature virgin rats were seeded within an extracellular matrix preparation derived from the Engelbreth-Holm-Swarm sarcoma and cultured in a serum-free medium consisting of Dulbecco's modified Eagle's medium-F12 containing insulin, prolactin, progesterone, hydrocortisone, epidermal growth factor, bovine serum albumin, transferrin, and ascorbic acid. Casein synthesis and secretion were documented at the electron microscopic level as well as by an enzyme-linked immunosorbent assay (ELISA) assay using a polyclonal antibody against total rat caseins. Numerous secretory vesicles with casein micelles were noted near the apical surface of the RMECs, and secreted casein was observed in the lumen. These ultrastructural data were confirmed by the ELISA assay which showed that microgram amounts of casein per well were synthesized by the RMECs and that the amount of casein increased with time in culture. Using immunoblot analysis it was demonstrated that the full complement of casein proteins was synthesized. In addition to casein protein, β-casein mRNA levels were shown to increase with time. Synthesized lipid was detected at both the light and electron microscopic levels. Phase contrast photomicrographs demonstrated extensive intracellular lipid accumulation within the ductal and lobuloalveolarlike colonies, and at the electron micrograph level, lipid droplets were predominantly localized near the apical surface of the RMECs. The lipid nature of these droplets was verified by oil red O staining. Results from this study demonstrate that RMECs from immature virgin rats proliferate extensively and rapidly develop the capacity to synthesize and secrete casein and lipid when grown within a reconstituted basement membrane under defined serum-free conditions. This unique system should thus serve as an excellent model in which the regulation of mammary development and gene expression can be investigated. This work was supported by grants CA 33240 and CA 35641 and by core grant CA 24538 from the National Institutes of Health, Bethesda, MD.     

Discovery of isolated patches ofIcerya purchasi byRodolia cardinalis: A field study

The discovery of isolated patches of prey by the natural enemies of the cottony-cushion scaleIcerya purchasi Maskell was tested in the field on potted plants ofAcacia baileyana and citrus between November and February in South Australia. The survival of scales to adults in patches in the 4 fortnightly releases (cohort sets) was not significantly different between location-1 (under anAcacia tree harbouring scales and its natural enemies) and location-2 (about 500 m away from the nearest host plant of the scale). The temporal distribution of mortality in the scale cohorts was described by the Weibull model. The proportion of scales surviving at the 2 locations (on the 3^rd & 6^th fornight) was not significantly different suggesting that the total effect of all the mortality factors on the scales at the 2 locations was the same. The trends in prey patches destroyed in time could be explained from the period of activity of the natural enemies in the field.Rodolia cardinalis (Mulsant) had discovered the prey patches within a fortnight of the release of scale crawlers. The results substantiate earlier reports thatRodolia can find and destroy isolated scale colonies.      

Nucleotide sequence and presumed secondary structure of the 28S rRNA of pea aphid implication for diversification of insect rRNA

Determination of the entire nucleotide sequence of the aphid 28S ribosomal RNA gene (28S rDNA) revealed that it is 4,147 by in length with a G + C content of 60.3%. Based on the nucleotide sequence, we constructed a presumed secondary-structure model of the aphid 28S rRNA which indicated that the aphid 28S rRNA is characterized by the length and high G + C content of its variable regions. The G + C content of the aphid's variable regions was much higher than that of the entire sequence of the 28S rRNA, which formed a striking contrast to those ofDrosophila with the G + C content much lower than the entire 28S molecule. In this respect, the aphid 28S rRNA somewhat resembled those of vertebrates. This is the third report of a complete large-subunit rRNA sequence from an arthropod, and the first 28S rRNA sequence for a nondipterous insect. Correspondence to: H. Ishikawa     

External Protons Enhance the Activity of the Hyperpolarization-activated K Channels in Guard Cell Protoplasts of Vicia faba

Hyperpolarization-activated K channels (K _H channels) in the plasmalemma of guard cells operate at apoplastic pH range of 5 to over 7. Using patch clamp in a whole-cell mode, we characterized the effect of varying the external pH between 4.4–8.1 on the activity of the K _H channels in isolated guard cell protoplasts from Vicia faba leaves. Acidification from pH 5.5 to 4.4 increased the macroscopic conductance of the K _H channels by 30–150% while alkalinization from pH 5.5 to 8.1 decreased it only by roughly 15%. The voltage-independent maximum cell conductance, increased by ∼60% between pH 8.1 and 4.4 with an apparent pK _a of 5.3, most likely owing to the increased availability of channels. Voltage-dependent gating was affected only between pH 5.5 and 4.4. Acidification in this range shifted the voltage-dependent open probability by over 10 mV. We interpret this shift as an increase of the electrical field sensed by the gating subunits caused by the protonation of external negative surface charges. Within the framework of a surface charge model the mean spacing of these charges was ∼30 ? and their apparent dissociation constant was 10^−4.6. The overall voltage sensitivity of gating was not altered by pH changes. In a subgroup of protoplasts analyzed within the framework of a Closed-Closed-Open model, the effect of protons on gating was limited to shifting of the voltage-dependence of all four transition rate constants. Received: 26 April 1996/Revised: 29 June 1996     

MATING SYSTEM AND ASYMMETRIC HYBRIDIZATION IN A MIXED STAND OF EUROPEAN OAKS

The sessile (Quercus petraea [Matt.] Liebl.) and pedunculate (Quercus robur L.) oaks are two closely related species having a wide sympatric distribution over Europe. Under natural conditions, they frequently form mixed forests, where hybridization is suspected to occur. In this paper, two different approaches have been applied to the study of the mating system and the interspecific gene flow in a mixed stand formed by the two species. The mating systems of both species have been studied separately by means of the mixed-mating model. The relative contribution of the parental species to the progenies have been estimated with two different methods. The first uses the admixture model. The second is an extension of the mixed-mating model and subdivides the outcrossing rate into intra- and interspecific components. The two species were almost completely outcrossing. This high level of outcrossing and interspecific gene flow could play an important role in the maintenance of the genetic diversity in these long-lived forest tree species. The contribution of the sessile oak to the pedunculate oak progenies varied from 17% to 48%. In contrast, ovules of sessile oak trees appear to be preferentially fertilized by other extreme sessile genotypes. We suggest that interspecific and directional gene flow was responsible for such patterns. Pedunculate oak is considered as a pioneer species and is progressively replaced by sessile oak. Our present findings add a further genetic component to this succession scheme, suggesting that unidirectional gene flow reinforces succession between the two species.     

Mathematical model for the ecosystem response of Lake Ladoga to phosphorus loading

The ecosystem response model described in this paper combines an ecosystem model and a three-dimensional circulation model of Lake Ladoga developed earlier by the authors. The ecosystem model describes the process of Lake Ladoga eutrophication, and its biological submodel describes changes in the phyto- and zooplankton. In the earlier model version, lake circulation was determined using a two-dimensional hydrodynamical model which was not completely adequate. The present model allows calculation of the distributions of phyto- and zooplankton and mineral phosphorus and nitrogen. One of its main advantages is that reliable computations of the ecosystem dynamics over an extended period of time are possible. The response of the ecosystem to different levels of phosphorus pollution loading and to weather conditions is studied.     

Mathematical modelling of runoff and material transport from drainage areas into recipient water bodies

This paper describes a set of mathematical models to calculate runoff, soil erosion and chemical substance yields for drainage areas. The models represent different degrees of complexity and details of describing hydrological and hydrochemical processes. The availability of initial information and the requirements of the task determine the choice of a model for each particular case. These models have been written as PC/AT programs, to enable their use by a wide range of specialists. The models have been tested in different physical and geographical conditions, e.g. in some small watersheds on the Karelian Isthmus, west of Lake Ladoga, and in experimental catchment areas located in the Valdai Hills area in the southern part of Lake Ladoga drainage area. In further applications the drainage area models have been combined with models of the recipient water body, to obtain a single model of a watershed-lake system. The results of tests have proved that the models can be used for evaluation, simulation and forecasting of the processes of rainfall and snowmelt runoff, infiltration, evaporation, water erosion and pollutant wash-off from drainage areas.