Microfiltration of yeast suspensions with self-cleaning spiral vortices: possibilities for a new membrane module design

A novel method of producing controlled vortices was used to reduce both concentration polarization and membrane fouling during microfiltration of Saccharomyces cerevisiae broth suspensions. The method involves flow around a curved channel at a sufficient rate so as to produce centrifugal instabilities (called Dean vortices). These vortices depolarize the build-up of suspended particles such as yeast cells at the membrane-solution interface and allow for increased membrane permeation rates. Various operating conditions under which such vortices effectively reduced cake build-up of suspended particles such as yeast cells at the membrane-solution interface and allow for increased membrane permeation rates. Various operating conditions under which such vortices effectively reduced cake build-up during microfiltration of 0 to 0.55 dry wt% yeast broth were investigated. Flux improvements of over 60% for 0.25 dry wt% yeast broth for flow with over that without Dean vortices were observed. This beneficial effect increased with increasing retentate flow rate and increasing transmembrane pressure and decreased with increasing concentration of suspended matter. Similar behavior was observed whether the cells were viable of killed. the improvement in flux in the presence over that in the absence of vortices correlated well with centrifugal force or azimuthal velocity squared. The relative cake resistances increased with reservoir yeast concentration. These values with vortices increased from 62% to 75% of that without vortices with increasing yeast concentration. The ratio of the cake thicknesses in the limiting case (at high feed concentration) was 3.25. These results suggest that self-cleaning spiral vortices could be effective in maintaining good and steady microfiltration performance with cell suspensions other than those tested. (c) 1995 John Wiley & Sons, Inc.     

球形红杆菌积累聚β-羟基链烷酸(PHA)的研究

通过对球形红杆菌(Rhodobacter sphaeroides)生长和积累聚卢-羟基链烷酸(PHA)条件的研究,确定采用两段培养法提高PHA的产量。第一阶段提供适合菌体生长的条件:以葡萄糖作碳源,尿素为氮源,光照微好氧培养。第二阶段则提供使菌体积累PHA的条件:补加乙酸钠厌氧光照培养。经两段培养后菌体PHA含量可占细胞干重的45％,PHA产量每升发酵液可达1.7g。     

标志技术在研究小皱蝽成虫种群特征中的应用

应用标志－释放－回收技术研究小皱蝽成虫的主要种群特征,结果如下：（１）成虫扩散的偏离度Ｋｕ＝２．４,为一阶峻开曲线;（２）分别用Ｐｅｔｅｒｓｏｎ和Ｊａｃｋｓｏｎ方法对种群蜜度进行了估计,结果表明,Ｊａｃｋｓｏｎ的方法较好;（３）雄虫平均寿命４０－４５,虫平均寿命１２０－１３０。天。     

Outgroup heteroduplex analysis using temperature gradient gel electrophoresis: high resolution, large scale, screening of DNA variation in the mitochondrial control region

The ability of DNA screening techniques such as Temperature Gradient Gel Electrophoresis (TGGE) and Heteroduplex Analysis to provide resolution approaching that provided by DNA sequencing for a fraction of the time, effort and expense point to them as the logical successor to allozyme electrophoresis for population genetics. Here we present a novel alternative to the standard TGGE/Heteroduplex Analysis protocol - Outgroup Heteroduplex Analysis (OHA). We assess this technique's sensitivity in comparison to previous screening approaches using a known hierarchy of sequence differences. Our data show that Outgroup Heteroduplex Analysis has greatly increased sensitivity for screening DNA variants from that of TGGE used alone and is easily applicable to large numbers of samples. Using this technique we can consistently detect differences of as small as one base change in a 433-base-pair fragment of Control Region mitochondrial DNA from Melomys cerbinipes (an Australian rodent). The approach should easily be extendable to nuclear loci and is not necessarily dependent on the use of a denaturing gradient When combined with a targeted sequencing effort, OHA provides a sensitive and simple means of obtaining allele/haplotype frequencies and their phylogenies for population and phylogeographic studies in molecular ecology.     

黄土丘陵沟壑区水平梯田改土培肥增产技术措施体系

黄土丘陵沟壑区水平梯田改土培肥增产技术措施体系刘东海赵廷宁（宁夏西吉县农业局７５６２００）（北京林业大学水土保持学院１０００８３）赵国杰（宁夏西吉县农业技术推广站７５６２００）ＴｅｃｈｎｉｑｕｅｓｏｆＳｏｉｌＩｍｐｒｏｖｅｍｅｎｔａｎｄＹｉｅｌｄＩｎ...     

Action of vasoactive intestinal peptide (VIP) on amphibian adrenocortical function,in vitro

Vasoactive intestinal peptide (VIP) is located in chromaffin cells of the frog adrenal gland and is able to stimulate corticosteroid secretion in amphibians. In the present study we have investigated the possible involvement of prostaglandins, microfilaments and calcium in the mechanism of action of VIP on frog adrenocortical tissue. Rana ridibunda interrenal dice were perifused with amphibian culture medium for more than 10 hours. Corticosterone and aldosterone concentrations were measured in the effluent perifusate using sensitive and specific radioimmunoassay methods. In the presence of indomethacin (5 μM), a specific blocker of prostaglandin biosynthesis, the spontaneous secretion of corticosteroids was markedly reduced (80%) but the stimulatory effect of VIP was not altered. The administration of the microfilament disrupting agent cytochalasin B (50 μM) inhibited both spontaneous and VIP-induced corticosteroid secretion. In the absence of calcium, the spontaneous level of corticosteroid was reduced to about 60% but VIP was still able to stimulate corticosteroid secretion. From these data we conclude that the integrity of the cytoskeleton is required for the secretory response of adrenocortical cells to VIP, whereas neither prostaglandins nor calcium are involved in VIP-induced adrenocortical stimulation.     

An immunoblotting technique for the detection of bound and secreted bacterial Fc receptors

A rapid semiquantitative procedure that enables bacteria to be screened for surface or secreted receptors for the Fc region of human IgG is described. Surface Fc receptors were detected by direct transfer of bacterial colonies to nitrocellulose by electroblotting and then probing with ¹²⁵I-labeled human IgG in the presence of a two fold molar excess of unlabeled F(ab′)₂fragments. The blots were exposed to X-ray film and the intensity of the resulting autoradiograph was a measure of surface Fc receptors expression. This procedure reliably distinguished Staphylococcus aureus strains which expressed different levels of surface Fc receptors. When applied to the study of group A streptococci, a number of Fc receptor-positive strains were identified. Unlike the homogeneous Fc receptor expression on individual colonies of the staphylococcal strains, a wide variation in the level of Fc receptor expression was observed within a given streptococcal strain. Group A streptococcal substrains which expressed high and low levels of surface Fc receptors could be isolated from replica plates.Secreted Fc receptors were measured by a simple modification of the blotting procedure in which the nitrocellulose was placed on the opposite side of the agar from the bacterial colonies. Secreted Fc receptors was electroblotted through the agar onto nitrocellulose and probed as described above. This approach readily detected nanogram quantities of secreted type I Fc receptor (protein A) from the Staphylococcus aureus Cowan strain. None of the group A streptococcal strains tested were found to secrete detectable quantities of Fc receptors.     

Preparation and discharge of secretion in the subcommissural organ of the rat

Summary The secretion of the subcommissural organ (SCO) of the rat was studied by means of immunocytochemistry at the electron-microscopic level with the use of (1) the polar embedding medium Lowicryl K4M at -30° C, (2) the protein A-gold technique, and (3) a rabbit antiserum against bovine Reissner's fiber (see Sterba et al. 1981).Two different substructures of the ependymal and the hypendymal SCO-cells display a positive immunocytochemical reaction: (1) sacs containing flocculent secretion, which originate from the granular endoplasmic reticulum, and (2) vacuoles filled with fine granular secretion, which are pinched off from the Golgi apparatus. The secretory material of the sacs and the vacuoles is discharged both (i) apically into the cerebrospinal fluid and (ii) basally into intercellular spaces of the SCO-hypendyma. The apically released secretion is condensed to a lamina-like formation, which more caudally assumes the form of Reissner's fiber. The route of the basally released secretion remains, however, vague. The periodically striated bodies, which were thought to be morphological mediators of the discharge of the secretion into the capillaries, are never labeled by gold particles.Supported by grants from the Ministry for Science and Technology of the German Democratic RepublicThe expert technical assistance of Mrs. B. Wolff, Mrs. S. Mehnert, Mrs. E. Siebert, Mrs. Ch. Schneider, and Mrs. I. Seifert is gratefully acknowledged