Syntrophic interactions improve power production in formic acid fed MFCs operated with set anode potentials or fixed resistances

Formic acid is a highly energetic electron donor but it has previously resulted in low power densities in microbial fuel cells (MFCs). Three different set anode potentials (-0.30, -0.15, and +0.15 V; vs. a standard hydrogen electrode, SHE) were used to evaluate syntrophic interactions in bacterial communities for formic acid degradation relative to a non-controlled, high resistance system (1,000 Ω external resistance). No current was generated at -0.30 V, suggesting a lack of direct formic acid oxidation (standard reduction potential: -0.40 V). More positive potentials that allowed for acetic acid utilization all produced current, with the best performance at -0.15 V. The anode community in the -0.15 V reactor, based on 16S rDNA clone libraries, was 58% Geobacter sulfurreducens and 17% Acetobacterium, with lower proportions of these genera found in the other two MFCs. Acetic acid was detected in all MFCs suggesting that current generation by G. sulfurreducens was dependent on acetic acid production by Acetobacterium. When all MFCs were subsequently operated at an external resistance for maximum power production (100 Ω for MFCs originally set at -0.15 and +0.15 V; 150 Ω for the control), they produced similar power densities and exhibited the same midpoint potential of -0.15 V in first derivative cyclic voltammetry scans. All of the mixed communities converged to similar proportions of the two predominant genera (ca. 52% G. sulfurreducens and 22% Acetobacterium). These results show that syntrophic interactions can be enhanced through setting certain anode potentials, and that long-term performance produces stable and convergent communities.     

The structure of epidermal feet during their development

Epidermal cells in Calpodes and other insects form basal processes or feet that at first extend axially and later shorten at the same time as the larval segment shortens to the pupal shape. The feet grow into spaces at the surfaces of other cells to make a basal interlacing meshwork of cellular extensions that are combined mechanically by their desmosomal attachments to cell bodies above and to the basal lamina below. Microtubules and microfilaments are linked to these junctions by a reticular fibrous matrix. Gap junctions on the feet may couple cells that are several cell bodies removed from one another. The meshwork is also a sieve separating the hemolymph from the spaces between cells to form an intercellular compartment. Entry to the intercellular compartment is through the sieve made by the negatively charged basolateral cell surfaces that can prevent the entry of positively charged molecules such as cationic ferritin. As the cells become columnar, coincident with the metamorphic change in segment shape, the feet shorten and pack more densely together. At this time the basal lamina buckles axially as if responding to contraction of the feet. Segment shape change involves cell rearrangement and relative cell movement, necessitating the transient loss of plasma membrane plaque attachments to the cuticle apically and the loss of junctions laterally. Gap junctions involute in characteristic vacuoles. The metamorphic reduction in cell surface area coincides with the loss of basolateral membrane in smooth tubes and vesicles and the turnover of the apical surface in multivesicular bodies. New apical plasma membrane plaques and new lateral and basal junctions stabilize the cells in their pupal positions.     

软骨血管生成抑制因子抑制血管生成的研究

小牛气管软骨经盐酸胍抽提,丙酮分级沉淀,膜超滤,柱层析等步骤得到软骨血管生成抑制因子(cartilage angiogenesis inhibiting factor,CAIF).SDS-聚丙烯酰胺凝胶电泳显示CAIF由单一组分组成,分子量为27700.通过[ ³H]-TdR掺入,活细胞检测等方法测定CAIF对内皮细胞、Hela细胞、QGY7703细胞与小鼠骨髓细胞、人皮肤成纤维细胞等的DNA合成的影响,以及细胞毒作用.采用鸡胚绒毛尿囊膜实验测定CAIF对血管生成的抑制效应.结果显示:CAIF对内皮细胞产生强的抑制作用,对Hela细胞抑制很弱,对QGY7703细胞、小鼠骨髓细胞、人皮肤成纤维细胞均无抑制作用;对鸡胚绒毛尿囊膜的血管生成产生明显的抑制作用.提示CAIF能较特异地抑制血管生成,CAIF达到电泳纯,是专一性较强的血管生成抑制因子.     

Isolation and analysis of cell wall material from beeswing wheat bran (Triticum aestivum)

Cell wall material (CWM) isolated from beeswing wheat bran contains 66% carbohydrate, 12% Klason lignin, 6% protein and 4% ash. The relative proportions of sugars in the CWM are arabinose 34%, xylose 26%, galactose 2%, glucose 32% and uronic acid 6%. The uronic acid was shown to consist of glucuronic acid and its 4-O-Me analogue in the ratio 1.8:1. Partial acid hydrolysis of the CWM yielded neutral sugars and a uronic acid fraction. The latter was shown to contain Glc p A-(1→2)-Xyl p and Glc p A-(1→2)-O-Xyl p-(1→4)-Xyl p and their 4-O-Me substituted uronic acid analogues. Methylation analysis of the whole CWM and partially degraded methylated CWM revealed the nature of the constituent glycosidic linkages. From the combined evidence we infer that the major structural features of the non-cellulosic polysaccharides are a linear chain of xylopyranose units joined by (1→4)-linkages, and arabinofuranose, xylose, galactose (and uronic acid) end groups, which in at least some of the polysaccharides, are attached directly by (1→2)- and/or (1→3)-linkages to the xylan chain. The CWM has been fractionated by successive extractions with water at 80°, 0.2 M (NH₄)₂C₂O₄ at 80°, Na chlorite/HOAc at 70°, 0.2 M (NH₄)₂C₂O₄ at 80°, 1 M and 4 M KOH, and the neutral sugar composition of the fractions determined. It is concluded from these and other experiments that the CWM contains two main types of polysaccharides, the arabinoxylans and cellulosic polymers, and that phenolic ester linkages play a role in holding them together.     

Plate-Induced tumors of BALB/3T3 cells exhibiting foci of differentiation into pericytes,chondrocytes, and fibroblasts

The BALB/3T3 clone A31 mouse embryo cell line has been used by many investigators as a model “normal” “fibroblast” line for a variety of in vitro studies. It has been shown, however, that these cells are not “normal” because they will produce tumors within 2–4 months if 3 × 10⁴ cells are implanted subcutaneously in BALB/c mice attached to 0.2 × 5 × 10-mm plastic plates. Previous studies also suggested that these cells were not fibroblasts because they gave rise to tumors with the characteristics of vascular endothelium not fibroblasts. We now report that BALB/3T3 (clone A31), BALB/3T3-T, a proadipocyte subclone of clone A31 cells, and six recent subclones of BALB/3T3-T cells show additional differentiation patterns when tumors derived by implantation of these cells attached to plastic plates are examined. Differentiation into pericytes, chondrocytes, and fibroblasts was observed. We conclude that the BALB/3T3 clone A31 cell line and related lines are multipotent mesenchymal cells which are capable of differentiation into a variety of cell types.     

Active cell membrane mechanisms involved in the exclusion of RH 123 allow distinction between normal and tumoral cells

Human cell lines derived from three epithelial carcinomas (CaSki, HeLa, SiHa), one B lymphoma (BL60), one promyelocytic (HL60), one monocytic (U937) leukemia, one chronic myelogenous leukemia (sensitive K562S; multichemoresistant K562R) and normal human skin fibroblasts were compared for their capacity of staining with rhodamine 123 (Rh 123) and their kinetics of dye exclusion. Cells were exposed for 30 min to 10 g/ml of Rh 123 in culture medium; fluorescence intensity was measured by flow cytometry immediately or 1, 2, 3 and 4 h after staining. The highest fluorescence intensity was observed in carcinoma cell lines; there was no incorporation in multichemoresistant K562R cells. Exclusion of Rh 123 was evaluated from 0 to 4 h, both by flow cytometry and by fluorimetry. Fluorescence intensity measured by flow cytometry decreased slightly in carcinoma and leukemia cells and rapidly in fibroblasts. In all cell lines Rh 123 exclusion was inhibited by 40 mol/L verapamil and 5 mmol/L probenecid. Thus, incorporation and exclusion of Rh 123 allows distinction between normal and tumoral cells; moreover, inhibition of exclusion by verapamil and probenecid favors the involvement of active cell membrane mechanisms in the exclusion process.Abbreviations PBS phosphate-buffered saline - Rh 123 rhodamine 123     

小鼠胚胎与子宫单层上皮细胞共培养的研究

本文报道建立了小鼠胚胎与小鼠子宫单层上皮细胞体外共培养系统。结果揭示;小鼠胚胎与 子宫单层上皮细胞共培养可以促进胚胎的发育、粘附和扩展;如果培养液中加入 ３、６７ × １０－６ｍｏｌ／Ｌ １７β－雌二醇,可以显著提高胚胎在共培养系统中的发育率、粘附率和扩展率。以上结果表明：小鼠 胚胎与小鼠子宫单层上皮细胞共培养系统是研究胚泡着床机理较理想的研究手段。     

Engineering challenges in high density cell culture systems

High density cell culture systems offer the advantage of production of bio-pharmaceuticals in compact bioreactors with high volumetric production rates; however, these systems are difficult to design and operate. First of all, the cells have to be retained in the bioreactor by physical means during perfusion. The design of the cell retention is the key to performance of high density cell culture systems. Oxygenation and media design are also important for maximizing the cell number. In high density perfusion reactors, variable cell density, and hence the metabolic demand, require constant adjustment of perfusion rates. The use of cell specific perfusion rate (CSPR) control provides a constant environment to the cells resulting in consistent production. On-line measurement of cell density and metabolic activities can be used for the estimation of cell densities and the control of CSPR. Issues related to mass transfer and mixing become more important at high cell densities. Due to the difference in mass transfer coefficients for oxygen and CO₂, a significant accumulation of dissolved CO₂ is experienced with silicone tubing aeration. Also, mixing is observed to decrease at high densities. Base addition, if not properly done, could result in localized cell lysis and poor culture performance. Non-uniform mixing in reactors promotes the heterogeneity of the culture. Cell aggregation results in segregation of the cells within different mixing zones. This paper discusses these issues and makes recommendations for further development of high density cell culture bioreactors.