Investigation of the structure of two-phase flow fermentation model media in bubble-column bioreactors

Summary Electrical conductivity microprobes have been used to estimate the transverse variation of bubble size, local gas holdup and local specific gas/liquid interfacial area in bench scale bubble column bioreactors containing fermentation model media. Inserted O₂-electrodes and plane parallel windows alter the structure of the two phase flow. Even slight tilting of the column strongly influences the transverse profiles of the bubble size and local gas holdup. The larger bubbles are collected at the wall, where they can be redispersed. These observations open up new possibilities for the construction of bubble column bioreactors.     

Sequential 1H NMR assignments of kistrin, a potent platelet aggregation inhibitor and glycoprotein IIb-IIIa antagonist.

Sequence-specific nuclear magnetic resonances assignments have been obtained for the protons of kistrin. Kistrin is a small naturally occurring snake venom protein that inhibits platelet aggregation by blocking the interaction of fibrinogen with the membrane-bound glycoprotein IIb-IIIa (GP IIb-IIIa), a receptor from the integrin family. Kistrin has an Arg-Gly-Asp sequence which is believed to form an adhesion recognition sequence that is essential for activity. Therefore, the interaction between kistrin and GP IIb-IIIa may provide important information on the motif used by integrins to recognize their target proteins which bear RGD sequences. Kistrin consists of 68 residues and contains six intramolecular disulfide bonds. Although one-third of the amide protons are protected from exchange with the solvent, there appears to be little or no regular secondary structure. The large number of NOE's between residues separated by two and three positions in the sequence indicates that the protein contains a large number of tightly packed loops. Along with the sequential assignments, this paper also discusses the construction and use of computerized data bases for manipulating NMR results. A strategy for computer-assisted sequential resonance using these data bases is also presented.     

Liver cytosolic fatty acids binding proteins in rats and Psammomys obesus: modulation in diabetes

The effect of insulin on [3H]oleate binding to delipidated liver cytosolic proteins was studied in four groups of animals: untreated rats, streptozotocin induced diabetic rats, Psammomys obesus fed salt bush diet, and Psammomys obesus fed ordinary laboratory chow. The distribution of the protein bound [3H]oleate between low and high molecular weight cytosolic proteins in Psammomys differed from the distribution found in rats. Diet induced high insulin diabetes in Psammomys and streptozotocin induced low insulin diabetes in rats, modulated [3H]oleate binding in the same manner.     

Fusion of bacterial spheroplasts by electric fields

Spheroplasts of Escherichia coli or Salmonella typhimurium were found to fuse in an electric field. We employed the fusion method developed by Zimmermann and Scheurich (1981): Close membrane contact between cells is established by dielectrophoresis (formation of chains of cells by an a.c. field), then membrane fusion is induced by the application of short pulses of direct current. Under optimum conditions the fusion yield was routinely 90%. Fusable spheroplasts were obtained by first growing filamentous bacteria in the presence of cephalexin, then converting these to spheroplasts by the use of lysozyme. The fusion products were viable and regenerated to the regular bacterial form. Fusion of genetically different spheroplasts resulted in strains of bacteria possessing a combination of genetic markers. Fusion could not be achieved with spheroplasts obtained by growing the cells in the presence of penicillin or by using lysozyme on bacteria of usual size.     

The roles of abiotic factors, dispersal, and species interactions in structuring stream assemblages of black flies (Diptera: Simuliidae)

ABSTRACT: BACKGROUND: The patterns and drivers of species assemblages represent the core of community ecology.We focus on the assemblages of a single family of ubiquitous lotic insects, the Simuliidae(black flies), of which the larvae play a critical role in resource turnover in steams. We useMantel tests and null models to tease out the potential influence of abiotic stream conditions,species interactions, and dispersal on the assemblage patterns of larval black flies over twospatial scales (within and across ecoregions) and two seasons (spring and summer). RESULTS: When stream sites were considered across ecoregions in the spring, stream conditions anddispersal were correlated significantly with species similarity; however, within ecoregions inthe spring, dispersal was important only in the Piedmont and Sandhills and abiotic factorsonly in the Mountains. In contrast, results of the summer analyses within and acrossecoregions were congruent; assemblage similarity was significantly correlated with streamconditions both across and within ecoregions. Null models suggested that patterns of speciessegregation in the spring were consistent with a community structured by competition,whereas patterns in the summer were consistent with species assemblages influenced byabiotic factors. CONCLUSIONS: Species composition of black flies at streams sites is correlated with dispersal factors andstream conditions, but results vary over spatial and temporal scales. Communities of blackflies can be viewed within a metacommunity context; local assemblages are consistent withspecies sorting and mass effects. Given that black flies have a terrestrial stage, with femalesdeciding where to place the eggs, a full understanding of the processes that determine local aquatic assemblages will require integration of the dynamics of the aquatic immature stagesand the terrestrial adults.     

Polyol accumulation by two filamentous fungi grown at different concentrations of NaCl

The accumulation of polyols by Aspergillus niger (van Tiegh) strain S 1 and Penicillium chrysogenum (Thom) strain S 30 was followed during growth in media of different concentrations of NaCl. The major polyols found were glycerol, erythritol and mannitol. The total polyol pool increased in both organisms in response to raised salinity, and the proportion of glycerol and erythritol was markedly enhanced at high salinity.     

The human PDGF receptor α-subunit gene maps to chromosome 4 in close proximity to c-kit

Summary The gene encoding the -subunit of the human platelet-derived growth factor receptor (PDGFRA) maps to band q11–q12 of chromosome 4 by in situ hybridization, which was confirmed by Southern analysis of a Chinese hamster × human cell hybrid that retains only human chromosome 4.     

Protein synthesis during imaginal disc pattern regulation

We have examined the pattern of protein synthesis during wing disc pattern regulation. Although in vivo culture dramatically alters the pattern of abundant protein synthesis in wing discs, only one protein--RG38--changes specifically in response to pattern regulation. This polypeptide, previously identified as being nonuniformly distributed in wing and haltere discs, is synthesized in a graded distribution across the wing disc. During wing disc pattern regulation, it acts as a molecular marker for regeneration of particular wing disc regions. Thus, the rate of RG38 synthesis increases during regeneration (by fragments with initial low levels) with kinetics that parallel those for regeneration as scored by the presence of adult cuticular structures.