The rotorfermentor. II. Application to ethanol fermentation.

The kinetics of microbial growth and product formation are described as applied to the high cell concentration scheme of the rotorfermentor. A bench scale pilot plant was designed and built in order to demonstrate the operational feasibility of the rotorfermentor. The fermentation of glucose to ethanol by Saccharomyces cerevisiae ATCC 4126 was used. When the rotorfermentor was used with a glucose feed concentration of 104 g/liter almost 100% glucose utilization was obtained and the ethanol productivity rate was 27.3 g ethanol/liter hr which was found to be about 10 times greater than the ethanol productivity obtained from an ordinary continuous stirred tank (CST) fermentor. The ethanol experimental results obtained from the rotorfermentor and an ordinary CST fermentor were used as a basis to assess the economic feasibility of the rotorfermentor. The economics of an industrial scale ordinary CST fermentor with and without cell recycle is compared with a rotorfermentor unit for the same ethanol production throughput. For the process conditions considered in this case, calculations showed that the rotorfermentor may replace both a CST fermentor and cell centrifuge resulting in lower capital equipment costs and lower power consumption requirements.     

Determination of the volumetric mass transfer coefficient (k(L)a) using the dynamic "gas out-gas in" method: Analysis of errors caused by dissolved oxygen probes

There are many dynamic methods for measuring the volumetric mass transfer coefficient. The "gas out-gas in" method can directly determine the volumetric mass transfer coefficient in a bioreactor system and provide estimates of the volumetric microbial oxygen uptake rate and the average oxygen saturation concentration at the gas-liquid interface. The errors on these parameters are large if the dissolved oxygen probe response time is not considered. For reliable measurements, deconvolution of the oxygen probe measurements must be made. (c) 1995 John Wiley & Sons, Inc.     

Measurement of Gd-DTPA diffusion through PVA hydrogel using a novel magnetic resonance imaging method.

Polyvinyl alcohol-cryogel (PVA-C) is a hydrogel that is an excellent tissue mimic. In order to characterize mass transfer in this material, as well as to demonstrate in principle the ability to noninvasively measure solute diffusion in tissue, we measured the diffusion coefficient of the magnetic resonance (MR) contrast agent gadolinium diethylene triaminopentaacetic acid (Gd-DTPA) through PVA-C using a clinical MR imager. The method involved filling thick-walled rectangular PVA-C "cups" with known concentrations of Gd-DTPA solutions. Then by using a fast inversion recovery spin echo MR imaging protocol, a signal "null" contour was created in the MR image that corresponded to a second, known concentration of Gd-DTPA. By collecting a series of MR images through the PVA-C wall as a function of time, the displacement of this second known isoconcentration contour could be tracked. Application of Fick's second law of diffusion yielded the diffusion coefficient. Seven separate experiments were performed using various combinations of initial concentrations of Gd-DTPA within the PVA-C cups (3.2, 25.6, or 125 mM) and tracked isoconcentrations contours (0.096, 0.182, or 0.435 mM Gd-DTPA). The experimental results and the predictions of Fick's law were in excellent agreement. The diffusivity of Gd-DTPA through 10% PVA hydrogel was found to be (2.6 +/- 0.04) x 10(-10) m(2)/s (mean +/- s.e.m.). Separate permeability studies showed that the diffusion coefficient of Gd-DTPA through this hydrogel did not change with an applied pressure of up to 7.1 kPa. Accurate measurements could be made within 30 min if suitable Gd-DTPA concentrations were selected. Due to the excellent repeatability and fast data acquisition time, this technique is very promising for future in vivo studies of species transport in tissue.     

Stage-specific regulation of programmed cell death during oogenesis of the medfly Ceratitis capitata (Diptera, Tephritidae)

In the present study, we describe novel features of programmed cell death in developing egg chambers occurring during mid- and late-oogenesis of the medfly Ceratitis capitata. During mid-oogenesis, the spontaneously degenerated egg chambers exhibit typical characteristics of apoptotic cell death. Their nurse cells contain fragmented DNA and fragmented actin, as revealed by TUNEL assay and immunolabelling, respectively. In vitro caspase activity assays and immunostaining procedures demonstrated that the atretic egg chambers acquired high levels of caspase activity. Distinct features of autophagic cell death were also observed during C. capitata mid-oogenesis, as revealed by the monodansylcadaverine staining approach and ultrastructural examination performed by transmission electron microscopy. Additionally, atretic egg chambers exhibit an upregulation of lysosomal proteases, as demonstrated by a procathepsin L immunolabelling procedure. At the late stages of C. capitata oogenesis, apoptosis and autophagy coexist, manifesting cell death features that are similar to the ones mentioned above, being also chaperoned by the involvement of an altered cytochrome c conformational display. We propose that apoptosis and autophagy operate synergistically during C. capitata oogenesis for a more efficient elimination of the degenerated nurse cells and abnormal egg chambers.     

Stochastic Simulation of Biomolecular Networks in Dynamic Environments

Simulation of biomolecular networks is now indispensable for studying biological systems, from small reaction networks to large ensembles of cells. Here we present a novel approach for stochastic simulation of networks embedded in the dynamic environment of the cell and its surroundings. We thus sample trajectories of the stochastic process described by the chemical master equation with time-varying propensities. A comparative analysis shows that existing approaches can either fail dramatically, or else can impose impractical computational burdens due to numerical integration of reaction propensities, especially when cell ensembles are studied. Here we introduce the Extrande method which, given a simulated time course of dynamic network inputs, provides a conditionally exact and several orders-of-magnitude faster simulation solution. The new approach makes it feasible to demonstrate—using decision-making by a large population of quorum sensing bacteria—that robustness to fluctuations from upstream signaling places strong constraints on the design of networks determining cell fate. Our approach has the potential to significantly advance both understanding of molecular systems biology and design of synthetic circuits.     

Mass Transfer Characteristics of Immobilized Cells Used in Fermentation Processes

ABSTRACT:?

There is great commercial interest in using immobilized cells for fermented beverage processes. The process advantages offered by immobilized cells are numerous, but an understanding of the mass transfer characteristics of a given system is needed in order to achieve efficient processes and high quality products. This is especially important in the food and beverage industry where fermentation products contribute to the flavor and aroma of the final product. The fundamental principles of mass transfer in immobilized cell systems are covered in this review. An overview of the current research efforts focused on external and internal mass transfer characteristics of immobilized cells used in fermentation processes is presented. Methods for measuring substrate diffusivities within immobilization matrices and areas requiring further research are discussed.     

Cellular Localization and Characterization of Cytosolic Binding Partners for Gla Domain-containing Proteins PRRG4 and PRRG2

The genes encoding a family of proteins termed proline-rich γ-carboxyglutamic acid (PRRG) proteins were identified and characterized more than a decade ago, but their functions remain unknown. These novel membrane proteins have an extracellular γ-carboxyglutamic acid (Gla) protein domain and cytosolic WW binding motifs. We screened WW domain arrays for cytosolic binding partners for PRRG4 and identified novel protein-protein interactions for the protein. We also uncovered a new WW binding motif in PRRG4 that is essential for these newly found protein-protein interactions. Several of the PRRG-interacting proteins we identified are essential for a variety of physiologic processes. Our findings indicate possible novel and previously unidentified functions for PRRG proteins.     

Programmed cell death of follicular epithelium during the late developmental stages of oogenesis in the fruit flies Bactrocera oleae and Ceratitis capitata (Diptera, Tephritidae) is mediated by autophagy

In the present study, we describe the features of programmed cell death of ovarian follicle cells, occurring during the late developmental stages of oogenesis in the olive fruit fly, Bactrocera oleae and the medfly, Ceratitis capitata. During stage 14, the follicle cells contain autophagic vacuoles, and they do not exhibit caspase activity in all parts of the egg chamber. Their nuclei are characterized by condensed chromatin, accompanied with high- but not low-molecular weight DNA fragmentation events exclusively detected in distinct cells of the anterior pole. These data argue for the presence of an autophagy-mediated cell death program in the ovarian follicle cell layer in both species. The above results are likely associated with the abundant phagocytosis observed at the entry of the lateral oviducts, where numerous cell bodies are massively engulfed by epithelial cells. We strongly believe that during the termination of the above Dipteran oogenesis, an efficient mechanism of absorption of the degenerated follicle cells is selectively activated, in order to prevent the blockage of the ovarioles and thus robustly support the physiological completion of the ovulation process.     

Production and surface-active properties of microbial surfactants

A new source of surface-active compounds produced by microbes was investigated. These biologically derived surfactants (biosurfactants) were found to be extracellular products of two newly isolated Corynebacterium species, which were gorwn on kerosene (Imperial Oil No.9). Batch-growth kinetic studies were carried out in a 14 liter fermentor and the production of biosurfactants was found to be cell growth associated. The surface tension of the whole microbial broth was reduced to a minimum of about 30 dyn/cm, as compared with the surface tension for distilled water of 72 dyn/cm. The crude biosurfactants were recovered from the cell-free broth, freeze-dried, redissolved in water, and their surface-active properties were studied. The biosurfactants reported here were found to be nontoxic and their ability to lower the surface tension of water was found to be comparable to that of sodium dodecylbenzene sulfonate, common commercial synthetic surfactant.