Development of a phenomenological modeling approach for prediction of growth and xanthan gum production using Xanthomonas campestris

An unstructured kinetic model for xanthan production is described and fitted to experimental data obtained in a stirred batch reactor. The culture medium was composed of several nitrogen sources (soybean hydrolysates, ammonium and nitrate salts) consumed sequentially. The model proposed is able to describe this sequential consumption of nitrogen sources, the consumption of inorganic phosphate and carbon, the evolution of biomass, and production of xanthan. The parameter estimation has been performed by fitting the kinetic model in differential form to experimental data. Runs of the model for simulating xanthan gum production as a function of the initial concentration of inorganic phosphate have shown the positive effect of phosphate limitation on xanthan yield, though diminishing rates of production. The model was used to predict the kinetic parameters for a medium containing a 2-fold lower initial phosphate concentration. When tested experimentally, the measured fermentation parameters were in close agreement with the predicted model values, demonstrating the validity of the model.     

Recombinant antibodies against subcellular fractions used to track endogenous Golgi protein dynamics in vivo

Generation of specific antibodies against enriched subcellular fractions is a powerful strategy to identify and characterize cellular components. We show that recombinant antibodies can be selected in vitro by phage display against complex subcellular fractions, namely microtubule-binding proteins and Golgi stacks. This technique has allowed us to overcome many limitations of the classical animal-based approach and generate cell biology-compliant antibodies. In addition, we show that intracellular expression of GFP-tagged recombinant antibodies can reveal the dynamics of endogenous proteins in vivo . Endogenous Giantin is very static and outlines the Golgi in living cells. It accumulates neither onto Golgi-derived tubules upon Brefeldin A treatment before Golgi disappearance, nor onto de novo formed Golgi mini-stacks upon microtubule depolymerization, and remains instead on the 'old' pericentriolar Golgi. This suggests that, in contrast to other Golgi matrix proteins, endogenous Giantin is very stably associated with the Golgi and does not efficiently recycle to the ER. Altogether, we show that the antibody phage display technique represents an efficient alternative to rapidly generate versatile antibodies that represent new tools to study protein function.     

Human keratinocytes in culture exhibit no response when exposed to short duration, low amplitude, high frequency (900 MHz) electromagnetic fields in a reverberation chamber

We exposed normal human epidermal keratinocytes to short duration, high frequency, and low amplitude electromagnetic fields, similar to that used by mobile phone technologies. We paid particular attention to the control of the characteristics of the electromagnetic environment generated within a mode stirred reverberation chamber (statistical homogeneity and isotropy of the field and SAR distribution). Two non‐thermal exposure conditions were tested on the epidermal cells: 10‐min exposure with a field amplitude of 8 V/m, and 30 min with 41 V/m. Corresponding specific absorption rates ranged from 2.6 to 73 mW/kg (continuous wave, 900 MHz carrier frequency). We collected RNA from cells subjected to these conditions and used it for a large‐scale microarray screening of over 47000 human genes. Under these conditions, exposure of keratinocytes to the electromagnetic field had little effect; only 20 genes displayed significant modulation. The expression ratios were very small (close to 1.5‐fold change), and none of them were shared by the two tested conditions. Furthermore, those assayed using polymerase chain reaction did not display significant expression modulation (overall mean of the exposed samples: 1.20 ± 0.18). In conclusion, the data presented here show that cultured keratinocytes are not significantly affected by EMF exposure. Bioelectromagnetics 32:302–311, 2011. © 2010 Wiley‐Liss, Inc.     

Genetic analysis shows low levels of hybridization between African wildcats (Felis silvestris lybica) and domestic cats (F. s. catus) in South Africa

Hybridization between domestic and wild animals is a major concern for biodiversity conservation, and as habitats become increasingly fragmented, conserving biodiversity at all levels, including genetic, becomes increasingly important. Except for tropical forests and true deserts, African wildcats occur across the African continent; however, almost no work has been carried out to assess its genetic status and extent of hybridization with domestic cats. For example, in South Africa it has been argued that the long‐term viability of maintaining pure wildcat populations lies in large protected areas only, isolated from human populations. Two of the largest protected areas in Africa, the Kgalagadi Transfrontier and Kruger National Parks, as well as the size of South Africa and range of landscape uses, provide a model situation to assess how habitat fragmentation and heterogeneity influences the genetic purity of African wildcats. Using population genetic and home range data, we examined the genetic purity of African wildcats and their suspected hybrids across South Africa, including areas within and outside of protected areas. Overall, we found African wildcat populations to be genetically relatively pure, but instances of hybridization and a significant relationship between the genetic distinctiveness (purity) of wildcats and human population pressure were evident. The genetically purest African wildcats were found in the Kgalagadi Transfrontier Park, while samples from around Kruger National Park showed cause for concern, especially combined with the substantial human population density along the park's boundary. While African wildcat populations in South Africa generally appear to be genetically pure, with low levels of hybridization, our genetic data do suggest that protected areas may play an important role in maintaining genetic purity by reducing the likelihood of contact with domestic cats. We suggest that approaches such as corridors between protected areas are unlikely to remain effective for wildcat conservation, as the proximity to human settlements around these areas is projected to increase the wild/domestic animal interface. Thus, large, isolated protected areas will become increasingly important for wildcat conservation and efforts need to be made to prevent introduction of domestic cats into these areas.     

A new role for PGRP-S (Tag7) in immune defense: lymphocyte migration is induced by a chemoattractant complex of Tag7 with Mts1

PGRP-S (Tag7) is an innate immunity protein involved in the antimicrobial defense systems, both in insects and in mammals. We have previously shown that Tag7 specifically interacts with several proteins, including Hsp70 and the calcium binding protein S100A4 (Mts1), providing a number of novel cellular functions. Here we show that Tag7–Mts1 complex causes chemotactic migration of lymphocytes, with NK cells being a preferred target. Cells of either innate immunity (neutrophils and monocytes) or acquired immunity (CD4⁺ and CD8⁺ lymphocytes) can produce this complex, which confirms the close connection between components of the 2 branches of immune response.     

Bemerkungen über die Achsenbestimmung des Froschembryo und die Gastrulation des Froscheies

Zusammenfassung Die Beobachtungen F.Kopsch's an Amphibieneiern bieten keine Veranlassung dar, an der Auffassung, dass bei der ganz normalen, also typischen Entwickelung des Froscheies die erste Furche zugleich die Medianebene des Embryo darstellt und dass die zweite Furche den reellen Embryo annähernd transversal in Kopf- und Schwanzhälfte theilt, etwas zu ändern. Das Medullarrohr wird daher normaler Weise nicht bloß von den sog. vorderen (cephalen), sondern zu einem wesentlichen Theil auch von dem Materiale der hinteren (caudalen) beiden der vier ersten Blastomeren des Eies gebildet, wenn auch in den letzteren unter differenzirendem Einfluss der ersteren.Die Dorsalseite des Froschembryo wird auf der Unterseite der Blastula und zwar unter bilateraler Überwachsung mit Konkrescenz angelegt. (Bei einigen anderen Amphibien scheint nachEycleshymer undKing ein erheblicher Theil des Gehirns etwas weiter oben und, wie beim Frosche der quere Gehirnwulst, ohne Konkrescenz gebildet zu werden.) Kopsch's Schlusssatz: »Beim Ei von Rana fusca bestehen keine strengen, sondern nur innerhalb gewisser Breite schwankende Beziehungen zwischen der ersten Furchungsebene und der Medianebene des Embryo«, gilt nur für nicht ganz normale und für direkt abnorme Verhältnisse und stammt in dieser Hinsicht bereits vonPflüger, mir,Born, Hertwig u. A. (s. Nr. 5, pag. 327, 331, 349).Die durchKopsch's photographische Aufnahme gastrulirender Amphibieneier erkennbar gewordenen Zellenverschiebungen lassen sich gleich wie die von vielen Autoren wesentlich übereinstimmend beobachteten Bewegungen der vorderen Urmundlippen um 60–80°, der hinteren Urmundlippen um 30–40° auf verschiedene Weise deuten. Die vonKopsch vertretene Ableitung der Entstehung seines Befundes stellt nur das eine Extrem des danach denkbaren Geschehens dar, die meinige repräsentirt das andere Extrem. Außer diesen sind unendlich viele zwischen beiden gelegene, graduell verschiedene Deutungen möglich.Von allen diesen hat diejenige Deutung am meisten Wahrscheinlichkeit für sich, welche mit den anderen bezüglichen Beobachtungen an derselben Species am besten in Einklang zu bringen ist. Das ist bei den gegenwärtig von Rana vorliegenden Thatsachen die von mir vertretene Deutung; während die Auffassung, dass der reelle Embryo senkrecht in der Blastula stehe, dass also die zweite Furche frontale Richtung habe und das Material für die dorsale und ventrale Hälfte des Embryo scheide, in Widerspruch steht: erstens zu der fast wagerechten Lage des Embryo mit dem Rücken nach unten auf dem Eie bei Zwangslage, zweitens zu der primären Entstehung typischer vorderer Halbbildungen nach Abtödtung der hinteren beiden der vier ersten Furchungszellen, drittens mit der wagerechten statt senkrechten Stellung der Medullarwülste bei Pressung der Eier zwischen senkrechten Platten und viertens mit den übereinstimmenden Ergebnissen der Anstichversuche an Rana von mir, T. H.Morgan undBertacchini.     

Spatial partitioning of the soil water resource between grass and shrub components in a West African humid savanna

Most savanna water balance models assume water partitioning between grasses and shrubs in a two-layer hypothesis, but this hypothesis has not been tested for humid savanna environments. Spatial partitioning of soil water between grasses and shrubs was investigated in a West African humid savanna by comparing the isotopic composition (oxygen-18 and deuterium) of soil water and plant stem water during rainy and dry conditions. Both grass and shrub species acquire most of their water from the top soil layer during both rainy and dry periods. A shift of water uptake pattern towards deeper horizons was observed only at the end of the dry season after shrub defoliation. The mean depth of water uptake, as determined by the isotopic signature of stem water, was consistent with grass and shrub root profiles and with changes in soil water content profiles as surveyed by a neutron probe. This provides evidence for potentially strong competition between shrubs and grasses for soil water in these humid savannas. Limited nutrient availability may explain these competitive interactions. These results enhance our understanding of shrub-grass interactions, and will contribute to models of ecosystem functioning in humid savannas.     

Plasminogen activator and collagenase production by cultured capillary endothelial cells

Cultured bovine capillary endothelial (BCE) cells produce low levels of collagenolytic activity and significant amounts of the serine protease plasminogen activator (PA). When grown in the presence of nanomolar quantities of the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA), BCE cells produced 5-15 times more collagenolytic activity and 2-10 times more PA than untreated cells. The enhanced production of these enzymes was dependent on the dose of TPA used, with maximal response at 10(-7) to 10(-8) M. Phorbol didecanoate (PDD), an analog of TPA which is an active tumor promoter, also increased protease production. 4-O-methyl-TPA and 4α-PDD, two analogs of TPA which are inactive as tumor promoters, had no effect on protease production. Increased PA and collagenase activities were detected within 7.5 and 19 h, respectively, after the addition of TPA. The TPA-stimulated BCE cells synthesized a urokinase-type PA and a typical vertebrate collagenase. BCE cells were compared with bovine aortic endothelial (BAE) cells and bovine embryonic skin (BES) fibroblasts with respect to their production of protease in response to TPA. Under normal growth conditions, low levels of collagenolyic activity were detected in the culture fluids from BCE, BAE, and BES cells. BCE cells produced 5-13 times the basal levels of collagenolytic activity in response to TPA, whereas BAE cells and BES fibroblasts showed a minimal response to TPA. Both BCE and BAE cells exhibited relatively high basal levels of PA, the production of which was stimulated approximately threefold by the addition of TPA. The observation that BCE cells and not BAE cells produced high levels of both PA and collagenase activities in response to TPA demonstrates a significant difference between these two types of endothelial cells and suggests that the enhanced detectable activities are a property unique to bovine capillary and microvessel and endothelial cells.