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951.
952.
Assessment of Reductive Acetogenesis with Indigenous Ruminal Bacterium Populations and Acetitomaculum ruminis
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Tricia D. le Van Joseph A. Robinson John Ralph Richard C. Greening Walter J. Smolenski Jane A. Z. Leedle Daniel M. Schaefer 《Applied microbiology》1998,64(9):3429-3436
The objective of this study was to evaluate the role of reductive acetogenesis as an alternative H2 disposal mechanism in the rumen. H2/CO2-supported acetogenic ruminal bacteria were enumerated by using a selective inhibitor of methanogenesis, 2-bromoethanesulfonic acid (BES). Acetogenic bacteria ranged in density from 2.5 × 105 cells/ml in beef cows fed a high-forage diet to 75 cells/ml in finishing steers fed a high-grain diet. Negligible endogenous acetogenic activity was demonstrated in incubations containing ruminal contents, NaH13CO3, and 100% H2 gas phase since [U-13C]acetate, as measured by mass spectroscopy, did not accumulate. Enhancement of acetogenesis was observed in these incubations when methanogenesis was inhibited by BES and/or by the addition of an axenic culture of the rumen acetogen Acetitomaculum ruminis 190A4 (107 CFU/ml). To assess the relative importance of population density and/or H2 concentration for reductive acetogenesis in ruminal contents, incubations as described above were performed under a 100% N2 gas phase. Both selective inhibition of methanogenesis and A. ruminis 190A4 fortification (>105 CFU/ml) were necessary for the detection of reductive acetogenesis under H2-limiting conditions. Under these conditions, H2 accumulated to 4,800 ppm. In contrast, H2 accumulated to 400 ppm in incubations with active methanogenesis (without BES). These H2 concentrations correlated well with the pure culture H2 threshold concentrations determined for A. ruminis 190A4 (3,830 ppm) and the ruminal methanogen 10-16B (126 ppm). The data demonstrate that ruminal methanogenic bacteria limited reductive acetogenesis by lowering the H2 partial pressure below the level necessary for H2 utilization by A. ruminis 190A4. 相似文献
953.
954.
Loss of the Plasma Membrane-Bound Protein Gas1p in Saccharomyces cerevisiae Results in the Release of β1,3-Glucan into the Medium and Induces a Compensation Mechanism To Ensure Cell Wall Integrity
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![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Arthur F. J. Ram Johan C. Kapteyn Roy C. Montijn L. Heleen P. Caro Jeroen E. Douwes Walter Baginsky Paul Mazur Herman van den Ende Frans M. Klis 《Journal of bacteriology》1998,180(6):1418-1424
Deletion of GAS1/GGP1/CWH52 results in a lower β-glucan content of the cell wall and swollen, more spherical cells (L. Popolo, M. Vai, E. Gatti, S. Porello, P. Bonfante, R. Balestrini, and L. Alberghina, J. Bacteriol. 175:1879–1885, 1993; A. F. J. Ram, S. S. C. Brekelmans, L. J. W. M. Oehlen, and F. M. Klis, FEBS Lett. 358:165–170, 1995). We show here that gas1Δ cells release β1,3-glucan into the medium. Western analysis of the medium proteins with β1,3-glucan- and β1,6-glucan-specific antibodies showed further that at least some of the released β1,3-glucan was linked to protein as part of a β1,3-glucan–β1,6-glucan–protein complex. These data indicate that Gas1p might play a role in the retention of β1,3-glucan and/or β-glucosylated proteins. Interestingly, the defective incorporation of β1,3-glucan in the cell wall was accompanied by an increase in chitin and mannan content in the cell wall, an enhanced expression of cell wall protein 1 (Cwp1p), and an increase in β1,3-glucan synthase activity, probably caused by the induced expression of Fks2p. It is proposed that the cell wall weakening caused by the loss of Gas1p induces a set of compensatory reactions to ensure cell integrity. 相似文献
955.
Catherin Niemann Volker Brinkmann Eva Spitzer Guido Hartmann Martin Sachs Helga Naundorf Walter Birchmeier 《The Journal of cell biology》1998,143(2):533-545
We have established a cell culture system that reproduces morphogenic processes in the developing mammary gland. EpH4 mouse mammary epithelial cells cultured in matrigel form branched tubules in the presence of hepatocyte growth factor/scatter factor (HGF/SF), the ligand of the c-met tyrosine kinase receptor. In contrast, alveolar structures are formed in the presence of neuregulin, a ligand of c-erbB tyrosine kinase receptors. These distinct morphogenic responses can also be observed with selected human mammary carcinoma tissue in explant culture. HGF/SF-induced branching was abrogated by the PI3 kinase inhibitors wortmannin and . In contrast, neuregulin- induced alveolar morphogenesis was inhibited by the MAPK kinase inhibitor PD98059. The c-met–mediated response could also be evoked by transfection of a c-met specific substrate, Gab1, which can activate the PI3 kinase pathway. An activated hybrid receptor that contained the intracellular domain of c-erbB2 receptor suffices to induce alveolar morphogenesis, and was observed in the presence of tyrosine residues Y1028, Y1144, Y1201, and Y1226/27 in the substrate-binding domain of c-erbB2. Our data demonstrate that c-met and c-erbB2 signaling elicit distinct morphogenic programs in mammary epithelial cells: formation of branched tubules relies on a pathway involving PI3 kinase, whereas alveolar morphogenesis requires MAPK kinase. LY294002相似文献
956.
Eugene Chudin Alan Garfinkel James Weiss Walter Karplus Boris Kogan 《Progress in biophysics and molecular biology》1998,69(2-3):225-236
Computer simulation using Luo-Rudy I1 model of ventricular myocyte showed that intracellular calcium dynamics become irregular in case of high rate stimulation. This causes the transition from stationary to nonstationary spiral wave and its breakup in 2D model of cardiac tissue. Obtained results suggest how ventricular fibrillation may occur due to the abnormalities of intracellular calcium dynamics. The short review of existing cardiac cell models with calcium dynamics is presented. 相似文献
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