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排序方式: 共有71条查询结果,搜索用时 156 毫秒
41.
Mariana P. Hanga Junaid Ali Panagiota Moutsatsou Fritz A. de la Raga Christopher J. Hewitt Alvin Nienow Ivan Wall 《Biotechnology and bioengineering》2020,117(10):3029-3039
Traditional farm-based products based on livestock are one of the main contributors to greenhouse gas emissions. Cultivated meat is an alternative that mimics animal meat, being produced in a bioreactor under controlled conditions rather than through the slaughtering of animals. The first step in the production of cultivated meat is the generation of sufficient reserves of starting cells. In this study, bovine adipose-derived stem cells (bASCs) were used as starting cells due to their ability to differentiate towards both fat and muscle, two cell types found in meat. A bioprocess for the expansion of these cells on microcarriers in spinner flasks was developed. Different cell seeding densities (1,500, 3,000, and 6,000 cells/cm2) and feeding strategies (80%, 65%, 50%, and combined 80%/50% medium exchanges) were investigated. Cell characterization was assessed pre- and postbioprocessing to ensure that bioprocessing did not negatively affect bASC quality. The best growth was obtained with the lowest cell seeding density (1,500 cells/cm2) with an 80% medium exchange performed (p < .0001) which yielded a 28-fold expansion. The ability to differentiate towards adipogenic, osteogenic, and chondrogenic lineages was retained postbioprocessing and no significant difference (p > .5) was found in clonogenicity pre- or postbioprocessing in any of the feeding regimes tested. 相似文献
42.
Expansion,harvest and cryopreservation of human mesenchymal stem cells in a serum‐free microcarrier process 下载免费PDF全文
Thomas R. J. Heathman Veronica A. M. Glyn Andrew Picken Qasim A. Rafiq Karen Coopman Alvin W. Nienow Bo Kara Christopher J. Hewitt 《Biotechnology and bioengineering》2015,112(8):1696-1707
43.
A. Carl Whittington Tatyana E. Nienow Christi L. Whittington Timothy J. Fort Theresa J. Grove 《PloS one》2012,7(11)
Calsequestrins (CSQ) are high capacity, medium affinity, calcium-binding proteins present in the sarcoplasmic reticulum (SR) of cardiac and skeletal muscles. CSQ sequesters Ca2+ during muscle relaxation and increases the Ca2+-storage capacity of the SR. Mammalian CSQ has been well studied as a model of human disease, but little is known about the environmental adaptation of CSQ isoforms from poikilothermic organisms. The mummichog, Fundulus heteroclitus, is an intertidal fish that experiences significant daily and seasonal environmental fluctuations and is an interesting study system for investigations of adaptation at the protein level. We determined the full-length coding sequence of a CSQ isoform from skeletal muscle of F. heteroclitus (FCSQ) and characterized the function and structure of this CSQ. The dissociation constant (Kd) of FCSQ is relatively insensitive to changes in temperature and pH, thus indicating that FCSQ is a eurytolerant protein. We identified and characterized a highly conserved salt bridge network in FCSQ that stabilizes the formation of front-to-front dimers, a process critical to CSQ function. The functional profile of FCSQ correlates with the natural history of F. heteroclitus suggesting that the eurytolerant function of FCSQ may be adaptive. 相似文献
44.
For the first time a laboratory-scale two-compartment system was used to investigate the effects of pH fluctuations consequent to large scales of operation on microorganisms. pH fluctuations can develop in production-scale fermenters as a consequence of the combined effects of poor mixing and adding concentrated reagents at the liquid surface for control of the bulk pH. Bacillus subtilis was used as a model culture since in addition to its sensitivity to dissolved oxygen levels, the production of the metabolites, acetoin and 2,3-butanediol, is sensitive to pH values between 6.5 and 7.2. The scale-down model consisted of a stirred tank reactor (STR) and a recycle loop containing a plug flow reactor (PFR), with the pH in the stirred tank being maintained at 6.5 by addition of alkali in the loop. Different residence times in the loop simulated the exposure time of fluid elements to high values of pH in the vicinity of the addition point in large bioreactors and tracer experiments were performed to characterise the residence time distribution in it. Since the culture was sensitive to dissolved oxygen, for each experiment with pH control by adding base into the PFR, equivalent experiments were conducted with pH control by addition of base into the STR, thus ensuring that any dissolved oxygen effects were common to both types of experiments. The present study indicates that although biomass concentration remained unaffected by pH variations, product formation was influenced by residence times in the PFR of 60 sec or longer. These changes in metabolism are thought to be linked to both the sensitivity of the acetoin and 2,3-butanediol-forming enzymes to pH and to the inducing effects of dissociated acetate on the acetolactate synthase enzyme. 相似文献
45.
Both k(L)a and k(L) measurements were carried out by an unsteady state technique at impeller speeds ranging from 1.6 to 5.8 s(-1) in a mechanically agitated animal cell culture vessel of working volume 1.5 L. Checks were made that the time constant of the oxygen electrode was negligible compared to the time for aeration and that the oxygen electrode reading was not a function of agitator speed in the range employed. The k(L) values by surface aeration of (1.18-3.54) x 10(-5) m/s and k(L)a values by sparged aeration of (2.8-8.5) x 10(-4) s(-1) were found. The former are in reasonable agreement with published experimental values and the latter in accord with values estimated from published correlations based on agitator power input and aeration rate. The fluids used were water, basal medium, and basal medium supplemented with 5% (v/v) foetal calf serum; for each of these, k(L) and k(L)a values were similar. However, the addition of silicone antifoam (6 PPM) reduced the k(L)a value by ca. 50%. 相似文献
46.
Aerated and unaerated power consumption and flow patterns in a 0.56 m diameter agitated vessel containing water with dual Rushton turbines have been studied. Under unaerated conditions with a liquid height-to-diameter ratio of 2, an impeller spacing of 2 to 3 times the impeller is required for each to draw an amount of power equal to a single impeller. For aerated conditions, if a similar spacing is used, equations for the flooding-loading transition and for power consumption for a single Rushton impeller can be extended relatively easily to dual systems. All results for this spacing are explained by reference to bulk flow patterns and gassed-filled cavity structures and the proportion of sparged gas flowing through the upper impeller is also estimated. Such a spacing is generally recommended since it maximizes the power draw and hence the potential for oxygen mass transfer. Data are presented for other spacings but the results do not fit in easily with single agitator studies because strong impeller-impeller flow pattern interactions occur. 相似文献
47.
L. G. Torres Prof. A. W. Nienow A. Sánchez Dr. E. Galindo 《Bioprocess and biosystems engineering》1993,9(6):231-237
Viscoelasticity has important implications in mass transfer and mixing processes. Previous studies regarding to the viscoelastic behaviour of xanthan solutions have been carried out with diluted solutions or they have not covered a wide range of polymer concentrations. In this study, it was shown that the first normal stress difference measured in fermentation broths is highly dependent on shear rate, and this viscoelastic level is modified by the heat treatment to which the broths are subjected as a postfermentative procedure. The viscoelasticity level is different for xanthan solutions prepared with products arising from different sources and for fermentation broths before the heat treatment, if compared with that measured in end-products. In general, the higher the polymer concentration, the higher the viscoelasticity (expressed as first normal stress difference or Weissenberg number). The addition of a biocide, the change in ionic strength and the addition of sucrose to the xanthan solutions, lead to significant changes in the first normal stress difference.List of Symbols
A Pa.Sb
constant in first normal stress difference power law (N
1=
)
-
b
constant in first normal stress difference power law (N
1=
)
-
c kg m–3
polymer concentration
-
K Nsn m–2
consistency index
-
N
1 Pa
first normal stress difference
-
n
flow behaviour index
-
Wi
Weissenberg number,N
1/
-
s–1
shear rate
-
Pa
shear stress
-
y Pa
Yield stress 相似文献
48.
Long-term productivity in the cryptoendolithic microbial community of the Ross Desert,Antarctica 总被引:6,自引:0,他引:6
Annual gross productivity of the lichen-dominated cryptoendolithic community was calculated from a computer analysis of photosynthetic response based on laboratory measurements of C02 exchange and three years (1985–1988) of field nanoclimate data. Photosynthetic optimum increased from –3 to 2°C between irradiance levels of 100 and 1500 mol photons m–2 s–1, while the upper compensation point rose from 1 to 17°C. The mean yearly total time available for metabolic activity (temperature above –10°C and moisture present) was 771.3 h for horizontal rock, 421.5 h for northeast-oriented sloped rock, and 1042.2 h for a small depression in horizontal rock (the characteristic site of occasional lichen apothecia). The calculated mean gross productivity value for a horizontal rock was 1215 mg C m–2 y–1, and net photosynthetic gain was 606 mg C m–2 y–1. Net ecosystem productivity (annual accretion of cellular biomass) estimated from long-term events amounted to only about 3 mg C m–2 y–1. The difference between these two values may represent the long-term metabolic costs of the frequent dehydration-rehydration and freezing-thawing cycles or of overwintering, and may account for the leaching of organic substances to the rock.The yearly gross productivity of the cryptoendolithic microbial community of the entire Ross Desert area was estimated at approximately 120,000–180,000 kg C. Of this, 600–900 kg C is in microbial biomass, and much of the rest is soluble compounds that leach into the rocks and possibly percolate to the valleys, providing a source of organic matter for lakes, rivers, and soils.
Offprint requests to: E. I. Friedmann. 相似文献
49.
N. Kioukia M. Al-Rubeai Z. Zhang A. N. Emery A. W. Nienow C. R. Thomas 《Biotechnology letters》1995,17(1):7-12
Summary Insect cells have been propagated in monolayers in T-flasks or in suspension culture in spinner flasks, the latter being conducted over a range of spinner speeds. In both configurations, the cells were also infected with either wild or recombinant -galactosidase baculovirus at MOI of 0.1, 1 and 10. The strength of both uninfected and infected cells was also measured by a micro-manipulation technique. No significant difference in growth rate was obtained between monolayer culture and suspension culture at the spinner rate which was optimum for growth. This optimum was quite sharp. At the lowest speeds cells settled, whilst above the optimum speed the spinner action led to significant cell damage. The maximum infectivity was obtained at this optimum speed which also gave maximum survival after infection. There were significant changes of cell survival and infection, even over relatively small changes of speed, and presumably energy dissipation rate. As changes in growth in turbine-agitated bioreactors have been shown to be much less, even when the energy inputs varied by two orders of magnitude, these findings throw doubt on the usefulness of spinner flasks for assessing shear sensitivity of cell lines. The percentage of infected cells and -galactosidase production were significantly lower in the monolayer culture compared to that in the suspension culture at MOI values below 10 pfu/cell. This difference is explained as being due to the reduced movement of released virus particles from infected to non-infected cells in the T-flasks. 相似文献
50.