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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Bioprocess and biosystems engineering 1 (1986), S. 29-41 
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Tissue cells are known to be sensitive to mechanical stresses imposed on them by agitation in bioreactors. The amount of agitation provided in a microcarrier or suspension bioreactor should be only enough to provide an effective homogeneity. Three distinct flow regions can be identified in the reactor: bulk turbulent flow, bulk laminar flow, and boundary-layer flows. Possible mechanisms of cell damage are examined by analyzing the motion of microcarriers or free cells relative to the surrounding fluid, to each other, and to moving or stationary solid surfaces. The primary mechanisms of cell damage appear to result from (a) direct interaction between microcarriers and turbulent eddies, (b) collisions between microcarriers in turbulent flow, and (c) collisions against the impeller or other stationary surfaces. If the smallest eddies of turbulent flow are of the same size as the microcarrier beads, they may cause high shear stresses on the cells. Eddies the size of the average interbead spacing may cause bead-bead collisions which damage cells. The severity of the collisions increases when the eddies are also of the same size as the beads. Bead size and the interbead distance are virtually equal in typical microcarrier suspensions. Impeller collisions occur when the beads cannot avoid the impeller leading edge as it advances through the liquid. The implications of the results of this analysis on the design and operation of tissue culture bioreactors are also discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 149 (1988), S. 214-219 
    ISSN: 1432-072X
    Keywords: Protonmotive force ; Active transport ; RuMP-type methylotrophs ; δpH ; δΨ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Formaldehyde accumulation ratios ([14CH2O]i/[14CH2O]o) as high as 12-fold were measured in anaerobic, CH3OH-energized, whole cell suspensions of the ribulose monophosphate (RuMP)-type methylotrophic strain T15. Uptake kinetics were extremely rapid, enabling the attainment of equilibrium in only 10–30 s. Transport appears to be energy-dependent and associated with the protonmotive force (pmf). Anaerobic incubation with 5 μM carbonyl p-(trifluoromethoxy)-phenylhydrazone (FCCP) led to 70%–90% reduction of the accumulation ratio. Though not as pronounced, diminished uptake was also observed in the presence of 140 μM nigericin, 161 μM valinomycin and 90 mM KSCN, commensurate with their effects on pmf. Accumulation of CH2O as a function of external pH followed a trend more similar to that of pmf than either δpH or δΨ. Preventing energization by incubation with 100 μM N,N′-dicyclohexylcarbodiimide (DCCD) led to nearly 80% inhibition of CH2O transport. Over short time periods it was possible to “chase” accumulated 14CH2O from previously loaded cells by collapsing pmf; however, this technique also indicated that significant 14CH2O incorporation began to occur within 3 min.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 506 (1987), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Bioprocess and biosystems engineering 4 (1989), S. 1-10 
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The availability and demand of biosynthetic energy (ATP) is an important factor in the regulation of solvent production in steady state continuous cultures of Clostridium acetobutylicum. The effect of biomass recycle at a variety of dilution rates and recycle ratios under both glucose and non-glucose limited conditions on product yields and selectivities has been investigated. Under conditions of non-glucose limitation, when the ATP supply is not growth-limiting, a lower growth rate imposed by biomass recycle leads to a reduced demand for ATP and substantially higher acetone and butanol yields. When the culture is glucose limited, however, biomass recycle results in lower solvent yields and higher acid yields.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Bioprocess and biosystems engineering 4 (1989), S. 81-89 
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Bead-bead collisions have been characterized using the velocity of the smallest turbulent eddies to calculate a turbulent collision severity (defined as the energy of collisions times their frequency), but a shear-based collision mechanism with a different dependence on the system variables is also applicable. This shearbased mechanism and the ratio of smallest eddy size to microcarrier diameter can explain the beneficial effects of both smaller diameter microcarriers and higher viscosity of the medium on the growth rate of bovine embryonic kidney cells. Death rates of these cells have also been measured at several levels of agitation. The decrease in apparent growth rate from increasing agitation is caused both by a higher rate of cell death as well as a lower intrinsic growth rate.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Bioprocess and biosystems engineering 4 (1989), S. 49-55 
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Using experimental data from continuous cultures of Clostridium acetobutylicum with and without biomass recycle, relationships between product formation, growth and energetic parameters were explored, developed and tested. For glucose-limited cultures the maintenance models for, the Y ATP and biomass yield on glucose, $$(Y_{X/G} ),1/Y_{{\text{ATP}}} = 1/Y_{{\text{ATP}}}^{\max } + m_e /\mu $$ and $$1/Y_{X/G} = 1/Y_{X/G}^{\max } + m_G /\mu $$ were found valid, as well as the following relationships between the butanol (Y B/G) or butyrate (Y BE/G) yields and the ATP ratio (R ATP, an energetic parameter), Y B/G =0.82-1.35 R ATP, Y BE/G =0.54 + 1.90 R ATP. For non-glucose-limited cultures the following correlations were developed, Y B/G =0.57-1.07 μ, Y B/G =0.82-1.35 R ATPATP and similar equations for the ethanol yield. All these expressions are valid with and without biomass recycle, and independently of glucose feed or residual concentrations, biomass and product concentrations. The practical significance of these expressions is also discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Biotechnology letters 5 (1983), S. 579-584 
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary It has been found that Methylomonas L3, an obligate methylotroph, has active transport systems for methanol and formaldehyde, and uses βpH as driving force for the formaldehyde system. The effects of substrate active transport on the dynamics of continuous cultures were demonstrated experimentally. These include unrealistic transient biomass yields. The dynamic studies also indicate that these active transport systems may be subject to genetic repression-induction controls.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Addition of 8–12 mM acetoacetate (AA) in uncontrolled-pH batch cultures ofC. acetobutylicum led to significant solvent production and averted the complete growth inhibition observed in control cultures. In controlled-pH cultures, the AA effect on solvent formation was not quite as pronounced, and that and the effect of 20 mM butyrate could be simulated and enhanced by the addition of FCCP, a potent uncoupler. The AA and butyrate effects on solvent production appear directly associated with their uncoupling action.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Biotechnology letters 7 (1985), S. 37-42 
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Carbon monoxide sparged in batch fermentations ofC. acetobutylicum inhibits the production of H2 by the hydrogenase and enhances the production of solvents by making available larger amounts of NAD(P)H2 to the cells. CO also inhibits biomass growth and acid formation. Its effect is most pronounced under fermentation conditions of excess carbon- and nitrogen-source supply.
    Type of Medium: Electronic Resource
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