Cell mass concentration

Off-line determination of biomass concentration by classical gravimetric methods requires cell separation, washing steps and drying to constant weight. The separation of cells can be made either by centrifugation or by filtration. 

In contrast, the filtration method is more expensive (filters cannot be reused) but works with smaller net weights (i.e. sample volumes) and is usually more rapid, provided the cells are not slimy and do not clog the filter. Nylon or PVDF filters withstand the pre-drying procedure excellently whereas modified cellulose filters lose their mechanical robustness. 

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When the cell concentration is appreciable, the dilution rate must reach a specific rate (X / 0, D = ft). The cell mass concentration is defined in (6.8.1.13) as the dilution rate approaches zero the cell density is the product of yield and initial substrate concentration ... 

P/Xt Productivity, relation of product P to cell mass concentration X and time t q Gas throughput... 

T. Suizuki, H. Mori, T. Yamane, S. Shimizu (1985) Automatic supplementation of minerals in fed-batch culture to high cell mass concentration Biotechnol. Bioeng., 27 192-201. 

The representation of the biological conservation of substrate to cell mass by an overall chemical reaction. The stoichiometric relationships are then used to calculate various rates such as cell mass concentration [83]. 

The BioView sensor includes a software package (CAMO ASA, Norway) for data analysis and on-Une estimation of different bioprocess variables simultaneously. Thus, the instrument is able to predict the trends of the concentration courses of different variables during a cultivation and is used to give information about important process steps (e.g., feeding time, harvesting time, etc.). The instrument is able to monitor on-line several fluorophores in situ and non-invasively during cultivation processes and permits an estimation of different bioprocess variables simultaneously. The increasing of cell mass concentration and the product formation as well as the actual metabolic state of the cells is simultaneously detectable by this fluorescence technique. 

The cell concentration is usually expressed by the cell number density C (the number of cells per unit volume of medium), or by the cell mass concentration... 

Yeast cells grow in the exponential phase. The cell mass concentrations are given in Table 4.4. Calculate the specific growth rate,... 

If the respiration rate of the cells under the present condition is 0.08 g-O2 (g dry cell)h", estimate the cell mass concentration (g dry cell m" ). 

Cultivation Cell mass Concentration (g/L) Monomer yield... 

Prior to the fermentations, the pH of the different hydrolysate samples was adjusted to 5.5 with NaOH (5 M). All fermentations were carried out under oxygen-limited conditions in 55-mL glass vessels containing 50 mL of medium of which 47.5 mL was hydrolysate (or, alternatively, an aqueous glucose solution for reference fermentations). The vessels were sealed with rubber stoppers and equipped with cannulas for outlet of C02. The hydrolysates were supplemented with nutrients as previously described (20). Fermentations of 35 g/L of glucose and nutrients but no hydrolysate were used for reference. The flasks were inoculated to an initial cell mass concentration of 2.0 g/L dry wt and incubated at 30°C with stirring. The fermentations were run for 36 h. Samples of 200 pL were taken after 0,2,4, 6, 8,10, 24, and 36 h. 

Specific growth rate coefficient, l The rate of change of microbial cell mass concentration per unit cell concentration p = (l/Cx)(dCx/dt) (where Cx = cell mass concentration, g/1). 

As can be seen from Table 8.7 productivity (expressed in g h b is highest for precursor addition. The production of L-phenylalanine from phenylpyruvic add also has the shortest reaction time to obtain hi conversions. The pH commonly used is around 75, quite normal for biological processes. Only the enzyme phenylalanine ammonia lyase shows an optimiim pH of lO.The process temperature varies between 30 and 40°C with an average of 35°C. No extreme temperatures have been reported due to the fact that denaturation occurs at hi temperatures. The optimal concentration for cells frequently used is 10-20 g 1". However, conversion of ACA is done with hi cell mass concentrations in recent studies possibly to compensate for substrate inhibition and thus to maintain hi product concentration. The processes using PPA and ACA need an amino add as amino donor, usually L-aspartic add is used. 

In many biotechnology applications, such as fermentation broth clarifications to produce common antibiotics, optimal values of TMP are in the range of 2 to 3 bar (15 to 30 psi) especially at high cell mass concentrations (> 30 wt.%) and cross-flow velocity range of 4 to 7 In the operation... 

The on-line direct measurement of cell mass concentration by using optical density principles promises to dramatically improve the knowledge of the metabolic processes underway within a bioreactor. This measurement is most effective on spherical cells such as E. Coli. The measurement technology is packaged in a sterilizable stainless steel probe which is inserted directly into the bioreactor itself via a flange or quick-discoimect mounting (Fig. 1). 

The cell concentration is usually expressed by the cell number density Cn (the number of cells per cubic meter of medium), or by the cell mass concentration Cx (the dry weight, in kg, of cells per cubic meter of medium). For any given size and composition of a cell, the cell mass and the cell number per unit volume of medium should be proportional. Such is the case of balanced growth, which is generally attained under some suitable conditions. The growth rate of cells on a dry mass basis, rx (expressed as kg dry cells m-3h-1), is defined by ... 

Regarding the value of — logT vs. cell mass concentration, X a linear relationship was established. Values of 2T = 0.255 mg dry cell/ml which correspond to —l(>gT=0.5 could be converted via the counting with a hemacytometer to the cell number concentration, N = 4.1 x 10 cells/ml. 

MV mean value SD standard deviation Gr.A group A [pm-e silicone oil and poly(propylene glycol) PPG and silicone oil/PPG mixture] Gr.B group B (aqueous emulsion with only 10% S184) X cell mass concentration Yx/s yield coefficient of growth with respect to substrate P productivity of P-galactosidase SP specific productivity SG specific glucose consumption rate [51]... 

In synthetic medium and with a mean residence time of 6.5 h (dilution rate D = 0.15h ) and 10 gl glucose only 1.9 gl cell mass concentration was obtained. The flotation of this medium yielded a cell-free residue (Cr = 0.0 g 1 ) and high cell mass concentration in the foam C = 81 g 1". The separation factor S was infinite. When the same medium was supplemented wiA a mixture of inositol, pantothenate and pyridoxine, 4.8 gl" cell mass concentration was obtained. By flotation of this medium with a 3 ml s aeration rate C = 65 gl, Cr = 80 mg 1 and S = 812 were obtained. 

In the following, we will use the (dry) cell mass concentration, X, to describe cell growth. 

In perfectly mixed batch reactors the cell mass concentration is constant everywhere, hence eqs. (1) and (3) can be used. 

Fig.2.Dimensionless cell mass concentration at reactor outlet 5 1)-X/Xo as a function of Da for different Bo-numbers.Steady state operation. Nonsterile feed (X > 0) (1). ...

The requirement of positive cell mass concentration is fulfilled only, if... 

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