Measurement of Cell Mass

A calibration curve can be obtained by measuring the absorbance of the samples with known cell concentration. The measurements are usually made at a wavelength of 600 700 nm. 

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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). 

K. Suehara, Y. Nakano, T. Yano. Application of near infrared spectroscopy to the measurement of cell mass in solid cultures of mushroom. J Near Infrared Spectrosc 6 273-277,... 

One interesting paper by Suehara et al. used NIR to measure the cell mass in solid cultures of mushroom.41 Because mushrooms grow in solid matrices, spectroscopic analyses are sometimes difficult to perform. With coffee grounds as the main medium, reflection NIR was used for the determinations. The correlation between the glucosamine (analyte determined) predicted and that found by the conventional method was 0.992 with an SEP of 0.346 mg/g. 

Define the unit dalton. From this definition, compute the mass of 1 Da in grams. The mean of 60 measurements of the mass of individual E. coli cells vaporized by MALDI and measured with a quadrupole ion trap was 5.03 ( 0.14) X 10 °Da.3 Express this mass in femtograms. 

Cell Components For cultures undergoing balanced growth, the macro-molecular cell components such as protein, RNA, and DNA can be measured instead of cell mass. However, care is needed because the proportion of these materials in a cell can change with time if the culture does not undergo balanced growth. 

Cells can be represented by a single component, such as cell mass, cell number, or the concentration of protein, DNA, or RNA. This is true for balanced growth, since a doubling of cell mass for balanced growth is accompanied by a doubling of all other measurable properties of the cell population. 

Figure 5.10.3 Calculation of cell mass by on-line measurement of ATP, allowing a constant growth rate to be maintained. OD = optical density EDP = electronic data processing.

Koch and Schaechter (K3) have pointed out a number of unsatisfactory features in use of cell age as an index or measure of cell structure. In particular they note that the model based on this predicts no correlation between the life spans of sister cells, whereas in fact these life spans are found to be correlated. Again, they note that the mass of cells at division (bacterial cells, at any rate) shows less spread about a mean value than does the age of cells at division. They also report that they have found that the mean size of bacteria, at division, changes in a regular fashion when cells are transferred to a medium in which growth rate and bacterial size are different. 

Figure I. Experimental arrangement showing confining cell and sample with axial fracture. Flow at prescribed flow-rate and measured pressure drop records permeability. Constraint on process is provided by measurement of dissolved mass efflux, and periodic scanning by x-ray CT.[Polak et ai, 2003]...

The analysis of electrodiffusion measurements results, in terms of the mass transfer intensity, especially at high current densities, demonstrates that the design of bipolar plate with spots-like channels is preferable, regardless the possibility of existence dead zones in comers of bipolar plate. However, as the measurements of cell resistance caused first of all by contact area between bipolar plates demonstrate, the channel flow field structure generally leads to better performance of the fuel cell in comparison to spots- and meander-like structure. 

It must be clear from the various equations developed above that the gas-liquid interfacial area is a very important parameter in determining the rate of mass transfer. Any precise measurement of the mass transfer coefficient is possible only if the area is correctly known. This is best accomplished by using a stirred cell with a fixed gas-liquid interfacial area, although other experimental reactors such as the wetted wall column, laminar jet, and disk contactor can also be used (see Danckwerts, 1970 Doraiswamy and Sharma, 1984). The two commonly used cell designs are those of Danckwerts (1970) and Levenspiel and Godfrey (1974). 

Mass spectrometrists have always been concerned with the measurement of the mass and intensity of analyte ions. Investigation/utilization of the shapes of molecules is now possible with ion mobility techniques that utilize differences in the cross sections of ions as they move through a gas. Think in terms of two pieces of paper, one crumpled and the other flat. If dropped at the same time, the crumpled one will hit the floor first because it will encounter less air resistance than the flat piece. A similar situation applies to ions with different shapes as they travel through a gas. Although ion mobility has been examined with home-built instruments for years, only recently has this type of analyzer become available commercially. There are two significantly different types, the high-field asymmetric waveform ion mobility spectrometer (FAIMS) and the ion mobility separator (IMS). The FAIMS separator is placed between the ion source and the analyzer, while the IMS cell is located between the analyzers of an MS/MS instrument. 

Figure 2.22. Schematic representation of the basic experimental situation in bio-process/bioreactor analyses, where the interactions between physical transports (kj ) and biokinetic rates (kh) in the liquid phase are thought to be representative for the process rates in the solid phase of cell mass (kf,). At the same time, response lags of measuring electrodes (k ) have to be taken into account. G, gas phase L, liquid phase S, solid phase or substrate E, enzyme or electrode I, intermediary metabolites or products P, end product N, nucleus R, ribosomes M, mitochondria a, anabolism jS, catabolism Fq = gas flow rate n = agitators rotational speed.

The problem with rapid electrode reactions is that they become mass transport controlled at a rather low overpotential, masking any possibility for the determination of kinetic parameters. In such cases it is desirable to have methods which require only very small overpotential so that diffusion is still a minor factor in the kinetics. The measurement of cell impedance at the equilibrium potential gives, under certain conditions, such a possibility. 

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