Cell Growth Measurement

To follow the course of growth, it is necessary to make quantitative measurements. Cell growth can be determined by measuring cell number, cell mass, or cell activity. 

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When microbial cells are incubated into a batch culture containing fresh culture media, their increase in concentration can be monitored. It is common to use the cell dry weight as a measurement of cell concentration. The simplest relationships describing exponential cell growth are unstructured models. Unstructured models view the cell as an entity in solution, which interacts with the environment. One of the simplest models is that of Malthus 19... 

The effect of a particular cultivation environment on a system can be evaluated in terms of biomass (fresh/dry weight, cell number), secondary metabolite production [51,75,89,102,103,106,107] or substrate consumption (e.g. carbon source [57] or oxygen [53,108]). Using the Evan s Blue method to identify non-viable cells. Ho et al. [108] used viable cell density measurements to determine variations in specific growth rate attributable to hydrodynamic stress. 

Figure L pH, nitrite, nitrate, and NDMA concentration as a function of cell growth in VL medium, E. coli ATCC 11775 was inoculated into sealed tubes containing VL medium (described in the legend to Table 1) supplemented with 0,2% glucose, 0.05% dimethylamine, and 0,08% sodium nitrate. The tubes were incubated at 37°C and cell growth was followed with spectronic 20 (Bausch Lomb) at 660 nm. Nitrite and nitrate were measured as described in ( ) and NDMA detection as described in the legend to Table I,...

A very versatile piece of equipment that is affordable for individual laboratories is the microplate reader. This allows multiple samples to be analyzed at once, commonly in a 96-well format, although 384- and 1536-well formats are available. Typical measurements that can be performed include UV-Vis absorbance, fluorescence, or luminescence, allowing a range of assays to be performed, such as cell growth, enzyme kinetics, enzyme stability, or enzyme-linked immunosorbent assay [60-62]. Functionality can be increased by the use of liquid dispensing systems or automatic plate handling. 

Bioassays of related substances can be quite similar in design. Specific growth factors, for example, stimulate the accelerated growth of specific animal cell lines. Relevant bioassays can be undertaken by incubation of the growth-factor-containing sample with a culture of the relevant sensitive cells and radiolabelled nucleotide precursors. After an appropriate time period, the level of radioactivity incorporated into the DNA of the cells is measured. This is a measure of the bioactivity of the growth factor. 

For more than 80 years, tree-ring data have been used to make inferences about past climatic variation. In general, the characteristic most often used has been the variations in widths of the annual growth rings. However, during the past decade other properties, such as cell density (measured by x-ray densiometric techniques), relative widths of early and late wood, and isotopic composition of the cellulose have been used to infer past environmental conditions. It is the isotopic composition that is of interest here. 

Our laboratory uses a mouse model to study preventative and therapeutic vaccination strategies for human papilloma virus (HPV)-associated tumors. For preventative vaccination studies, six- to eight-week-old female C57BL/6 mice are injected subcutaneously with LPDI on days 0 and 5 and are challenged on day 10 with a subcutaneous injection of 10 E7-expressing TC-1 tumor cells with tumor growth measured three times weekly. 

Unnatural amino acids are added to the growth medium in most experiments. There are a large number of amino acid and amine transporters that are relatively nonspecific and which may help to transport the unnatural amino acids into cells. From measurements of cytoplasmic levels of amino acids, it is found that a large number of unnatural amino acids are efficiently transported to the E. coli cytoplasm in millimolar concentrations. Highly charged or hydrophilic amino acids may require derivatization (e.g., esterification, acylation) with groups that are hydrolyzed in the cytoplasm. Metabolically labile amino acids or analogues (e.g., a-hydroxy acids, A-methyl amino acids) may require strains in which specific metabolic enzymes are deleted. 

It has been shown that radio frequency impedance (RFI) is an effective tool for moifitoring cell density and cell growth of bioprocesses. The fermentation process, quite complex, is oftentimes difficult to sample and monitor. The RFI measurement could detect cell viability of Escherichia coli during the fermentation, serving as a qualitative measure of the metabolic load of the cell, and thus provide an in situ indicator of the optimal harvesting times. 

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