Balancing changing cultures

Butanediol is produced during oxygen limited growth by a fermentative pathway known as mixed acid-butanediol pathway (Figure 4) (222). The 2,3-BD pathway and the relative proportions of acetoin and butanediol serve to maintain the intracellular NAD/NADH balance in changing culture conditions. The theoretical... 

This is an old, familiar analysis that applies to any continuous culture with a single growth-limiting nutrient that meets the assumptions of perfect mixing and constant volume. The fundamental mass balance equations are used with the Monod equation, which has no time dependency and should be apphed with caution to transient states where there may be a time lag as [L responds to changing S. At steady state, the rates of change become zero, and [L = D. Substituting ... 

The substrate balance in a batch culture for component i in the culture volume of VR and change of molar concentration of C, is equal to the rate of formation of product ... 

If the pH is adjusted as part of an engineered remediation, the microbial balance may be upset and bioreactions slowed until the microbe cultures adjust to the new conditions. Alternatively, if the release of organic chemicals has altered the pH outside the natural range, it may be necessary to add certain chemicals (i.e., aluminum sulfate, carbon dioxide, sodium hydroxide, etc.) to return the pH to preexisting conditions. Changes of pH should be monitored since rapid changes of more than 1 to 2 pH units over a short period can inhibit microbial activity and may extend the acclimation period before the microbes adapt and renew activity. 

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. 

Among the first cell viability assays developed for HTS was the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] tetrazolium reduction assay (Mosmann 1983) that served as a milestone for this type of study. The assay offered a non-radioactive alternative to tritiated thymidine incorporation into DNA as a method of measuring cell proliferation. In many cases, the MTT assay can directly substitute for the tritiated thymidine incorporation assay (Figure 6.3). The MTT tetrazolium compound is prepared in a physiologically balanced solution, added to cells in culture, and incubated for approximately 4 hr. Viable cells convert MTT into an intensely colored formazan product that can be quantitated by recording changes in absorbance at specific wavelengths. 

Africa is rich with variation of traditional cultures which have existed for centuries in equilibrium with their environment. Today, population growth in Africa, changing technologies, and altered life-styles have made the balancing mechanisms ineffective. Social-ecological systems which took centuries to evolve are being broken down with disastrous results for both humans and their life-supporting environment. 

While tissue culture is becoming more and more a science, it is still an art and, as such, the same rules of trial and error still apply the surface needed depends on the cell type. It is best to start with regular tissue culture-treated plasticware and then to proceed to the more complex biocoatings, realizing that this is a complex factor analogous to changing media and serum. All three systems - serum, media and coating - need to be balanced in that case. 

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