Culture lag

Ogburn s theory of culture lag remained an important concept in postwar social scientific theory and was reworked in discourses of modernization, the scientific revolution, and automation. Until the 1950s modernization theorists had primarily seen the problem of acceleration as one of pre-modern cultures, but the rhetorical gap between the first and third worlds closed after Sputnik. In domestic science policy, rapid... 

Substantial progress has been made in developing defined, xeno-free media for human pluripotent stem cell culture. However, implementation of defined extracellular matrices for iPSC and hESC culture lags media development. While lab-scale culture is now relatively straightforward, there are substantial challenges in larger-scale culture for generating industrial- or clinical-quality pluripotent stem cells... 

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 ... 

Batch fermentation is the most widely used method of amino add production. Here the fermentation is a dosed culture system which contains an initial, limited amount of nutrient. After the seed inoculum has been introduced the cells start to grow at the expense of the nutrients that are available. A short adaptation time is usually necessary (lag phase) before cells enter the logarithmic growth phase (exponential phase). Nutrients soon become limited and they enter the stationary phase in which growth has (almost) ceased. In amino add fermentations, production of the amino add normally starts in the early logarithmic phase and continues through the stationary phase. 

The logistic equation leads to a lag phase, an exponential initial growth rate and a stationary population of concentration (xm). In a population, it is often the case that the birth rate decreases as the population itself increases. The reasons may vary from increased scientific or cultural sophistication to a limited food supply. 

Figure 3.7 shows the growth of R. rubrum in a batch fermentation process using a gaseous carbon source (CO). The data shown follow the logistic model as fitted by (3.14.2.11) with the solid lines, which also represent an unstructured rate model without any lag phase. The software Sigma Plot was used to fit model (3.14.2.11) to the experimental data. An increase in concentration of acetate in the prepared culture media did not improve the cell dry weight at values of 2.5 and 3 gT-1 acetate, as shown in Figure 3.7. However, the exponential growth rates were clearly observed with acetate concentrations of 0.5-2 g-F1 hi the culture media.

Models for batch culture can be constructed by assuming mechanisms for each phase of the cycle. These mechanisms must be reasonably comph-cated to account for a lag phase and for a prolonged stationary phase. Unstructured models treat the cells as a chemical entity that reacts with its environment. Structured models include some representation of the internal cell chemistry. Metabolic models focus on the energy-producing mechanisms within the cells. 

The first phase, A, is called the lag phase. It will be short if the culture medium is adequate, i.e. not necessarily minimal, and is at the optimum temperature for growth. It may be longer if the medium is minimal or has to warm up to the optimum growth temperature, and prolonged if toxic substances are present other things being equal, there is a relationship between the duration of the lag phase and the amount of the toxic inhibitor. 

The lag after diluting glucose-grown cultures of Escherichia coli into fresh medium may be eliminated by the addition of NaHCOj and is consistent with the requirement of this organism for low concentrations of COj for growth (Neidhardt et al. 1974). 

Lankford CE, Walker JR, Reeves JB, Nabbut NH, Byers BR, Jones RJ (1966) Inoculum-Dependent Division Lag of Bacillus Cultures and its Relation to an Endogenous Factor(s) ("Schizokinen"). J Bacteriol 91 1070... 

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