Batch culture growth

In fed batch culture, growth rate is controlled by the rate of feeding of the limiting nutrient. The feed rate can therefore be used to set qp and the desired productivity of protein production. 

Figure 2.6. Logarithmic plot of a typical batch culture growth curve.

Figure 2.7. Arithmetic plot of a typical batch culture growth curve (same data as used to construct Figure 2.6).

Fed-batch culture A cell cultivation technique in which one or more nutrients are supplied to the bioreactor in a given sequence during the growth or bioconversion process while the products remain in the vessel until the end of the run. 

As you might have already gathered, the majority of industrial fermentations are batch processes. In closed batch systems, the growth medium is inoculated with cells and growth and product formation is allowed to proceed until the required amount of conversion has taken place. After harvesting the culture the vessel is cleaned, sterilised and filled with fresh medium prior to inoculation. For some processes, addition of all the feedstock prior to inoculation, as is done in closed batch fermentations, is undesirable and it is preferable to incrementally add the carbon source as the fermentation proceeds. Such a process is known as fed-batch culture and the approach is often used to extend the lifetime of batch cultures and thus product yields fed-batch cultures are considered further in Section 2.7.4. 

When excess substrate interferes with growth and/or product formation. One example is the production of baker s yeast. It is known that relatively low concentrations of certain sugars repress respiration and this will make the yeast cells switch to fermentative metabolism, even under aerobic conditions. This, of course, has a negative effect on biomass yield. When maximum biomass production is aimed at, fed batch cultures are the best choice, since the concentration of limiting sugar remains low enough to avoid repression of respiration. 

These comments also apply to batch cultures where product formation occurs after growth has ceased. 

False. Continuous cultures operate for lengthy periods. Spontaneous mutations will arise and if they can compete successfully with the parent organism (by virtue of higher growth rate) they can predominate in the culture. Batch cultures have short growth times and so do not suffer such drawbacks. 

False. Batch cultures can convert high proportions of substrates, as growth can be allowed to proceed until substrates are exhausted. In continuous cultures substrates are never fully converted, as medium is continuously removed. In fact, residual substrate concentration increases as the dilution rate increases, until virtually all of the medium remains unused. Continuous cultures usually recycle the medium after biomass removal to increase the efficiency of substrate conversion. 

Batch. Batch cultures have a stationary phase during which little or no growth occurs. 

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 rate of product formation, rfi, depends upon the state of the cell population, environmental condition, temperature, pH, media composition and morphology with cell age distribution of the microorganism.2 3 A similar balance can be formulated for microbial biomass and cell concentration. The exponential phase of the microbial growth in a batch culture is defined by ... 

Exponential growth in a batch culture may be prolonged by addition of fresh medium to the fermentation vessel. In a continuous culture the fresh medium has to be displaced by an equal volume of old culture, then continuous cell production can be achieved. 

The effect of substrate concentration on specific growth rate (/i) in a batch culture is related to the time and p,max the relation is known as the Monod rate equation. The cell density (pcell) increases linearly in the exponential phase. When substrate (S) is depleted, the specific growth rate (/a) decreases. The Monod equation is described in the following equation ... 

Mars AE, J Houwing, J Dfolfing, DB Janssen (1996) Degradation of toluene and trichloroethylene by Burk-holderia cepacia G4 in growth-limited fed-batch culture. Appl Environ Microbiol 62 886-891. 

The procedure for the estimation of qs and qp is identical to the one presented for fed-batch and continuous cultures. The only difference is in the estimation of the specific growth rate (p). Since perfusion cultures behave as batch cultures as far as the biomass is concerned, p can be obtained as described earlier for batch systems. Namely p is obtained as the slope in the plot of / Xv(t,) versus t,. 

Andersen et al. (1996) and Andersen (1995) have studied the effect of temperature on the recombinant protein production using a baulovinis/insect cell expression system. In Tables 17.15, 17.16, 17.17, 17.18 and 17.19 we reproduce the growth data obtained in spinner flasks (batch cultures) using Bombyx mori (Bm5) cells adapted to serum-free media (Ex-Cell 400). The working volume was 125 ml and samples were taken twice daily. The cultures were carried out at six different incubation temperatures (22, 26,28, 30 and 32 TT). 

Table 17.15 Growth of Bm5 Cells Growth Data taken from a Batch Culture of Bm5 Cells Incubated at 22 TT...

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