Cell growth rates

There several DO probes available. Some well-known branded fermenters, like New Brunswick, Bioflo series and the B. Braun Biotstat B fermenters are equipped with a DO meter. This unit has a 2 litre fermentation vessel equipped with DO meter and pH probe, antifoam sensor and level controllers for harvesting culture. The concentration of DO in the media is a function of temperature. The higher operating temperature would decrease the level of DO. A micro-sparger is used to provide sufficient small air bubbles. The air bubbles are stabilized in the media and the liquid phase is saturated with air. The availability of oxygen is major parameter to be considered in effective microbial cell growth rate. 

Table 3.1 shows the kinetic parameters for cell growth, rate models with or without inhibition and mass transfer coefficient calculation at various acetate concentrations in the culture media. The Monod constant value, KM, in the liquid phase depends on some parameters such as temperature, initial concentration of the carbon source, presence of trace metals, vitamin B solution, light intensity and agitation speeds. The initial acetate concentrations in the liquid phase reflected the value of the Monod constants, Kp and Kp. The average value for maximum specific growth rate (/xm) was 0.01 h. The value... 

Once there is an appreciable amount of cells and they are growing very rapidly, the cell number exponentially increases. The optical cell density of a culture can then be easily detected that phase is known as the exponential growth phase. The rate of cell synthesis sharply increases the linear increase is shown in the semi-log graph with a constant slope representing a constant rate of cell population. At this stage carbon sources are utilised and products are formed. Finally, rapid utilisation of substrate and accumulation of products may lead to stationary phase where the cell density remains constant. In this phase, cell may start to die as the cell growth rate balances the death rate. It is well known that the biocatalytic activities of the cell may gradually decrease as they age, and finally autolysis may take place. The dead cells and cell metabolites in the fermentation broth may create... 

In addition to desulfurization activity, several other parameters are important in selecting the right biocatalyst for a commercial BDS application. These include solvent tolerance, substrate specificity, complete conversion to a desulfurized product (as opposed to initial consumption/removal of a sulfur substrate), catalyst stability, biosurfactant production, cell growth rate (for biocatalyst production), impact of final desulfurized oil product on separation, biocatalyst separation from oil phase (for recycle), and finally, ability to regenerate the biocatalyst. Very few studies have addressed these issues and their impact on a process in detail [155,160], even though these seem to be very important from a commercialization point of view. While parameters such as activity in solvent or oil phase and substrate specificity have been studied for biocatalysts, these have not been used as screening criteria for identifying better biocatalysts. 

We have studied CNT influence on growth rate and proliferation of some cellular colonies [29]. Interesting results were obtained in case of bread-making yeast-like fungi Saccharomyces cerevisiae (strain 608) and hamster kidney cells. Introduction of small amounts of CNT ( 3 pg/mL) in fungal suspensions led to 2-fold increase in Saccharomyces cerevisiae colonies number compared to the control, after 48 h of incubation at 30°C (Fig. 2.2). Similar results were obtained for colonies of hamster kidney cells. Presence of CNT activated cell proliferation and increased cell growth rate by 1.5 times. 

High Cell Density Culture The fed-batch operation that maintains the substrate concentration at a suitable value for a high cell-growth rate can achieve a high cell concentration (50-100gl ). 

Suppose that a well-mixed stirred tank is being used as a fed-batch fermentor at a constant feed rate F (m h ), substrate concentration in the feed C j (kg m ), and at a dilution rate D equal to the specific cell growth rate p. Ihe cell concentration Cjj (kgrn ) and the substrate concentration (kgm ) in the fermentor do not... 

Various natural and xenobiotic compounds have been studied for their ability to be the sole support of growth for microorganisms (Table 17.6). Sometimes enrichments simply isolate a pre-existing subpopulation of bacteria from the mixture of organisms present in a natural sample however, other times a mutation must occur which permits survival on the chemical provided (e.g., Brunner et al., 1980). From the data shown in Table 17.6, a few cautious generalizations can be made. First, maximum cell growth rates for acclimated cultures appear to correspond to doubling times of hours (recall... 

Smeda et al. (1993) reported that in a mutation of the psb A gene in a photoautotropic potato, atrazine resistance was attributable to a mutation from AGT (ser) to ACT (threonine) in codon 264 of the psb A gene that encodes the Qb protein. Although the mutant cells exhibited extreme levels of resistance to atrazine, no concomitant reductions in photosynthetic electron transport or cell growth rates were detected compared to the unselected cells. This is in contrast with the losses in productivity observed in atrazine-resistant mutants that contain a Ser to Gly 264 alteration. Research has shown that triazine resistance by various algae and photosynthetic bacteria has been due to changes in many different binding sites (Oettmeier, 1999). 

Here /rmax is the nomenclature for the maximum cell growth rate [typically in h-1 (reciprocal hours)] and Cx is the mass concentration of cells (g/L). Hence the cell growth rate initially is exponential with time (called the exponential growth phase). 

Unfortunately, the cell growth rate is limited or inhibited by a number of factors. First is the limitation created by the substrate S or some other nutrient. The Monad kinetic model is typically used to represent the behavior of such biochemical systems according to the following equation ... 

Here ji is the specific cell growth rate (h-1), Cs is the substrate concentration, and Ks is a constant that is equal to the value of substrate concentration at half the maximum cell growth rate. This model produces the relationship shown in Figure 1.5. At low substrate concentrations, the growth rate is first-order with respect to Cs- At high substrate concentrations, the specific growth rate is independent of concentration. The value of Ks determines how quickly we reach the maximum specific growth rate. 

In addition to the depletion of substrate (or a lack of oxygen in aerobic systems), the cell growth rate can also be slowed by inhibition caused by products generated by the cells themselves (the desired product or byproducts such as carbon dioxide). This is incorporated into the kinetic rate expression by the effect of an inhibition term ... 

Figure 1.5 Normalized cell growth rate as a function of substrate concentration.

Here Cp is the product concentration, Cp>max is the maximum product concentration when cell growth stops, and nP is the order of inhibition. At low values of Cp, the inhibition term plays no significant role. However, as the product concentration increases, the cell growth rate begins to decrease until the biomass concentration eventually reaches a plateau (what is called the stationary phase). From there, the fermentation broth is typically harvested before the cells start to die and the biomass concentration starts to decrease. 

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