Exponential phase

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 maximum yield, as can be seen from Figure 85, is in the late exponential phase. Using the data given in Table 8.4 for the interval between 14 and 24 hours, we obtain a value of 0.27 g phenylalanine (g glucose) 1 for the maximum yield coefficient... 

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 ... 

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 ... 

A limiting case of Monod kinetics has Ks = 0 so that cell growth is zero order with respect to substrate concentration. Rework Example 12.7 for this situation, but do remember to stop cell growth when S = 0. Compare your results for X and p with those of Example 12.7. Make the comparison at the end of the exponential phase. 

Sub-cellular fractionation of five strains reveal the same numbers of bands. The distribution of PG activity in sub-cellular organelles was broadly similar in these five strains. PG activity was detected in low-density vesicles, vacuoles and ER fractions in samples harvested during the early exponential phase of growth. However, PG levels were always lower (at least 1.5 fold) than those found in wild type. Cells of the mutants harvested during stationary phase of growth showed that 84% of total intracellular PG activity was located in the vesicle fraction. No intracellular PG activity was found in stationary phase wild type cells. 

Cuthbertson KS, Whittingham DG, Cobbold PH 1981 Free Ca2+ increases in exponential phases during mouse oocyte activation. Nature 294 754—757 Day ML, Johnson MH, Cook DI 1998 A cytoplasmic cell cycle controls the activity of a K+ channel in pre-implantation mouse embryos. EMBO J 17 1952—1960 Flach G, Johnson MH, Braude PR, Taylor RA, Bolton VN 1982 The transition from maternal to embryonic control in the 2-cell mouse embryo. EMBO J 1 681-686 Howlett SK 1986 A set of proteins showing cell cycle-dependent modification in the early mouse embryo. Cell 45 387-396... 

Real-time PCR is a quantitative method for measuring amplicons as they are produced by measuring the increase in fluorescence of a dye added to the reaction mixture.12,104,105 Methods using fluorescent reporters, such as SYBR Green,104,106 TaqMan ,107,108 or molecular beacons,9 collect quantitative data at the time when DNA is in the exponential phase of amplification. 

Algal cultures in exponential phase are used for inoculating Petri dishes containing agarized culture medium... 

However, precise fits require the use of at least second order models, which include three characteristic phases in the biodegradation process [4] (i) an acclimatisation or lag phase (ii) an exponential phase with most of the effective degradation and (iii) a final phase in which the microorganism population is stable and some portion of the substrate could persist (see Fig. 5.3.1(a) [21]). 

HCT-116 human colon carcinoma (ATCC, Bethesda MD) cells were grown in McCoy s 5A) and were routinely subcultured twice weekly. Antiproliferative assay was performed by chemoluminescence assay based on quantification of ATP. Cells in their exponential phase of growth were treated at different times (lh or 24h) with different concentrations of edotecarin or SN-38. For post-treatment recovery studies, cells were washed with PBS and left in drug-free culture medium. Then, cell medium was collected to avoid any cell loss. Cells in monolayer were washed, detached with trypsin, and collected in the medium. Cells were counted in a Multisizer 3 Coulter Counter to measure the drug s effects on growth inhibition. Samples were fixed either... 

E. coli DH5a (pJF119fsa) strain was conserved at —80°C in glycerol stocks prepared from exponential-phase cultures. 

Five different concentrations (0, 25, 50, 75, 100 mg/1) of explosives were added to the cultivation medium from stock solution of TNT (100 mg/ml, DMSO). The experiment were done in triplicates for particular concentration and harvest-day. The concentration which inhibits growth of suspension culture by 50% (IC50), was calculated from GVs, which corresponded to the end of exponential phase of growth and which differed for particular species. The GVs for different concentration of explosives were plotted and IC50 calculated. 

Figure 5.17 Growth of a propene utilising Mycobacterium sp in batch culture exhibiting typical growth kinetics 1) lag phase 2) acceleration 3) exponential phase 4) deceleration 5) stationary phase 6) decline.

Inhibition of Exponential Phase Cultures of Clostridium sporogenes by Nitrate, Nitrite, and Nitric Oxide"... 

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