Cell 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 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... 

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... 

Yeast cells grow in the exponential phase. The cell mass concentrations are given in Table 4.4. Calculate the specific growth rate,... 

In another set of experiments, Schlesinger and Anderson (44) showed that the isozymes are formed in vivo by alteration of the dimer. Using an E. coli mutant that makes an altered subunit, which will only dimerize (in vitro or in vivo) in the presence of phosphate or zinc, they found that the monomers produced by the cell growing in the absence of phosphate and zinc produced only one electrophoretic form when the monomer was converted to the dimer in vitro. However, if the medium is made 2 vaM in phosphate and 10 /iM in zinc, in the exponential phase of growth, three isozymes are formed. Additional support for the conclusion that isozymes are made by alteration of the dimer comes from the fact that independent of when 14C-labeled amino acids are added to the growing culture, label appears first in isozyme I. It thus appears that a mechanism is available in the periplasmic space for the conversion of isozyme I to the other isozymes. 

The growth of microbial populations is normally limited either by the exhaustion of available nutrients or by the accumulation of toxic products of metabolism. As a consequence, the rate of growth declines and growth eventually stops. At this point a culture is said to be in the stationary phase. The transition between the exponential phase and the stationary phase involves a period of unbalanced growth during which the various cellular components are synthesized at unequal rates. Consequently, cells in the stationary phase have a chemical composition different from that of cells in the exponential phase. 

The inoculum was prepared from the stock culture in 500-mL Erlen-meyer flasks containing 100 mL of the corresponding medium. Incubation was performed in a rotary shaker at 200 rpm and 30 1°C for 48 h with the cells in the exponential phase of growth. 

Inocula were prepared by adding a loopful of cells from the stock culture to 100 mL of Difco nutrient broth and incubating at 30°C for 16 h on a rotatory shaker at 150 rpm. Inoculation volumes corresponding to about 0.04 g/L of exponential-phase cells were used. 

The maximum biosurfactant production was verified at pH 7.0 and 8.0. The addition of EDTA and microsalts favored microbial synthesis of surface-active compounds. On the other hand, the addition of yeast extract stimulated cell growth to the detriment of biosurfactant production. The most suitable concentration of commercial sucrose for biosurfactant synthesis was 10 g/L. Biosurfactant production occurred in the late-exponential phase, achieving its maximum value at the early stationary phase of growth. The values of surface tension that we obtained compare favorably with those obtained with commercial synthetic surfactants. 

Cell growth phases comprise lag phase, exponential or log growth phase, stationary or plateau phase, and senescence or death phase, as shown in Figure 2.5. Cell growth can be mathematically represented by the following general equation ... 

Normal animal cell growth curve pattern, in which p is the specific cell growth rate. Lag phase (A) represents the culture adaptation period, followed by an exponential cell growth phase (B) until the attainment of a stationary or plateau phase (C), in which there is no increase in cell number. The culture reaches the senescence phase (D) when the percentage of cells in division becomes lower than the percentage of cells dying. 

Complete medium, cells harvested in mid-exponential phase... 

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