Cell stationary 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. 

In the stationary phase, assuming that the total cell mass in the reactor is constant and that only L-phenylalanine and acetate are produced, the following stoichiometric equations are used ... 

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... 

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. 

Timm Steinbuchel (1990) revealed the production of PHAs by Pseudomonas aeruginosa. It was found that when the cell reached to stationary phase, the intracellular PHAs were decreased. Lageveen et al (1998) produced PHAs from n-octane by Pseudomonas oleovorans. 

In this example, one solute is used on the column. The / b(BSi) and J(BSi) values control the afiinity of the Si solute for the stationary phase. The parameters are shown in the Parameter Setup 6.4. In the report, the position of each solute cell is recorded in groups of five rows from 0 to 100 after a certain... 

Stationary phase, B, 300 cells (black) are distributed so that no two cells are closer than 3 cells... 

In phase B it is assumed that the inoculum has adapted itself to the new environment and growth then proceeds, each cell dividing into two. Cell division by binary fission may take place every 15-20 minutes and the increase in numbers is exponential or logarithmic, hence the name log phase. Phase C, the stationary phase, is thought to occur as a result of the exhaustion of essential nutrients and possibly the accumulation... 

With endogeneous pectic polysaccharides as substrates, the pectin methyhransferase activity was measured as radioactivity linked to oxalate-soluble polys x harides after extensive washing of microsomes with IM ethanolic NaCL Figure 2 shows that the rate of methylesterification of pectic substances was maximal on days 4 and 6 these maximum activities were observed within this period in at least five independent ejqjeriments. On the other hand, little activity was noted in young cells before day 2, and in old cells after day 9. In other words during the stationary phase the newly synthesised pectins remained unesterified because of the lack of pectin methyltransferase activity. 

The distribution of PG (PG) as culture medium supernatant, cell-wall associated and cell-bound enzyme was observed in K. marxianus during the time course of growth in 5% glucose medium (Table 2). PG secretion started between 8 and 12 h after inoculation and approximately 90% of total PG was secreted in early stationary phase. PG was not detected intracellularly after 24 h of growth. 

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. 

Colland, F., Fujita, N., Ishihama, A., and Kolb, A. (2002) The interaction between sigmaS, the stationary phase sigma factor, and the core enzyme of Escherichia coli RNA polymerase. Genes Cells 7, 233-247. 

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