Logarithmic growth 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. 

An exponential (or logarithmic) growth phase follows the lag phase, and during this period the cell mass increases exponentially. The growth rate is at a maximum during this phase, and the population of cells are fairly uniform with respect to chemical composition and metabolic composition. 

The temperature of incubators must be uniform throughout and should not vary more than 0.2 C. The vegetative assay organism must be sensitive to the analyte, be stable (resistant to spontaneous change), be in the logarithmic growth phase (for uniformity of response), and be easily cultured, maintained and standardized. Spores suspension have similar criteria except that the spores must be capable of germinating with reasonable synchrony. 

A mathematical model of the fermentation of the bacterium Pseudomonas ovalis, which produces gluconic acid, has been developed (Rai Constantinides, AIChE Symposium Series 69 No 132, 114, 1973). This model which describes the dynamics of the logarithmic growth phase is summarized as follows. 

Maintain Raji cells in RPMI-1640/10% fetal calf syndrom (FCS) in a humidified 37°C, 5% C02 incubator. Before the day of electroporation, dilute the culture 3X to ensure that the cells are in logarithmic growth phase. 

Suspension cells should be transfected when they are in the logarithmic growth phase which is generally, 106-107 cells per mL. It is important to avoid extra pipetting or unnecessary washing steps. Do not vortex cells. 

For this purpose, an 18-hour-old nutrient broth culture of a bacterium sensitive to a particular phenothiazine was used. 2 ml of this 18-hour-old broth culture was added to 4 ml of a fresh broth. This was incubated at 37 °C for 2 h, so that the bacterial culture could attain the logarithmic growth phase. At this point, the number of viable cells in the culture was determined by the colony forming unit (CFU) count, as described by Miles and Misra [65]. The drug was added at a concentration higher than the respective MIC value at the logarithmic growth phase of the culture. The CFU counts were determined at intervals of 2 h, 6 h and then after 18 h. 

The MIC of thioridazine with respect to Staphylococcus aureus ML 322 was 200 pg/ml. At the logarithmic growth phase of the culture, when CFU count was 7.6 x 108, 400 xg/ml of the drug was added. After 2 h there were no five cells in the culture, proving severe bactericidal action of thioridazine on Staphylococcus aureus (Fig. 3). Similar action was observed when the drug... 

A cell suspension culture of T. dipterocarpum produced berberine (0.4 g/L) as the major alkaloid. The production of berberine was markedly stimulated by NAA in combination with 6-benzylaminopurine. Berberine was released into the culture medium during the logarithmic growth phase, but afterwards the alkaloid that was produced accumulated in the cells [152]. 

Nifurprazine has a bactericidal action against micro-organisms in the logarithmic growth phase as well as in the stationary phase > . A 50 per cent content of human serum in the culture medium does not interfere with the bactericidal activity of the compound. Further clinical investigations showed that the compound is very effective against wound infections and a preparation for topical application was marketed in 1966. 

---