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BATCH CULTURE

Definition

A form of culture in which a given volume of liquid medium is inoculated with cells (e.g. bacteria,unicellular algae) capable of growth in that medium, and the inoculated medium is incubated for an appropriate period of time. Cells growing under these conditions are exposed to a continually changing environment caused by the gradual consumption of nutrients and the accumulation of metabolic wastes, among other factors. The growth curve obtained by monitoring a batch culture commonly exhibits a sequence of four main phases of growth. In the lag phase, the growth rate (the rate of increase in cell numbers or biomass) is initially minimal but subsequently rises to a value dictated by the prevailing conditions (e.g., temperature, concentration of nutrients, etc.). The length of the lag phase is influenced by the cultural history of the cells in the inoculum. For example, if slowly dividing cells from a nutrient-poor environment are transferred to a nutrient-rich medium which can support a higher rate of growth, there is usually a relatively long lag phase during which time the cells become adapted to the new environment; during this period of adaptation the cells exhibit unbalanced growth. Subsequently, growth occurs at a new, higher rate permitted by the higher levels of nutrients. At the end of the lag phase, the cells enter the exponential (= logarithmic or log ) phase of growth in which, for a given organism, the growth rate is both constant and maximal for the particular growth conditions. In this phase there is an exponential increase in cell numbers and biomass; this type of growth is referred to as balanced growth. In the stationary phase the growth rate declines and eventually reaches zero. In the death phase the number of viable cells in the culture (maximal in the stationary phase) declines.

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