Growth and Cell Division Microbial Growth Defined:1. Mother or parent cell doubles in size2. Divides into two daughter cells Microbial growth is defined as the increase in the number of cells, which occurs by cell division
Cell Division Binary fission (equal cell division): A cell duplicates its components and divides into two cells Septum: A partition that grows between two daughter cells and they separate at this location Budding (unequal cell division): A small, new cell develops from surface of exisiting cell and subsequently separates from parent cell
Phases of Growth Consider a population of organisms introduced into a fresh, nutrient medium Such organisms display four major phases of growth1. The lag phase2. The logarithmic phase3. The stationary phase4. The death phase
The Lag Phase Organisms do not increase significantly in number They are metabolically active Grow in size, synthesize enzymes, and incorporate molecules from medium Produce large quantities of energy in the form of ATP
The Log Phase Organisms have adapted to a growth medium Growth occurs at an exponential (log) rate The organisms divide at their most rapid rate a regular, genetically determined interval (generation time)
Stationary Phase:1. Cell division decreases to a point that new cells are produced at same rate as old cell die.2. The number of live cells stays constant. Decline (Death) Phase:1. Condition in the medium become less and less supportive of cell division2. Cell lose their ability to divide and thus die3. Number of live cells decreases at a logarithmic rate
Growth in Batch Culture Growth is generally used to refer to the acquisition(perolehan) of biomass leading to cell division, or reproduction A “batch culture” is a closed system in broth medium in which no additional nutrient is added after inoculation of the broth
Growth in Continuous Culture A “continuous culture” is an open system in which fresh media is continuously added to the culture at a constant rate, and old broth is removed at the same rate. This method is accomplished in a device called a chemostat. Typically, the concentration of cells will reach an equilibrium level that remains constant as long as the nutrient feed is maintained.