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Microbial Growth

الكلية كلية الهندسة     القسم  الهندسة البيئية     المرحلة 1
أستاذ المادة اشواق مخيف سلمان حبيب الجبوري       11/07/2018 19:49:42
Microbial Growth:
Refers to an increase in cell number, not in cell size.Bacteria grow and divide by binary fission, a rapid and relatively simple process.

The stages of a typical growth curve (figure below) are:
1. Lag phase: When the cells are adjusting to their new environment. During thisphase, cellular metabolism is accelerated, resulting in rapid biosynthesis ofcellular macromolecules, primarily enzymes, in preparation for the next phase ofthe cycle. Although the cells are increasing in size, there is no cell division andtherefore no increase in numbers.
2. Logarithmic (log)/Exponential phase: Under optimum nutritional and physical conditions, the physiologically robust cells reproduce at a uniform and rapid rate by binary fission. Thus there is a rapid exponential increase in population, which doubles regularly until a maximum number of cells is reached. The length of the log phase varies, depending on the organisms and the composition of the medium, although the average may be estimated to last 6 to 12 hours.
3. Stationary phase: During this stage occur:
-Population size begins to stabilize.
-Number of cells produced = Number of cells dying
-Overall cell number does not increase.
-Cell division begins to slow down.
-Factors that slow down microbial growth:
• Accumulation of toxic waste materials
• Acidic pH of media
• Limited nutrients
• Insufficient oxygen supply


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