Microorganisms' Growth
Chapter 6
Microbial Growth
1
Growth
• increase in cellular constituents that may result in: – increase in cell number
• e.g., when microorganisms reproduce by budding or binary fission – increase in cell size
• e.g., coenocytic microorganisms have nuclear divisions that are not accompanied by cell divisions
• microbiologists usually study population growth rather than growth of individual cells
2
The Growth Curve
• observed when microorganisms are cultivated in batch culture
– culture incubated in a closed vessel with a single batch of medium
• usually plotted as logarithm of cell number versus time
• usually has four distinct phases
3
population growth ceases
maximal rate of division and population growth
decline in population size
no increase
Figure 6.1
4
Lag Phase
• cell synthesizing new components
– e.g., to replenish spent materials
– e.g., to adapt to new medium or other conditions
• varies in length
– in some cases can be very short or even absent
5
Exponential Phase
• also called log phase
• rate of growth is constant
• population is most uniform in terms of chemical and physical properties during this phase 6
cells are dividing and doubling in number at regular intervals
7
each individual cell divides at a slightly different time curve rises smoothly rather than as discrete steps Figure 6.3
8
Balanced growth
• during log phase, cells exhibit balanced growth – cellular constituents manufactured at constant rates relative to each other
9
Unbalanced growth
• rates of synthesis of cell components vary relative to each other
• occurs under a variety of conditions
– change in nutrient levels
• shift-up (poor medium to rich medium)
• shift-down (rich medium to poor medium)
– change in environmental conditions
10
Effect of nutrient concentration on growth Figure 6.2
11
Stationary Phase
• total number of viable
Microbial Growth
1
Growth
• increase in cellular constituents that may result in: – increase in cell number
• e.g., when microorganisms reproduce by budding or binary fission – increase in cell size
• e.g., coenocytic microorganisms have nuclear divisions that are not accompanied by cell divisions
• microbiologists usually study population growth rather than growth of individual cells
2
The Growth Curve
• observed when microorganisms are cultivated in batch culture
– culture incubated in a closed vessel with a single batch of medium
• usually plotted as logarithm of cell number versus time
• usually has four distinct phases
3
population growth ceases
maximal rate of division and population growth
decline in population size
no increase
Figure 6.1
4
Lag Phase
• cell synthesizing new components
– e.g., to replenish spent materials
– e.g., to adapt to new medium or other conditions
• varies in length
– in some cases can be very short or even absent
5
Exponential Phase
• also called log phase
• rate of growth is constant
• population is most uniform in terms of chemical and physical properties during this phase 6
cells are dividing and doubling in number at regular intervals
7
each individual cell divides at a slightly different time curve rises smoothly rather than as discrete steps Figure 6.3
8
Balanced growth
• during log phase, cells exhibit balanced growth – cellular constituents manufactured at constant rates relative to each other
9
Unbalanced growth
• rates of synthesis of cell components vary relative to each other
• occurs under a variety of conditions
– change in nutrient levels
• shift-up (poor medium to rich medium)
• shift-down (rich medium to poor medium)
– change in environmental conditions
10
Effect of nutrient concentration on growth Figure 6.2
11
Stationary Phase
• total number of viable