Microbial Growth and Its Control Lesson 2 Flashcards
increase in number not size
Microbial Growth
Binary Fission
- Cell elongates and DNA is replicated
- Plasma membrane begins to constrict and new wall is made
- Cross-wall forms, completely separating the two DNA copies
- Cell separate
time required for a cell to divide (and its population to double)
Generation Time
Phases of Growth
- Lag Phase
- Log Phase
- Stationary Phase
- Death Phase
The Requirements for Microbial
Growth
Physical Requirements
Chemical Requirements
Physical Requirements
◦ Temperature
◦ pH
◦ Osmotic pressure
Chemical Requirements
◦ C
◦ N, S, P
◦ Trace elements
◦ O2
◦ Organic growth factors
Temperature in this range destroy most microbes, although lower temperatures take more time
60-130 C
Very slow bacterial growth
50-60 C
Rapid growth of bacteria; some may produce toxins
15-55 C
Many bacteria survive; some may grow.
-5 - 15 C
Refrigerator temperatures; may allow slow growth of spoilage bacteria, very few pathogens
0-5 C
No significant growth below freezing
0 to -30 C
PH
most bacteria– 6.5-7.5
◦ cultured bacteria produce acids that inhibit own growth; hence, buffers are used
acidophiles– even up to 1
fungi– wider range, usually 5-6
Osmotic Pressure
High osmotic pressure (hypertonic) → plasmolysis (shrinkage)
◦ adding salt can preserve food
Low osmotic pressure (hypotonic) → swelling
Extreme halophiles– can grow at high salt concentrations
- plasmolysis (shrinkage)
- adding salt can preserve food
High osmotic pressure (hypertonic)
swelling
Low osmotic pressure (hypotonic)
can grow at high salt concentrations
Extreme halophiles
- the structural backbone of living matter
- half the dry weight of bacterial cell
Carbon
