MICR101A_5_Bacterial Growth

Physical Requirement for Growth

• Temperature

• pH

• Osmotic pressure

Chemical Requirements for Growth

• Carbon

• Nitrogen

• Sulfur

• Phosphorus

• Oxygen

Psychrophiles

cold-loving microbes, capable of growing at 0°C

Psychrophiles

cannot grow above 40°C

Psychrophiles

optimum growth temp. is 20-30°C

Psychrophiles

Found mostly in the ocean’s depth or polar regions

Psychrophiles

known as “spoilage microorganisms”

Mesophiles

moderate-temperature-loving microbes

Mesophiles

most common type of microbe

Mesophiles

Optimum temperature is about 37°C

Thermophiles

heat-loving microbes

Thermophiles

Optimum temperature is at 50-60°C

Thermophiles

not considered a public health concern

Thermophiles

important in organic compost piles

Hyperthermophiles

“Extreme Thermophiles”

Hyperthermophiles

optimum growth temperature of 80°C

pH 6.5 and 7.5

Most bacteria grow best in a narrow pH range near neutrality, between ____ and ____

Acidophiles

microorganisms that are tolerant of acidity

Halophiles

can adapt to high salt concentrations

Anaerobes

bacteria that are unable to use molecular oxygen for energy-yielding reactions

Example of Anaerobes

Clostridium

Obligate aerobes

organisms that require oxygen to live

Facultative anaerobes

can use oxygen when it is present but are able to continue growth by using fermentation or anaerobic respiration when oxygen is not available

example of Facultative anaerobes

E.coli

Aerotolerant anaerobes

fermentative and cannot use oxygen for growth, but they tolerate it fairly well

Microaerophiles

they grow only in oxygen concentrations lower than those in air.

Generation time

the time required for a cell to divide

PHASES OF GROWTH

• Lag Phase

• Log Phase/ Exponential Growth Phase

• Stationary Phase

• The Death Phase/ Logarithmic Decline Phase

Lag Phase

period of little or no cell division

Lag Phase

can last for 1 hour or several days

Lag Phase

cells are not dormant

Lag Phase

period of intense metabolic activity such as synthesis of enzymes

Log Phase/ Exponential Growth Phase

cells begin to divide and enter a period of growth or logarithmic increase

Log Phase/ Exponential Growth Phase

cellular reproduction is most active

Log Phase/ Exponential Growth Phase

generation time reaches a constant minimum

Stationary Phase

the growth rate slows

Stationary Phase

number of microbial deaths balances the number of new cells

Stationary Phase

period of equilibrium

Stationary Phase

the population exceeds the carrying capacity and run out of nutrients and space

The Death Phase/ Logarithmic Decline Phase

number of deaths exceeds the number of new cells formed

The Death Phase/ Logarithmic Decline Phase

the population is diminished to a tiny fraction of the number of cells or until the population dies out entirely