Microbial Growth Requirements: Temperature, pH, Osmotic Pressure, and Nutrients

physical requirements for microbial growth?

Temperature

pH

Osmotic pressure

chemical requirements for microbial growth?

Carbon

Nitrogen

Sulfur

Phosphorus

Trace elements

Oxygen

Organic growth factors

What are the minimum, optimum, and maximum growth temperatures?

Minimum - lowest temperature where growth occurs

Optimum - temperature where growth is fastest

Maximum - highest temperature where growth can occur

Psychrophiles

cold-loving

Psychrotrophs

grow in refrigerator temperatures; spoil food

Mesophiles

moderate temperatures; most human pathogens

Thermophiles

heat-loving

Hyperthermophiles

grow at extreme high tempertures

bacteria grow at? (pH)

6.5-7.5

Molds & yest

pH 5-6

Acidophiles grow in?

acidic environments

Alkaliphiles grow in?

basic environments

What happens to bacteria in a hypertonic environment?

Water leaves the cell

causes plasmolysis (cell shrinks)

Growth is inhibited

extreme (obligate) vs faculative halophiles:

Extreme (obligate) halophiles: require high osmotic pressure

Facultative halophiles: tolerate high osmotic pressure but don't require it

Why do microorganisms need carbon?

- Carbon is the structural backbone of organic molecules.

- Chemoheterotrophs obtain carbon from organic compounds.

- Autotrophs use carbon dioxide (CO₂).

Why do microorganisms need nitrogen?

Nitrogen is needed to make:

• Proteins

• DNA

• ATP

Most bacteria obtain nitrogen by breaking down proteins.

Some use ammonia, and a few perform nitrogen fixation.

Why are sulfur and phosphorus important?

Sulfur

• Used to make amino acids

Phosphorus

• Needed for DNA

• RNA

• ATP

• Cell membranes

what are trace elements?

small