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nutrition
process by which chemical substances (nutrients) are acquired from the environment and used for cellular activities

essential nutrients
must be provided to an organism

Two categories of essential nutrients
macronutrients
micronutrients or trace elements

macronutrients
 required in large quantities; play principal roles in cell structure and metabolism
 •proteins, carbohydrates

micronutrients or trace elements
–required in small amounts; involved in enzyme function and maintenance of protein structure
•manganese, zinc, nickel

Microbial Growth
•Increase in cell number
•Populations increase at very rapid rates
 •Colonies of bacteria contain billions
 of cells
•Method of growth: Binary fission
•Typical growth rates: 2030 minutes

Bacterial Growth Rates
 Each new fission cycle increases the population by a factor of 2 – exponential or logarithmic
 growth.

Generation, or doubling time
Time required for a complete fission cycle
 Each new fission cycle increases the population by a factor of 2 – exponential or logarithmic
 growth.

Generation time
• Time required for population to double
• Typical generation time: 20 min

Equation for calculating population size over time
N^ƒ = (N^i)2^n
N^ƒ is total number of cells in the population.
N^i is starting number of cells.
Exponent n denotes generation time.
2^n number of cells in that generation

Lag phase
Cells are not dividing
They are getting use to the environment
They are preparing

Log phase
Cells are metabolically active
Vulnerable to antibiotics and radiation
Cells are dividing

Stationary phase
Number of cells and number of live cells are equal

Death phase
Number of dead cells is greater than number of live cells

Measuring Bacterial Growth: Direct Chamber
Counting Chamber: the slide has a grid
Cheap and fast to use

Viable Count
–Plate count method  counts colonies, 12 hours; gives an accurate estimate of the number of viable cells
–Filtration
–Most probable number (MPN)

Which method would give you the highest
estimate, a direct count or viable count?
Viable

Minimum temperature
• lowest temperature that permits a microbe’s growth and metabolism

Maximum temperature
• highest temperature that permits a microbe’s growth and metabolism

Optimum temperature
• promotes the fastest rate of growth and metabolism

Psychrophiles
1.optimum temperature below 15oC; capable of growth at 0oC

Mesophiles
1.optimum temperature 20o40oC; most human pathogens

Thermophiles
1.optimum temperature greater than 45oC

