Microbial growth

What is binary fission

An asexual process in which a single cell divides into two cells

• Occurs in prokaryotes

Binary fission process

1. The cell elongates, and DNA is replicated

2. Cell wall and plasma membrane begin to constrict

3. A cross wall forms, separating 2 DNA copies

4. Cells separate

What is a generation time

Time it takes for a cell to divide

• Ranges from 15 minutes to 24 hours

• Depends on species and conditions

Bacteria growth is exponential, what does that mean?

Exponential growth formula

Generation time = Growth time (minutes) / number of generations

E.g. E. coli went through 3 generations of growth in the span of 1 hour. The generation time was calculated by 60 mins/ 3 generations = 20 minutes of generation time

Generation time for E.coli

20 minutes but depends on nutrients available

Generation time for mycobacterium tuberculosis

15-20 hours but depends on nutrients available

What are the phases of bacterial growth

Lag, Log, Stationary, and Death phase. They are detected by the count of viable (live) cells.

What happens during lag phase

1st phase

Delay in growth occurs while cells adjust to their new environment

what happens during log phase

2nd phase

Period of rapid exponential growth

What happens during stationary phase

3rd phase

Nutrients are depleted; waste accumulates

Population growth RATE levels off

What happens during the death phase

4th phase

Waste builds up, and nutrients continue to deplete

Cells begin to die

The rate of death is exponential (rapid)

A small number of cells adapt to the waste, and they feed off dead cells

How does temperature affect microbe’s environment

It can decrease or speed up enzymatic reactions and increase growth rates at increased temperatures. However, temperature too high can cause the cell’s proteins to denature

Optimal temperatures for Psychrophiles

-20 C and 10 C

Optimal temperatures for psychrotrophs

0-30 C

Associated w/foodborn illness

Optimal temperatures for Mesophiles

10-50 Celsius

Associated with most pathogens

Optimal temperatures for Thermophiles

40-75 C

Associated w/compost piles and hot springs

Optimal temperatures for Hyperthermophiles

Extreme thermophiles

65-120 C

Danger zone or temperatures at which to store food

15-50 C as bacteria grows rapidly and produce toxins

Above 60 C destroys most microbes but is better to go w/low temps

Below 0 C (below freezing) is best for no growth

Why are hyperthermophiles that grow at temperatures above 100 C seemingly limited to the oceanic depths

Acidophiles

Grows at less than 1-5 pH

• Live in sulfur hot springs and volcanic vents

• Keep a neutral cytoplasmic pH

• Proton pumps expel excess protons from cytoplasm to raise pH (expels H molecules to make the cell more acidic)

Neutrophiles

Grow at 5-8 pH

• Most microorganisms fall within this range

Akaliphiles

Grow best at 9-11 pH

• Associated w/soda lakes

What is a halophile

Thrive in high-salt environments

• tolerate up to a 35%

• Associated w/the Dead Sea and Great Salt Lake of Utah

What are facultative halophiles

Tolerate higher salt than normal halophiles HOWEVER they make not grow well

• E.g. Staphylococcus Aureus

How does osmotic pressure affect bacteria

The bacterial cytoplasm made up of 80% water

• If the cell enters a surrounding with higher concentration than their own, through osmosis the water will move out of the cell and make the cell appear as wilted or collapsed

• This process is called plasmolysis which can affect bacteria by reducing osmotic pressure

How is osmotic pressure used in food preservation

What are organic growth factors

Organic molecules that the cell cannot synthesize and that must be obtained from their environment to support growth

• E.g. Amino acids, vitamins, peptides, etc.

Aerotolerant anaerobes

Tolerate O2 but don’t use it in their metabolic process

• Can deactivate ROS

How does Oxygen affect obligate anaerobes

They do not use oxygen in their metabolic processes

• When exposed to oxygen, they can form Reactive Oxygen Species (ROS) that poison the bacteria and cause it to die as proteins and DNA are damaged

Obligate aerobes

Absolute dependence on O2

• Can manage and deactivate ROS

Microaerophiles

Use only small amounts of O2

• Can deactivate ROS but in low amounts

Facultative anaerobes

Grow w/ and w/o O2

• Can switch between using O2 and fermentation

• Can deactivate ROS

How do obligate, facultative, aerotolerant, and microaerophiles survive toxic forms of oxygen

What are biofilms

Structures made by bacteria to ADHERE to a surface, making it difficult to treat.

• Reside in indwelling devices like catheters and heart valves

How are biofilms formed

Why are biofilms important to microbes?

What is the medical importance of biofilms

What are the characteristics of agar

Chemically defined media

Complex media

Reducing media

Selective medium

Differential medium