Chapter 6: Microbial Growth

Question 1

How do bacteria divide?

Answer 1

By binary fission

Question 2

What does cell division require?

Answer 2

DNA replication: complete, exact copy of chromosome.

Question 3

How does binary fission occur?

Answer 3

• chromosomes attach to membrane
• membrane growth: chromosomes move apart
• septum formation: new membrane and wall material start growing through midsection of cell
• formation of two cells: membrane and wall material deposited at the cell midsection divide the cytoplasm in two

Question 4

Phases of growth

Answer 4

• Lag phase
• exponential (log) phase
• stationary phase
• death phase

Question 5

Phases of growth: lag phase

Answer 5

Adjustment to new conditions, few cells, little or no growth.

Question 6

Phases of growth: exponential (log) phase)

Answer 6

Logarithmic growth, most growth, live cells.

Question 7

Phases of growth: stationary phase

Answer 7

Cells undergo changes to survive, live and dead cells, no growth.

Question 8

Phases of growth: death phase

Answer 8

Cells begin to die.

Question 9

Continuous culture: chemostat

Answer 9

• concentration of limiting nutrient
• continuous: addition of nutrients , removal of waste-products
• cell number remains constant

Question 10

Colony growth

Answer 10

• mass of cells
• on laboratory medium
• not same as in natural environment
• used to study characteristics of microorganisms

Question 11

Biofilms

Answer 11

• natural environment
• complex mix of microorganisms
• unique interactions and impact on other microorganisms

Question 12

Classification by nutrition: heterotrophs

Answer 12

Different feeders. Organic compounds as source of carbon.

Question 13

Classification by nutrition: autotrophs

Answer 13

Self-feeders. CO2 as source of carbon.

Question 14

Classification by nutrition: chemotrophs

Answer 14

Chemical feeders. Derive both carbon and energy from organic compounds.

Question 15

Classification by nutrition: phototrophs

Answer 15

Light feeders. Energy from light.

Question 16

Example of a chemoautotroph

Answer 16

Methanogens

Question 17

Physical requirements for microbial growth

Answer 17

Temperature
pH
Osmotic pressure

Question 18

Chemical requirements of microbial growth

Answer 18

Carbon
Nitrogen, sulfur, and phosphorus
Trace elements
Oxygen

Question 19

What are the direct methods to measure microbial growth?

Answer 19

Plate count
Filtration
Most probable number
Direct microscopic count

Question 20

What are indirect methods of measuring microbial growth?

Answer 20

Turbidity
Metabolic activity
Dry weight

Question 21

At what pH do most bacteria like to grow?

Answer 21

Between 6.5 and 7.5

Question 22

At what temperature would a human pathogen likely grow? What type of microbe is it?

Answer 22

About 37 C, mesophile.

Question 23

What happens to a cell when placed in a hypotonic solution?

Answer 23

The cell will swell and possibly burst. A hypotonic solution has a greater concentration outside of the cell.

Question 24

What happens when a cell is placed in a hypertonic solution?

Answer 24

The cell will shrink. A hypertonic solution has a lower concentration outside of the cell.

Question 25

What happens when a cell is placed in an isotonic solution?

Answer 25

The cell will be in homeostasis. The concentration is the same inside and outside of the cell.

Question 26

How can bacteria be enumerated?

Answer 26

``` Turbidity Direct cell count Automated devices such as coulter counter Flow cytometer Real-time PCR ```

Question 27

How to check turbidity of bacteria?

Answer 27

Using a spectrophotometer. Measures the absorbance of light by cells in broth culture. The greater the turbidity, the larger the population size.

Question 28

Direct cell count method

Answer 28

Counts the total dead and live cells in a microscopic slide containing a pre measured grid.

Question 29

How does a coulter counter work?

Answer 29

Uses an electronic sensor to detect and count the number of cells.

Question 30

What is generation time?

Answer 30

The time required for a complete division cycle.

Question 31

Length of the generation time is a measure of

Answer 31

The growth rate

Question 32

What are used to define the numbers of bacteria after growth?

Answer 32

Exponentials

Question 33

Psychrophiles

Answer 33

An organism that grows best at about 15 degrees C, does not grow above 20 degrees C. Cold-loving microbe.

Question 34

Mesophiles

Answer 34

An organism that grows beaten about 10 degrees C and 50 degrees C. Moderate-temp-loving microbe Best at about 37 C

Question 35

Thermophiles

Answer 35

An organism whose optimal growth temperature is between 50 degrees C and 60 degrees C, a heat-loving-microbe

Question 36

What is the most common type of microbe?

Answer 36

Mesophiles.

Question 37

Extreme or hyperthermophiles

Answer 37

Have an optimum growth temperature of 80 C or higher.

Question 38

Acidophiles

Answer 38

A bacteria that grows slow pH 4

Question 39

Plasmolysis

Answer 39

Loss of water from a cell in a hypertonic environment

Question 40

Halophile

Answer 40

An organism that grows in or can tolerate saline conditions.

Question 41

Plate count

Answer 41

Most frequently used method of measuring bacterial population Inoculate plate with a sample and count number of colonies

Question 42

Filtration

Answer 42

Used to measure small quantities of bacteria

Question 43

Most probable number

Answer 43

Used mainly to measure bacteria that will not grow on solid medium Dilute a sample repeatedly and inoculate several broth tubes for each dilution point Count the number of positive tubes in each set

Question 44

Direct microscopic count

Answer 44

Stain is added to visualize bacteria | Cells are counts and multiplied by a factor to obtain concentration.

Question 45

Obligate anaerobes(strict)

Answer 45

Bacteria that cannot grow in the presence of oxygen

Question 46

Aerotolerant anaerobes

Answer 46

Cannot use oxygen for growth but can tolerate its presence.

Question 47

Facultative anaerobes

Answer 47

Can grow without oxygen but use oxygen if it is present

Question 48

Microaerophile

Answer 48

Requires oxygen to survive but requires environments containing lower levels of oxygen than are present in the atmosphere

Question 49

Alkalinophile

Answer 49

Prefers or is able to withstand an alkaline environment, pH above 9

Question 50

Strict aerobe (obligate)

Answer 50

Requires oxygen to grow

Question 51

What is quorum sensing?

Answer 51

The ability of bacteria in a biofilm to communicate with each other and coordinate their activities.

Question 52

The microbes in biofilms can work

Answer 52

Cooperatively to carry out complex tasks

Question 53

Phagocytosis

Answer 53

The ingestion of bacteria or other material by phagocytes and amoeba is protozoans

Question 54

Pinocytosis

Answer 54

The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane