Chapter 4

Question 1

Microbial growth:

Answer 1

Increase in number of cells, not cell size. Growth in population size.

Question 2

Colony-forming units:

Answer 2

On plate counts. Visible bacterial colonies on solid media.

Question 3

Serial Dilutions:

Answer 3

Used for plate counting, used to decrease a bacterial concentration to a required concentration for a specific test method, or to a concentration which is easier to count when plated to an agar plate.

Question 4

Turbidity:

Answer 4

Most common method of cell counting.
Measured with a Spectrophotometry: Bacteria scatter light, based on their density, measured as optical density (OD), OD correlated with biomass and counts from viable counts. Only absorbance needs to be measured (very rapid).
Percentage of transmission
Used for large amounts of bacteria, need 10 million to 100 million cells per milliliter to read – not for detecting contaminants

Question 5

Endospores:
Sporulation:
Germination:

Answer 5

Resting cells; produced when nutrients are depleted, resistant to desiccation, heat, chemicals, and radiation. Readily spread.
Produced by Bacillus and Clostridium

Sporulation: endospore formation
Germination: spore returns to vegetative state
NOT REPRODUCTION

Question 6

Balanced Growth:

Answer 6

All cells constituents increase by the same proportion over any given interval of time

Question 7

Chemostat:

Answer 7

Growth rate determined by addition of medium
Cell density is constant, limiting nutrient. Used for performing long experiments- good for studying evolution of microbes. Large scale industrial fermentations.

Question 8

Extremophiles:

Answer 8

Thrive under extreme conditions.
Temperature, hydrostatic pressure, osmotic pressure, pH, oxygen, radiation.

Question 9

Plasmolysis:

Answer 9

Caused by hypertonic environments, or an increase in salt or sugar.

Plasmolysis is the process in which cells lose water when they are placed in a hypertonic solution. It causes contraction or shrinking of the plasma membrane away from the cell wall. It is a reversible process and the cell can get back to normal when placed in a hypotonic solution

Question 10

Determining cell numbers: Counting of cells and determination of mass/density of the cell

Answer 10

Counting microbial cells:
direct counting (microscope), flow cytometer, viable counts (spread plate, pour plate), filtration.
Determining mass/density:
weighing, spectrophtometry (turbidity).

Question 11

Direct count of cells:

Answer 11

Microscope and counting chamber. Requires dense cultures, number of cells per unit area (proportional to volume), counts both living and dead cells.

Question 12

Flow cytometer for counting cells:

Answer 12

Faster and automated. Total particle count. Counts and analyzes the size, shape, surface topography, internal complexity, sorts. Counts living and dead cells.

Question 13

Viable counts:
Spread plate and Pour plate

Answer 13

Uses serial dilutions, plated on medium to get 30 to 300 colonies per plate. Allows for calculation of number of cells per ml based on dilution.

Question 14

Plate counts:

Answer 14

Takes 24 or more hours, only counts viable cells, colony forming units, 30-300 colonies.

Question 15

Membrane Filtration for counting bacteria:

Answer 15

For small quantity of bacteria (like in lakes or relatively pure streams). Water passed through a thin membrane filter

Question 16

Cell weight:

Answer 16

For mold and filamentous bacteria, direct weighing of dried cell mass (removed from media, dried, weighed).

Question 17

Four Basic phases of bacterial growth:

Answer 17

1. Lag; initially no increase in cell numbers, synthesis of new enzymes required for growth.
2. Exponential; number of cells double each division.
3. Stationary; Slowed growth rate, nutrients exhausted. waste products accumulate, other conditions not optimal for growth (growth=death).
4. Death; cells die due to accumulation of toxins. Death exceeds the number of new cells formed.

Question 18

What are the three equations of microbial growth?

Answer 18

Law of growth: N=(2^n)No

Generation number: logN-logNo/log2

Generation time: [g]=t/n

Question 19

Generation time:

Answer 19

Question 20

Minimum growth temperature, optimum growth temperature, maximum growth temperature:

Answer 20

• Minimum growth temperature – lowest temp at which the species will grow
• Optimum growth temperature – highest
  growth rate
• Maximum growth temperature – highest
  temp at which the species will grow

Question 20

What is the growth range of microbes?

Answer 20

-15 ºC to 121 ºC.
Basically any condition with liquid water.

Question 21

Psychrophiles

Answer 21

Typically grow at 5ºC
Psychrophiles exist at lower to extreme low temperatures, ranging from 5°C to 15°C or lower. It can grow even up to the freezing point of water. They are found in freezing environments, such as glaciers, deep oceans, and polar regions.

Question 22

The smaller the cell, the _ it grows

Answer 22

The faster it grows.

Question 23

Mesophiles:

Answer 23

Typically grows at 37ºC.
Mesophiles are microorganisms which grow at moderate temperatures between 20 °C and 45 °C and with an optimum growth temperature in the range of 30–39 °C. They are isolated in both soil and water environments; species are found in the Bacteria, Eukarya, and Archaea kingdom

Question 24

Thermophiles:

Answer 24

Typically grow between 60º and 80ºC

Question 25

Hyperthermophiles:

Answer 25

Typically grow at temperatures 80ºC and higher.

Question 26

Three types of adaptations for high-temperature (Hyper)Thermophiles:

Answer 26

1. Protein stability; charged amino acids on surfaces, heat shocked proteins and chaperones
2. DNA stability; positive supercoiled DNA, DNA-binding proteins and relatively high magnesium
3. Membrane stability; special archaea lipid membranes (isoprenoids, ether bonds, bilayer or monolayer)

Question 27

Food preservation and sterilization:

Answer 27

Question 28

Hydrostatic Pressure (two types and three modifications):

Answer 28

Barotolerant: can grow at high pressures.
Barophiles/Piezophiles: needs high pressures.

Modifications:
Membranes - unsaturated fatty acids
Proteins- pressure resistant and chaperones
DNA- negative supercoiling

Question 29

Osmotic Pressure (two types and what is it used in):

Answer 29

• Microorganisms obtain almost all of their nutrients from the surrounding water
  – Composed of 80-90% water
• High osmotic pressures remove necessary water from the cell

Extreme or obligate halophiles: require high osmotic pressure. Cell must be in hypertonic solution.
Facultative halophiles: tolerate high osmotic pressure. Able to grow at high salt concentrations.
Used in food preservation.

Question 30

pH Range (two types and common pH ranges):

Answer 30

Acidophiles: pH below 5 (some at pH 0).
Alkalophiles: pH 8.5 to 11.5
Most bacteria maintain narrow pH range (7.4-7-8). Below pH 4, little to no growth. Molds and yeasts grow best at a more acidic pH

Question 31

Obligate aerobes:

Answer 31

Require oxygen to live.

Question 32

Facultative anaerobes:

Answer 32

Can use oxygen when present, but are able to continue growth by using fermentation or anaerobic respiration when oxygen is unavailable.

Question 33

Obligate anaerobes:

Answer 33

Unable to use oxygen and oxygen may be toxic.

Question 34

Microaerophiles:

Answer 34

Aerobic, but require less oxygen than in the air.

Question 35

Toxicity of Oxygen:

Answer 35

superoxide radical, hydrogen peroxide, and hydroxyl radical: oxidizing agents that destroy cell components

O2 tolerance requires enzymes like catalase and superoxide dismutase - to reduce toxic oxygen compounds.

Obligate anaerobes lack these enzymes.

Question 36

Superoxide dismutase (SOD):

Answer 36

Converts superoxide radicals to molecular oxygen and hydrogen peroxide.

Question 37

Catalase:

Answer 37

Converts hydrogen peroxide to water and oxygen.

Question 38

Radiation:

Answer 38

Damages cells: cleaving bonds, forming abnormal bonds, generates O2 radicals. Some bacteria are very resistant, like Deinococcus radiodurans.
Adaptations: has multiple chromosome copies, extensive DNA repair systems.

Question 39

Steps in Binary Cell Division:

Answer 39

Doublining of protoplasm: living content of a cell surrounded by plasma membrane, including chromosome.
Then the cell diviids into two:
Gram-negative (constriction of their envelope layers at midcell) and gram-postive (division septum formed).
Divided symmetrically into two halves.

Question 40

Two alternatives to binary fission:

Answer 40

1. Budding (a new organism develops from a bud of an existing organism).
2. Progeny cells do not always separate from one another, but stick together.