Lecture 5: Microbial Growth

Question 1

What is Cell growth?

Answer 1

Increase in cell number

-Growth = reproduction

Question 2

What is binary fission?

Answer 2

Division of 1 cell into 2 cells

-Divides through elongation and septum formation

Question 3

What is generation time?

Answer 3

Time required for binary fission

-30min to 6hrs typically

Question 4

What factors affect generation time?

Answer 4

Environmental Factors
-Nutrient availability and temperature

Genetic Factors
-Specific to different microbial species

Question 5

What is the Divisome?

Answer 5

Collection of FTS Proteins embedded in cytoplasmic membrane that direct cell division in prokaryotes

Question 6

What does FTS stand for?

Answer 6

Filamenting Temperature Sensative

Question 7

What proteins make up the Divisome?

Answer 7

FtsZ
ZipA
FtsA
Ftsl

Question 8

What does the FtsZ protein do?

Answer 8

Forms ring around center of the dividing cell

-Related to tubulin

Question 9

What does the ZipA protein do?

Answer 9

Connects FtsZ ring to Cytoplasmic Membrane

-The “Anchor”

Question 10

What does the FtsA protein do?

Answer 10

Attracts the other Fts proteins to form the divisome

-The “Recruiter”

Question 11

What does the Ftsl Protein do?

Answer 11

Peptidoglycan synthesis
-Synthesizes peptidoglycan for the newly formed cell walls in order to complete separation

Good for new antibiotics or Drug design
-Target this (Or any) protein = prevent bacterial growth

Question 12

What is the MreB protein?

Answer 12

Part of cell morphology
-Forms cellular cytoskeleton

Absent in Coccoid bacteria
Present in Rod-shaped bacteria

Question 13

What kind of growth does a microbial population experience? What are the applications of this?

Answer 13

Exponential growth

• Cells double EACH generation (1->2->4->8 etc)
• So the rate increases each generation

Applicable to standards for bacterial counts in food

Question 14

What are the different phases of the growth cycle for a bacterial population in a CLOSED SYSTEM (No nutrients in and No waste products out)?

Answer 14

Lag Phase
Exponential Phase
Stationary Phase
Death Phase

Question 15

What is the lag phase of microbial growth?

Answer 15

Low (but positive) growth rate

-Recovering from transfer to nutrient agar (lab conditions but also wild)

Question 16

What is the Exponential Phase of Microbial Growth?

Answer 16

Big jump in growth rate

-Maximal rate, all cells dividing

Question 17

What is the Stationary Phase of Microbial growth?

Answer 17

Net Growth rate = 0
-Nutrients begin depleting and waste products accumulating

Also known as “Cryptic Growth”
-# of cells dividing = # of cells dying

Question 18

What is the death phase of microbial growth?

Answer 18

Growth Rate Negative

Question 19

What is a Continuous Culture? What is an Example?

Answer 19

Continuous Culture is an open system

Example is Chemostat

• Nutrient Rich broth in
• Waste products out

Question 20

What are some controls and applications of a continuous culture?

Answer 20

Controls

• Dilution rate (How fast in/out)
• Nutrient concentration

Applications
-Ecology and physiology

Question 21

What are the methods for measuring microbial growth?

Answer 21

Microscopic Counts
-Cell counts (Both living/dead)

Viable Counts

• Plate counts (living)
• # of colonies that form = # of cells in sample

Question 22

What are the advantages/disadvantages of Microscopic Counts for measuring microbial growth?

Answer 22

Advantages
-Simple method

Disadvantages

• Counts living/dead
• Difficult with low cell number and/or motile cells

Question 23

What are the advantages/disadvantages of Viable Counts for measuring microbial growth?

Answer 23

Advantages

• High sensitivity
• Counts only viable cells

Disadvantages
-Possible errors (Cell clumps, plating inconsistencies)

Question 24

What is the Turbidimetric Method for measuring Microbial growth?

Answer 24

Using light shined through vials with sample and measuring with spectrophotometer
-Cell mass = Cell Number

Question 25

What are the advantages/disadvantages for using the Turbidimetric method for measuring microbial growth?

Answer 25

Advantages - Simple method - Non-destructive (don't have to throw away sample) Disadvantages -Possible errors (cell clumps + Biofilms)

Question 26

What are the cardinal temperatures?

Answer 26

Minimum: below this temp = no growth Optimal: at this temp = fastest growth Maximum: above this temp = cell death Differ for each species of microorganism - Limited Temp (25-40 degrees Celsius) - Proteins within each microbe function at specific temp

Question 27

What are the different temperature classifications for microbes that live in different environments?

Answer 27

``` Psychrophile = (< 15 degrees C) Mesophile = Moderate Thermophile = (> 45 degrees C) Hyperthermophile = (>80 degrees C) ``` Anything that isn't a Mesophile = Extremophile

Question 28

What kind of Microbe lives in the cold? Where are they found?

Answer 28

Psychrophiles - Slow growing in pockets of water - Deep Oceans, Glaciers, Polar Regions

Question 29

What kinds of molecular adaptations have Psychrophioles developed for their environment?

Answer 29

Cytoplasmic membrane contains much more Unsaturated/Short Chain Fatty Acids -This causes the membrane to be more loosely packed and fluid at low temperatures Cyroprotectants - Cold Shock Proteins - Antifreeze for cell - Ice that forms inside cell will cause PHYSICAL damage

Question 30

What kinds of Microbes live in hot/very hot temps? Where are they found?

Answer 30

Thermophiles and Hyperthermophiles -Hot springs, Surface Soils, Water Throwback to life on early earth

Question 31

What kinds of molecular adaptations have Thermophiles/Hyperthermophiles developed for their environment?

Answer 31

Cytoplasmic Membrane has more Saturated/Long Chain Fatty Acids -Provides more stability at high temps Heat Protectants -Heat Shock Proteins (chaperones - as protein begins to denature, holds it together) More Ionic Bonds

Question 32

What biotechnological applications have extremophiles played a role in?

Answer 32

Polymerase Chain Reaction (copying DNA) - Cyclical heating (denature) of DNA to 94 degrees C - Add in DNA Polymerase to add on new strand each cycle ``` Taq Polymerase (From Hot spring bacteria) -using this heat resistant DNA Polymerase from extremophile prevents you from having to add more DNA polymerase each cycle ```

Question 33

Is there an upper temperature limit for life?

Answer 33

So far ~125 degrees celsius - Above 100 degrees celsius only archaea live - As time passes we'll probably discover more that live at higher temps

Question 34

What other factors affect microbial growth besides temperature?

Answer 34

pH Water Oxygen

Question 35

What are the two types of microbes that live in different pH environments?

Answer 35

Acidophiles -Optimal growth < pH 5.5 Alkaliphiles -Optimal growth < pH 8

Question 36

How does Water availability affect microbial growth?

Answer 36

Water Amount -Moist vs dry habitat Dissolved Solutes in Water - Low vs High concentration of solutes in water - High solute concentration = dessication/water loss from microbial cell

Question 37

What are xerophiles, Osmophiles, Halophiles?

Answer 37

Xerophiles: Can grow in areas with low availability of water Osmophiles: Can grow in areas with high Osmotic Pressures (High sugar concentration) Halophiles: Can grow in areas with salt concentration

Question 38

What is an Aerobic Microorganism and what are the types?

Answer 38

Growth in the presence of oxygen Obligate Aerobe: Oxygen required, only aerobic respiration Facultive Aerobe: Oxygen not required but grows better with it. Aerobic/Anaerobic/Fermentation Microaerophilic Aerobe: Oxygen required but at lower levels than atmospheric. Aerobic Respiration only

Question 39

What is an Anaerobic Microorganism and what are the types?

Answer 39

Aerotolerant Anaerobe: Oxygen not required but grows better without it. Fermentation only. Obligate Anaerobe: Oxygen lethal/harmful. Fermentation or anaerobic respiration

Question 40

How do you reduce microbial growth?

Answer 40

Low Temp = Refrigeration Low pH = Pickling Low Water = Drying Low Oxygen = Vacuum Sealing