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© 2012 Pearson Education, Inc. I. Bacterial Cell Division. 5.1 Cell Growth and Binary Fission 5.2 Fts Proteins and Cell Division 5.3 MreB and Determinants of Cell Morphology 5.4 Peptidoglycan Synthesis and Cell Division. © 2012 Pearson Education, Inc. 5.1 Cell Growth and Binary Fission.

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i bacterial cell division

© 2012 Pearson Education, Inc.

I. Bacterial Cell Division
  • 5.1 Cell Growth and Binary Fission
  • 5.2 Fts Proteins and Cell Division
  • 5.3 MreB and Determinants of Cell Morphology
  • 5.4 Peptidoglycan Synthesis and Cell Division
5 1 cell growth and binary fission

© 2012 Pearson Education, Inc.

5.1 Cell Growth and Binary Fission
  • Binary fission: cell division following enlargement of a cell to twice its minimum size (Figure 5.1)
  • Generation time: time required for microbial cells to double in number
  • During cell division, each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell
figure 5 1

Figure 5.1

Cellelongation

One generation

Septumformation

Septum

Completionof septum;formation ofwalls; cellseparation

© 2012 Pearson Education, Inc.

5 2 fts proteins and cell division

© 2012 Pearson Education, Inc.

5.2 Fts Proteins and Cell Division
  • Fts (filamentous temperature-sensitive) Proteins (Figure 5.2)
    • Essential for cell division in all prokaryotes
    • Interact to form the divisome (cell division apparatus)
      • FtsZ: forms ring around center of cell; related to tubulin
      • ZipA: anchor that connects FtsZ ring to cytoplasmic membrane
      • FtsA: helps connect FtsZ ring to membrane and also recruits other divisome proteins
        • Related to actin
5 2 fts proteins and cell division1

© 2012 Pearson Education, Inc.

5.2Fts Proteins and Cell Division
  • DNA replicates before the FtsZ ring forms (Figure 5.3)
  • Location of FtsZ ring is facilitated by Min proteins
    • MinC, MinD, MinE
  • FtsK protein mediates separation of chromosomes to daughter cells
figure 5 2

Figure 5.2

Outer membrane

Peptidoglycan

Cytoplasmic membrane

Divisomecomplex

FtsZ ring

Cytoplasmic membrane

© 2012 Pearson Education, Inc.

5 3 mreb and determinants of cell morphology

© 2012 Pearson Education, Inc.

5.3 MreB and Determinants of Cell Morphology
  • Prokaryotes contain a cell cytoskeleton that is dynamic and multifaceted
  • MreB: major shape-determining factor in prokaryotes
    • Forms simple cytoskeleton in Bacteria and probably Archaea
    • Forms spiral-shaped bands around the inside of the cell, underneath the cytoplasmic membrane (Figure 5.4a and b)
    • Not found in coccus-shaped bacteria
5 3 mreb and determinants of cell morphology1

© 2012 Pearson Education, Inc.

5.3 MreB and Determinants of Cell Morphology
  • MreB (cont’d)
    • Localizes synthesis of new peptidoglycan and other cell wall components to specific locations along the cylinder of a rod-shaped cell during growth
figure 5 4a

Figure 5.4a

FtsZ

Cell wall

Cytoplasmicmembrane

MreB

Sites of cellwall synthesis

© 2012 Pearson Education, Inc.

figure 5 4b

Figure 5.4b

© 2012 Pearson Education, Inc.

5 3 mreb and determinants of cell morphology2

© 2012 Pearson Education, Inc.

5.3 MreB and Determinants of Cell Morphology
  • Most archaeal genomes contain FtsZ and MreB-like proteins, thus cell morphology is similar to that seen in Bacteria
5 4 peptidoglycan synthesis and cell division

© 2012 Pearson Education, Inc.

5.4 Peptidoglycan Synthesis and Cell Division
  • Production of new cell wall material is a major feature of cell division
    • In cocci, cell walls grow in opposite directions outward from the FtsZ ring
    • In rod-shaped cells, growth occurs at several points along length of the cell
5 4 peptidoglycan synthesis and cell division1

© 2012 Pearson Education, Inc.

5.4 Peptidoglycan Synthesis and Cell Division
  • Preexisting peptidoglycan needs to be severed to allow newly synthesized peptidoglycan to form
    • Beginning at the FtsZ ring, small openings in the wall are created by autolysins
    • New cell wall material is added across the openings
    • Wall band: junction between new and old peptidoglycan
figure 5 5

Figure 5.5

FtsZ ring

Growth zone

Wall bands

Septum

© 2012 Pearson Education, Inc.

figure 5 4a1

Figure 5.4a

FtsZ

Cell wall

Cytoplasmicmembrane

MreB

Sites of cellwall synthesis

© 2012 Pearson Education, Inc.

5 4 peptidoglycan synthesis and cell division2

© 2012 Pearson Education, Inc.

5.4 Peptidoglycan Synthesis and Cell Division
  • Bactoprenol: carrier molecule that plays major role in insertion of peptidoglycan precursors
    • C55 alcohol (Figure 5.6)
    • Bonds to N-acetylglucosamine/N-acetylmuramic acid/pentapeptide peptidoglycan precursor
5 4 peptidoglycan synthesis and cell division3

© 2012 Pearson Education, Inc.

5.4 Peptidoglycan Synthesis and Cell Division
  • Glycolases: enzymes that interact with bactoprenol (Figure 5.7a)
    • Insert cell wall precursors into growing points of cell wall
    • Catalyze glycosidic bond formation
figure 5 7a

Figure 5.7a

Peptidoglycan

Growing pointof cell wall

Transglycosylaseactivity

Autolysinactivity

Cytoplasmicmembrane

Out

In

Pentapeptide

Bactoprenol

© 2012 Pearson Education, Inc.

5 4 peptidoglycan synthesis and cell division4

© 2012 Pearson Education, Inc.

5.4 Peptidoglycan Synthesis and Cell Division
  • Transpeptidation: final step in cell wall synthesis (Figure 5.7b)
    • Forms the peptide cross-links between muramic acid residues in adjacent glycan chains
    • Inhibited by the antibiotic penicillin
figure 5 7b

Figure 5.7b

Transpeptidation

© 2012 Pearson Education, Inc.

ii population growth

© 2012 Pearson Education, Inc.

II. Population Growth
  • 5.5 The Concept of Exponential Growth
  • 5.6 The Mathematics of Exponential Growth
  • 5.7 The Microbial Growth Cycle
5 5 the concept of exponential growth

© 2012 Pearson Education, Inc.

5.5 The Concept of Exponential Growth
  • Most bacteria have shorter generation times than eukaryotic microbes
  • Generation time is dependent on growth medium and incubation conditions
5 5 the concept of exponential growth1

© 2012 Pearson Education, Inc.

5.5 The Concept of Exponential Growth
  • Exponential growth: growth of a microbial population in which cell numbers double within a specific time interval
  • During exponential growth, the increase in cell number is initially slow but increases at a faster rate (Figure 5.8)
5 7 the microbial growth cycle

© 2012 Pearson Education, Inc.

5.7 The Microbial Growth Cycle
  • Batch culture: a closed-system microbial culture of fixed volume
  • Typical growth curve for population of cells grown in a closed system is characterized by four phases (Figure 5.10):
    • Lag phase
    • Exponential phase
    • Stationary phase
    • Death phase

Animation: Bacterial Growth Curve

figure 5 10

Growth phases

Exponential

Stationary

Death

Lag

Figure 5.10

1.0

10

0.75

Optical density (OD)

9

Turbidity(optical density)

Log10 viableorganisms/ml

0.50

Viable count

8

0.25

7

6

0.1

Time

© 2012 Pearson Education, Inc.

5 7 the microbial growth cycle1

© 2012 Pearson Education, Inc.

5.7 The Microbial Growth Cycle
  • Lag phase
    • Interval between when a culture is inoculated and when growth begins
  • Exponential phase
    • Cells in this phase are typically in the healthiest state
  • Stationary phase
    • Growth rate of population is zero
    • Either an essential nutrient is used up or waste product of the organism accumulates in the medium
5 7 the microbial growth cycle2

© 2012 Pearson Education, Inc.

5.7 The Microbial Growth Cycle
  • Death Phase
    • If incubation continues after cells reach stationary phase, the cells will eventually die
iv temperature and microbial growth

© 2012 Pearson Education, Inc.

IV. Temperature and Microbial Growth
  • 5.12 Effect of Temperature on Growth
  • 5.13 Microbial Life in the Cold
  • 5.14 Microbial Life at High Temperatures
figure 5 18

Enzymatic reactions occurringat maximal possible rate

Optimum

Enzymatic reactions occurringat increasingly rapid rates

Figure 5.18

Growth rate

Minimum

Maximum

Temperature

Membrane gelling; transportprocesses so slow that growthcannot occur

Protein denaturation; collapseof the cytoplasmic membrane;thermal lysis

© 2012 Pearson Education, Inc.

5 12 effect of temperature on growth

© 2012 Pearson Education, Inc.

5.12 Effect of Temperature on Growth
  • Microorganisms can be classified into groups by their growth temperature optima (Figure 5.19)
    • Psychrophile: low temperature
    • Mesophile: midrange temperature
    • Thermophile: high temperature
    • Hyperthermophile: very high temperature
figure 5 19

Thermophile

Example:Geobacillusstearothermophilus

Hyperthermophile

Hyperthermophile

Figure 5.19

Example:Pyrolobus fumarii

Example:Thermococcus celer

Mesophile

Example:Escherichia coli

60°

106°

88°

39°

Growth rate

Psychrophile

Example:Polaromonas vacuolata

20

30

40

50

60

70

80

90

100

110

120

0

10

Temperature (°C)

© 2012 Pearson Education, Inc.

5 12 effect of temperature on growth1

© 2012 Pearson Education, Inc.

5.12 Effect of Temperature on Growth
  • Mesophiles: organismsthat have midrange temperature optima; found in
    • Warm-blooded animals
    • Terrestrial and aquatic environments
    • Temperate and tropical latitudes
5 13 microbial life in the cold

© 2012 Pearson Education, Inc.

5.13 Microbial Life in the Cold
  • Extremophiles
    • Organisms that grow under very hot or very cold conditions
  • Psychrophiles
    • Organisms with cold temperature optima
    • Inhabit permanently cold environments (Figure 5.20)
  • Psychrotolerant
    • Organisms that can grow at 0ºC but have optima of 20ºC to 40ºC
    • More widely distributed in nature than psychrophiles
5 13 microbial life in the cold1

© 2012 Pearson Education, Inc.

5.13 Microbial Life in the Cold
  • Molecular Adaptations to Psychrophily
    • Production of enzymes that function optimally in the cold; features that may provide more flexibility
      • More -helices than -sheets
      • More polar and less hydrophobic amino acids
      • Fewer weak bonds
      • Decreased interactions between protein domains
5 13 microbial life in the cold2

© 2012 Pearson Education, Inc.

5.13 Microbial Life in the Cold
  • Molecular Adaptations to Psychrophily (cont’d)
    • Transport processes function optimally at low temperatures
      • Modified cytoplasmic membranes
        • High unsaturated fatty acid content
figure 5 22

Figure 5.22

© 2012 Pearson Education, Inc.

figure 5 23

Figure 5.23

© 2012 Pearson Education, Inc.

5 14 microbial life at high temperatures

© 2012 Pearson Education, Inc.

5.14 Microbial Life at High Temperatures
  • Studies of thermal habitats have revealed
    • Prokaryotes are able to grow at higher temperatures than eukaryotes
    • Organisms with the highest temperature optima are Archaea
    • Nonphototrophic organisms can grow at higher temperatures than phototrophic organisms
5 14 microbial life at high temperatures1

© 2012 Pearson Education, Inc.

5.14 Microbial Life at High Temperatures
  • Molecular Adaptations to Thermophily
    • Enzyme and proteins function optimally at high temperatures; features that provide thermal stability
      • Critical amino acid substitutions in a few locations provide more heat-tolerant folds
      • An increased number of ionic bonds between basic and acidic amino acids resist unfolding in the aqueous cytoplasm
      • Production of solutes (e.g., di-inositol phophate, diglycerol phosphate) help stabilize proteins
5 14 microbial life at high temperatures2

© 2012 Pearson Education, Inc.

5.14 Microbial Life at High Temperatures
  • Molecular Adaptations to Thermophily (cont’d)
    • Modifications in cytoplasmic membranes to ensure heat stability
      • Bacteria have lipids rich in saturated fatty acids
      • Archaea have lipid monolayer rather than bilayer
5 14 microbial life at high temperatures3

© 2012 Pearson Education, Inc.

5.14 Microbial Life at High Temperatures
  • Hyperthermophiles produce enzymes widely used in industrial microbiology
    • Example: Taq polymerase, used to automate the repetitive steps in the polymerase chain reaction (PCR) technique
v other environmental factors affecting growth

© 2012 Pearson Education, Inc.

V. Other Environmental Factors Affecting Growth
  • 5.15 Acidity and Alkalinity
  • 5.16 Osmotic Effects on Microbial Growth
  • 5.17 Oxygen and Microorganisms
  • 5.18 Toxic Forms of Oxygen
5 15 acidity and alkalinity

© 2012 Pearson Education, Inc.

5.15 Acidity and Alkalinity
  • The pH of an environment greatly affects microbial growth (Figure 5.24)
  • Some organisms have evolved to grow best at low or high pH, but most organisms grow best between pH 6 and 8 (neutrophiles)
figure 5 24

Moles per liter of:

pH Example

OH

H

1

1014

Volcanic soils, watersGastric fluidsLemon juice

101

1013

102

1012

Acid mine drainageVinegar

103

1011

Increasingacidity

RhubarbPeaches

Acidophiles

Figure 5.24

104

1010

Acid soilTomatoes

105

109

American cheeseCabbage

106

108

PeasCorn, salmon, shrimp

107

107

Neutrality

Pure water

106

108

Seawater

Very alkaline natural soil

105

109

104

1010

Alkaline lakes

Increasingalkalinity

Soap solutions

Alkaliphiles

103

Household ammoniaExtremely alkaline soda lakes

1011

102

1012

Lime (saturated solution)

101

1013

1

1014

© 2012 Pearson Education, Inc.

5 15 acidity and alkalinity1

© 2012 Pearson Education, Inc.

5.15 Acidity and Alkalinity
  • Acidophiles: organisms that grow best at low pH (<6)
    • Some are obligate acidophiles; membranes destroyed at neutral pH
    • Stability of cytoplasmic membrane critical
  • Alkaliphiles: organisms that grow best at high pH (>9)
    • Some have sodium motive force rather than proton motive force
5 15 acidity and alkalinity2

© 2012 Pearson Education, Inc.

5.15 Acidity and Alkalinity
  • The internal pH of a cell must stay relatively close to neutral even though the external pH is highly acidic or basic
    • Internal pH has been found to be as low as 4.6 and as high as 9.5 in extreme acido- and alkaliphiles, respectively
5 15 acidity and alkalinity3

© 2012 Pearson Education, Inc.

5.15 Acidity and Alkalinity
  • Microbial culture media typically contain buffers to maintain constant pH
5 16 osmotic effects on microbial growth

© 2012 Pearson Education, Inc.

5.16 Osmotic Effects on Microbial Growth
  • Typically, the cytoplasm has a higher solute concentration than the surrounding environment, thus the tendency is for water to move into the cell (positive water balance)
  • When a cell is in an environment with a higher external solute concentration, water will flow out unless the cell has a mechanism to prevent this
5 16 osmotic effects on microbial growth1

© 2012 Pearson Education, Inc.

5.16 Osmotic Effects on Microbial Growth
  • Halophiles: organisms that grow best at reduced water potential; have a specific requirement for NaCl (Figure 5.25)
  • Extreme halophiles: organisms that require high levels (15–30%) of NaCl for growth
  • Halotolerant: organisms that can tolerate some reduction in water activity of environment but generally grow best in the absence of the added solute
figure 5 25

Halophile

Halotolerant

Extremehalophile

Example:Aliivibrio fischeri

Example:Staphylococcusaureus

Example:Halobacteriumsalinarum

Figure 5.25

Growth rate

Nonhalophile

Example:Escherichia coli

20

10

15

5

0

NaCl (%)

© 2012 Pearson Education, Inc.

5 16 osmotic effects on microbial growth2

© 2012 Pearson Education, Inc.

5.16 Osmotic Effects on Microbial Growth
  • Osmophiles: organisms that live in environments high in sugar as solute
  • Xerophiles: organismsable to grow in very dry environments
5 16 osmotic effects on microbial growth3

© 2012 Pearson Education, Inc.

5.16 Osmotic Effects on Microbial Growth
  • Mechanisms for combating low water activity in surrounding environment involve increasing the internal solute concentration by
    • Pumping inorganic ions from environment into cell
    • Synthesis or concentration of organic solutes
      • compatible solutes: compounds used by cell to counteract low water activity in surrounding environment
5 17 oxygen and microorganisms

© 2012 Pearson Education, Inc.

5.17 Oxygen and Microorganisms
  • Aerobes: require oxygen to live
  • Anaerobes: do not require oxygen and may even be killed by exposure
  • Facultative organisms: can live with or without oxygen
  • Aerotolerant anaerobes: can tolerate oxygen and grow in its presence even though they cannot use it
  • Microaerophiles: can use oxygen only when it is present at levels reduced from that in air
5 17 oxygen and microorganisms1

© 2012 Pearson Education, Inc.

5.17 Oxygen and Microorganisms
  • Thioglycolate broth (Figure 5.26)
    • Complex medium that separates microbes based on oxygen requirements
    • Reacts with oxygen so oxygen can only penetrate the top of the tube
figure 5 26

Figure 5.26

Oxic zone

Anoxic zone

© 2012 Pearson Education, Inc.

5 17 oxygen and microorganisms2

© 2012 Pearson Education, Inc.

5.17 Oxygen and Microorganisms
  • Special techniques are needed to grow aerobic and anaerobic microorganisms (Figure 5.27)
  • Reducing agents: chemicals that may be added to culture media to reduce oxygen (e.g., thioglycolate)
figure 5 27

Figure 5.27

© 2012 Pearson Education, Inc.