Bacterial Growth, Nutrition, and Metabolism

What are the 4 Stages of a Bacterial Growth Curve?

1. lag

2. exponential (log)

3. stationary

4. death

What Happens During the Lag Phase?

• bacteria is adjusting to new environment

• cell synthesizing new components

  • to replenish or adapt

• varies in length (could be short or absent)

What Happens During the Exponential (Log) Phase?

• constant growth rate due to each bacterial division doubling the number of bacteria

• population is most uniform

  • physically and chemically

What Happens During the Stationary Phase?

• total number of viable cells remain constant

  • cell division = death rate

• occurs due to limited resources (food, space, etc.) or toxin accumulation

• starvation responses occur

What Are Bacterial Starvation Responses?

• increased virulence

  • MOST pathogenic during this time

• morphological changes

• production of starvation proteins

• long-term survival

What Happens During the Death Phase?

• decline in apparently viable cells

• some possiblities:

  • cell death

  • apoptosis of some to feed others

  • viable but not culturable (hibernation)

What are the Temperature and pH Requirements for Pathogenic Bacteria?

• optimal pH = 7.2 (physiological pH)

• optimal temp is around the average human temp

  • these bacteria are called mesophiles

What are Siderophores?

• released from bacteria to capture iron from circulation

• our bodies use transferrin to capture free iron

• competetion b/w siderophores and transferrin to capture the available iron

• bacteria with effective siderophores are more pathogenic

What is an Obligate Aerobe?

bacteria that need oxygen

What is a Facultative Anaerobe?

bacteria that prefer oxygen

What is an Aerotolerant Anaerobe?

bacteria that have no preference for or against oxygen

What is an Obligate Anaerobe?

oxygen is toxic to these bacteria

What is a Microaerophile?

bacteria that can ONLY tolerate a narrow oxygen level range

What Toxic Byproducts are Produced by Aerobes?

• superoxide radical (O₂^- •)

• hydrogen peroxide (H₂O₂)

How Do Aerobic Bacteria Protect Themselves from Toxic Oxygen Byproducts?

• superoxide dismutase (SOD)

  • 2O₂^- • + 2H⁺ → H₂O₂ + O₂

• Catalase

  • 2H₂O₂ → 2H₂O + O₂

What Protective Enzymes do Obligate Aerobes Have?

• superoxide dismutase (SOD)

• catalase

What Protective Enzymes do Facultative Anaerobes Have?

• superoxide dismutase (SOD)

• catalase

What Protective Enzymes do Aerotolerant Anaerobes Have?

ONLY superoxide dismutase (SOD)

What Protective Enzymes do Obligate Anaerobes Have?

none

What Protective Enzymes do Microaerophiles Have?

• superoxide dismutase (SOD)

• low levels of catalase

What are the 3 Common Ways Bacteria Catabolize Glucose to Pyruvate?

1. glycolysis (done by aerobes and anaerobes)

2. pentose phosphate pathway

3. Entner-Doudoroff pathway (only a few bacteria do this)

What are the 2 Parts of Aerobic Respiration and How Much ATP is Made?

• glycolysis + oxidative phosphorylation

• 32 ATP is made

What are the 2 Parts of Anaerobic Respiration and How Much ATP is Made?

• glycolysis + fermentation

• less than 32 ATP 

  • fermentation ALWAYS makes less ATP than oxidative phosphorylation

How Does Oxygen Use and ATP Production Affect Growth/Replication?

aerobic respiration produces more ATP ∴ the bacteria has more energy to grow/replicate

How Does DNA Replication Differ Between Prokaryotes and Eukaryotes?

prokaryotic DNA polymerases are much faster but have a lower fidelity

How Does Protein Synthesis Differ Between Prokaryotes and Eukaryotes?

in prokaryotes, ribosomes translate mRNA while it is being translated

• this coupled process makes it much faster

What are the Steps of Cell Wall Synthesis?

1. NAM is synthesized in the cytoplasm while attached to UDP

2. NAM binds to bactoprenol in the cell membrane

   • bactoprenol shuttles NAM and NAG outside the plasma membrane

3. in the cell membrane, NAM and NAG are attached to each other

4. outside of the cell membrane, NAM and NAG are attached to the growing peptidoglycan chain

5. bactoprenol moves back to the inner membrane

   • resets the process

What are the Functions of Autolysin?

1. cleaves peptidoglycan to allow cell division

2. removes old cell wall fragments for basic maintanence