Week 2: Bacterial Reproduction and Growth

Binary fission (simple division)

–form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size

1. Cell elongates and DNA is replicated

2. Cell wall and plasma membrane begin to divide

3. Transverse septum (wall, cross-wall) forms completely around divided DNA

(a) due to continued growth of cell wall and membrane

• (b) divides contents of cell and DNA
• molecules

4. Cells separate

•Lag phase: no change in number of cells, metabolically getting ready but not yet dividing

•Log (or exponential) phase:bacteria grow in steady state, no cell death

•Stationary phase: rate of reproduction = rate of death

•Death phase: cells dying in steady state

• Log phase bc antibacterial target biosynthesis of
• bacteria

1)Temperature

2)pH

3)Oxygen

4)Water 

5)Light

6)Nutrients

Optimum temp. - temp. at which maximum growth occurs

• 3 groups:
• 1. Thermophiles: 45°C - 110°C
• (e.g. hot springs, volcanoes in ocean, decomposers)

• 2. Mesophiles: 20°C - 45°C
• (e.g. environmental bacteria, pathogen)

• 3. Psychrophiles: 0°C  - 20°C
• (e.g. cold springs, lakes; polar regions; refrigerator)

C) mesophiles

- Optimum pH - pH at which maximum growth occurs

• 3 groups
• 1. Alkalinophiles: 8 to 12
• (e.g. Soil bacteria)

2. Neutrophiles: 5 to 8

• 3. Acidophiles: 0 to 5
•  (e.g. Helicobacter pylori - stomach ulcers)

C) neutrophiles

1.Obligate

2.Obligate anaerobic

3.Facultative

4.Microaerophile

5. Aerotolerant anaerobic

• 1. superoxide dismutase
• - obligate aerobes
• - facultative anaerobes (most)
• - aerotolerant anaerobes (most)

• 2. peroxidases
• - aerotolerant anaerobes (most)

• 3. catalase
• - obligate aerobes
• - facultative anaerobes (most)

All metabolically active bacteria require water

–Cells largely water

–Most nutrients, wastes soluble in water to cross cell membrane.

–Site of metabolic reactions (cytoplasm)

Very small group photosynthetic bacteria (cyanobacteria)  -  require UV light

- Nonphotosynthetic bacteria (eubacteria)  -  UV light is lethal (causes mutations)

Basic requirements for growth:

1. Carbon:building blocks of cell components

2. Nitrogen: production of proteins, nucleic acids

3. Hydrogen: occur in organic compounds

4. Oxygen:  involved in the production of energy

5: Minerals, trace elements: required in small amounts

- uses inorganic CO2 as a Carbon source

- making of own food by reducing CO2

- "self feeders"

• subgroups
• - photoautotrophs
• -chemoautotrophs

- uses organic compounds as Carbon source

- using ready-made organic molecules for food

- "other -feeders"

• subgroups:
• - photoheterotrophs
• - chemoheterotrophs

organic compound = energy source

• ex:
• - most bacteria
• - all protozoans
• - all fungi
• - all animals