Bacteria: Life Cycle

1. Bacteria: Life Cycle SBI3UI: Unit 3 – Lesson 2

2. A. Growth Rate • Because of the way that bacteria divide, they tend to grow exponentially! One cell becomes 2, which becomes 4, which becomes 8, which becomes 16, . . . • Under favourable conditions, some bacteria can divide every 20 minutes! At this rate, how many bacteria would you find after 12 hours if the initial colony contained 1 member?

3. Bacterial Growth Curve • Lag Phase: adjusting to the environment; slower growth • Exponential Growth Phase: very rapid growth; reproduction rate > death rate • Stationary Phase: reproduction rate = death rate • Death Phase: reproduction rate < death rate

4. I. Binary Fission • The chromosome duplicates and attaches to the cell membrane • The cell elongates, causing the 2 identical chromosomes to pull apart (new plasma membrane and cell wall are forming) • Septum forms • Cell is divided into two identical cells

5. II. Conjugation • This is the process of exchanging genetic material (DNA) between bacterial cells. • Plasmids are foreign pieces of circular DNA carried by some bacterial cells. • The genetic information transferred via plasmids is often beneficial to the recipient. • Benefits may include antibiotic resistance, xenobiotic(foreign pollutant) tolerance or the ability to use new metabolites.

6. “Male” (F+) and “female” (F-) cells meet • Pilus forms from F+ to F- and the double-stranded circular plasmid “unzips” • One complementary strand of the plasmid’s DNA enters the F- cell • Plasmid re-circularizes in F- cell • Complementary strands of DNA are synthesized in each cell • Both cells can now reproduce by binary fission and transfer plasmids to other cells

7. Conjugation (cont’d)

8. Conjugation (cont’d)

9. Conjugation (cont’d)

10. C. Endospore Formation (Sporulation) • Some bacteria can form an endospore when conditions are not favourable • Endospores are dormant structures that can resist drying, heating, freezing, radiation, etc. • They become vegetative again when favourable conditions resume!

11. Endospore Structure Spore Coat Exosporium Ribosomes DNA Core Wall Cortex

13. Anthrax • Anthrax is an acute disease caused by the bacteria Bacillus anthracis. Most forms of the disease are lethal, and it affects both humans and other animals. There are effective vaccines against anthrax, and some forms of the disease respond well to antibiotic treatment. • Like many other members of the genus Bacillus, Bacillus anthracis can form dormant spores that are able to survive for decades or even centuries.Such spores can be found on all continents, even Antarctica.When spores are inhaled, ingested, or come into contact with a skin lesion on a host they may reactivate and multiply.

14. Tetanus • Tetanus, also called lockjaw, is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. • The primary symptoms are caused by a neurotoxin produced by the obligate anaerobic bacterium Clostridium tetani.

15. Botulism • Botulism is a rare but serious paralytic illness caused by botulinum toxin, which is produced by the bacterium Clostridium botulinum under anaerobic conditions. • Leads to paralysis that typically starts with the muscles of the face and then spreads towards the limbs. • In severe forms, it leads to paralysis of the breathing muscles and causes respiratory failure. • Can be prevented by killing the spores by cooking at 121 °C (250 °F) for 3 minutes or providing conditions that prevent the spores from growing. Additional precautions for infants include not feeding them honey.

16. Gas Gangrene • Gas gangrene is a deadly form of gangrene usually caused by Clostridium perfringens bacteria. It is a medical emergency. • In wartime, in particular, the unhygienic conditions and frequent gross injuries meant that gangrenous infection of soil-borne bacteria was particularly prevalent. Indeed, mankind has long suffered the ill-effects of gangrenous infections throughout history!

17. The End! HW: Read p. 424-426, p. 428, and p. 429 in your text. Add/integrate any new information into your notes.