C2.3 - Bacterial Growth

Culturing Bacteria in Lab

• Bacteria studied on media called agar
• Nutrient agar has all nutrients required for growth of most bacteria
• Bacterial colonies form on agar
• Contain millions of individual bacteria
• Characteristic shapes depending on species

Conditions Inhibiting Bacterial Growth

Temperature

• Most bacteria live best at 28-36 °C
• Human take steps to limit bacterial growth by:
  • boiling
  • refrigerating
  • freezing
  • pasteurizing
• Animals raise their body temp. to slow bacterial infections
• permafrost: permanently frozen, helps preserve (no bacteria decomp.)
• pasteurization: boil, then cool down to slow bacterial growth

(Lack of) Moisture

• Bacteria must have wet/moist environments to grow
• Lack of moisture = bad for bacteria
• i.e. dehydrated food

Mummification

King Tut Before

King Tut After 3,300 Years

• Body got dark from oxidization
• natron: natural salt in Egpyt used to dehydrate Mummy
• mummia: oil used to preserve mummies
• Moist organs removed
• Mummies protected from tomb robbing
• Key Point: Body was preserved through dehydration and chemical processes

Radiation

• Uses electromagnetic radiation (X-Rays, UV light) and gamma rays
• Interferes with DNA replication and either slows or stops bacterial reproduction
• e.g. irradiated food and water

Chemicals

• Extreme pHs and salts kill bacteria or cause them to go dormant
• e.g. canned foods, salted meats, household cleaners and antibiotic compounds

Bog People

Tollund Man Before

Tollund Man After 2,300 Years

• Bog preserves human
• Tannic acid turned human skin into leather

Bacterial Reproduction

• Bacteria reproduce at exponential rates
• Population doubling by binary fission can occur every 20-60 mins.
• binary fission: seperation of the body into two new bodies
• Bacteria reproduce asexually
• Bacteria can exchange genetic information through conjugation or transformation

Diagram of binary fission:

Bacterial Conjugation

• bacterial conjugation: asexual process where bacterial DNA is transferred to another bacterium
• DNA loop called a plasmid transferred
• Plasmid donated to other cell via tube called a pilus
• Plasmid can exist either on its own in cell cytoplasm or integrated into larger, circular chromosome
• Genetic mutations and DNA transferring causes strains like multidrug resistant TB

Other Methods of Bacterial Surival

• transformation: bacteria take up pieces of DNA from environ.
  • sources: nearby dead bacteria
• transduction: bacteria receive new genetic material from bacteriophage injection
• endospore: dormant stage of bacteria
  • when resources too limited
  • thick internal wall circles DNA and small amount of cytoplasm
  • outer cell disintegrates
  • can absorb water and grow again when environ. more favourable

How Do Bacteria Communicate?

• quorum sensing: the use of chemical signals by bacteria to communicate with each other
• Allows bacteria to act in unison, like a multicellular organism
• Quorum sensing controls:
  • virulence: degree to which bacteria can infect its host
  • biofilm formation
  • DNA exchange
• Significant for medicine, leading to develop new antibiotics that target this communication system