Bacteria

Genetic Properties of Bacteria

• Bacterial chromosome: where genes of bacteria are found
• Usually a single type of chromosome
• May have more than one copy of that chromosome
• Number of copies depends on the bacterial species and on growth conditions
• Typically 1-4 identical chromosomes
• Nucleoid: region where tightly packed bacterial chromosome found

Bacterial Chromosomes

• Molecules of double-stranded DNA
• Usually circular
• Tend to be shorter
• Contains a few thousand unique genes
• Mostly structural genes
• Single origin of replication

Plasmids

• Plasmids: small, circular pieces of DNA that exist independently of the bacterial chromosome
• Occur naturally in many strains of bacteria and in \n a few types of eukaryotic cells, such as yeast
• Own origin of replication that allows it to be replicated independently of the bacterial chromosome
• Not usually necessary for survival but can provide growth advantages
• Episome: plasmid that can integrate into bacterial chromosome

Five Types of Plasmids

1. Resistance plasmids (R factors): confer resistance against antibiotics and other types of toxins
2. Degradative plasmids: enable the bacterium to digest and utilize an unusual substance
3. Col-plasmids: encode colicines, which are proteins that kill other bacteria
4. Virulence plasmids: turn a bacterium into a pathogenic strain
5. Fertility plasmids (F factors): allow a bacteria to mate

Reproduction

• Some species like E. coli can divide every 20-30 minutes
• Single cell can form a bacterial colony in less than a day
• Reproduce by  binary fission - NOT mitosis
• Unless a mutation occurs, each daughter cell contains \n an identical copy of the mother cell’s genetic material
• Does not involve genetic contributions from two different parents
• Plasmids may replicate independently of the bacterial chromosome

Bacteria Structure

• A cytoplasmic membrane
  • surrounded by a peptidoglycan cell wall
  • may have an outer membrane
• A fluid cytoplasm containing
  • nuclear region (nulceoid)
  • ribosomes
• External structures such as pili, glycocalyx, and flagella
• 3 shapes of bacteria are coccus, bacillus, and spiral

The Bacterial Cell Wall

• Protection from osmotic lysis
• Provides shape to the bacteria
• In direct contact with the environment
• Pathogenesis
• Cell walls contain peptidoglycan cross-linked by polypeptides

Ribosomes, Inclusions, and Endospores

• Ribosomes: consist of RNA plus protein: sites of protein synthesis
• Inclusions: aggregates of various compounds that are normally involved in storing energy reserves or building blocks for the cell.
• Endospores are resistant to 
  • High temperatures (including boiling)
  • Most disinfectants, low energy radiation, drying
  • The endospore can survive thousands of years until some environmental stimulus triggers germination

Bacterial Flagella

• Usually found on bacilli and some spirals
• Composed of flagellin
• Involved in locomotion
• Allows bacteria to respond to specific stimuli
  • Chemotaxis
  • Magnetotaxis

Glycocalyx

• Functions include
  • Attachment to surfaces
  • Protection from desiccation
  • Nutrient trap
  • Protection from phagocytosis
  • Protection from certain toxins
  • Detergents