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
  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
  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