Bacteria and Archea

  • Bacteria and archaea are microbes

  • Microbe: any organism that is too small to see with the naked eye

  • Microbes are not a taxonomic group- there are microbes in all three domains of life and outside the domains of life (viruses)

  • All bacteria and archaea are prokaryotes

  • Not all microbes are prokaryotes

  • The biomass of bacteria on earth is greater than the biomass of all animals combined

    Bacteria

  • Cell envelope

    • Made up of the plasma membrana and usually a cell wall

  • Cytoplasm

    • Contains proteins that digest food and convert energy

  • A genome composed of DNA

  • Ribosomes

  • May also have a cell capsule that prevents water loss

  • Genetic material can be found in two structures in the cytoplasm

  1. Chromosomes: contain circular DNA that codes for basic life processes

  2. Plasmids: contain circular DNA that encodes specific functions

  • Virulent: causing more severe disease

  • Bacteria reproduce asexually through binary fission (binary= two steps)

  • Binary Fission: the splitting of one cell into two identical cells

    1. Replication: chromosome and plasmid DNA are copied

    2. Cell elongates and divides into daughter cells

  • Daughter cells are genetically identical to each other and the original parent cell (unless random mutations occur)

  • So reproduction in bacteria does not increase genetic diversity

  • Bacteria have evolved ways to transfer genetic material laterally

  • Lateral transfer: the transfer of genetic material between individuals of the same generation (without reproduction)

  • Can happen in 3 ways:

  1. Conjugation: a bacterium transfers a copy of some of all of its DNA to another bacterium- genetic information the recipient may not have had

  2. Transformation: a bacterium can take up DNA- potentially including alleles it did not carry- from its surroundings (usually from bacteria that have died)

  3. Transduction: a virus containing pieces of bacterial DNA inadvertently picked up from its previous host infects a new bacterium- passing on genetic information the recipient may not have had

  • Gene transfer is not reproduction

  • Bacteria are sharing DNA with others in the same generation

Identifying Bacteria

  • Bacteria Shapes:

    • Cocci- spherical bacterial

    • Bacilli- rod shaped bacteria

    • Spirilla- spiral shaped bacteria

  • Many bacteria form colonies

  • Reproduce asexually

  • The number of cells doubles every generation

  • Generations can be as short as 1 hour

  • Bacterial colonies can be identified by their color and shape

  • Gran staining: a dye test used by microbiologists to identify an unknown bacterium and determine its susceptibility to antibiotics

  • Bacteria are usually transparent, so scientists apply a stain to view them under a microscope

  • This is why when you see photos of bacterial cells, they usually appear pink or purple

  • But this dye can also help us identify bacteria

  • Peptidoglycan: A protein that forms a protective layer on the outside of a bacterial cell wall and stains purple during gram staining. The peptidoglycan layer is thicker and unprotected in gram positive bacteria, and thinner and covered by a membrane in gram negative bacteria

  • Gram positive stains purple and negative stains pink

  • Gram staining can also tell us whether a bacterium can be treated with antibiotics

  • Many antibiotics work by damaging the bacterium’s protective layer of peptidoglycan

  • Gram positive are more susceptible to antibiotics while gram negative are less

  • We can also identify bacteria by looking at their genetic sequence, or doing other lab tests that test their chemistry and metabolism

  • Bacteria can digest almost everything

  • Scientists are now exploring ways to bioengineer bacteria