Bacterial Culture

Bacteria Articles:
Bacteria Culture:
  • Surprisingly, many, perhaps even most, of the bacteria on Earth cannot be grown in the laboratory today.
  • Bacteria need a set of specific nutrients, the correct amount of oxygen, and a proper temperature to grow. The common gut bacterium Escherichia coli (E. coli) grows easily on partially digested extracts made from yeast and animal products, at 37 degrees in a normal atmosphere. These simple growth conditions have made E. coli a favorite lab organism, which is used as a model for other bacteria.
Basic of Bacteria Culture
  • Bacteria are generally grown in either of 2 ways: on solid media as individual colonies, or in liquid culture.
  • The nutrient broth for liquid culture allows rapid growth up to a maximum density. Liquid culture is easy and cheap.
  • Solid media use the same nutrient broth as liquid culture, solidifying it with agar. Agar a polysaccharides derived from seaweed that most bacteria can’t digest.
  • The purpose of growth on solid media is to isolate individual bacterial cells, then grow each cell up into a colony. This is the standard way to create a pure culture of bacteria. All cells of a colony are closely related to the original cell that started the colony, with only a small amount of genetic variation possible.
  • Solid media are also used to count the number of bacteria that were in a culture tube.
Bacteria Mutant
  • Mutants in bacteria are mostly biochemical in nature, because we can’t generally see the cells.
  • The most important mutants are auxotrophs. An auxotroph needs some nutrient that the wild type strain (prototroph) can make for itself. For example, a trp- auxotroph can’t make its own tryptophan (an amino acid). To grow trp- bacteria, you need to add tryptophan to the growth medium. Prototroph's are trp+; they don’t need any tryptophan supplied since they make their own.
  • Chemoauxotrophs are mutants that can’t use some nutrient (usually a sugar) that prototrophs can use as food. For example, lac- mutants can’t grow on lactose (milk sugar), but lac+ prototrophs can grow on lactose.
  • Resistance mutants confer resistance to some environmental toxin: drugs, heavy metals, bacteriophage, etc. For instance, AmpR causes bacteria to be resistant to ampicillin, a common antibiotic related to penicillin.
  • Auxotrophs and chemoauxotrophs are usually recessive; drug resistance mutants are usually dominant.


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