Lesson 1 - Microbial culture media Flashcards
(15 cards)
Components of media (7)
- Nutrients: proteins/peptides/amino-acids.
- Energy: carbohydrates.
- Essential metals and minerals: calcium, magnesium, iron, trace metals: phosphates, sulphates etc.
- Buffering agents: phosphates, acetates etc.
- Indicators for pH change: phenol red, bromo-cresol purple etc.
- Selective agents: chemicals, antimicrobial agents.
- Gelling agent: usually agar.
Broth vs agar
Broth:
- Liquid
- Planktonic (free-floating) phase of microbial growth
- Used to reach specific growth phase
Agar
- Solid
- Isolated colonies or large biofilm phase of growth
- Further studies or long-term storage
Rich vs Minimal media
Rich contains diverse range of nutrients
- used to feed microbes
Minimal: water, carbon source, salts
- Used to study metabolism
Chemically defined vs complex media
Chemically defined (synthetic): known composition and quantity of nutrients
- metabolic studies/physiological
- for organisms that require specific nutrients for growth
- Can be rich or minimal
Complex: undefined assortment and quantity of nutrients
- extracts and enzymatic digests of organisms (peptones)
- everyday use
- Rich (usually)
Selective media
Allow the growth of a specified microbe because they contain ingredients that inhibit the growth of undesired microbe
Enriched media
Provide the extra nutrients to help difficult-to-grow organisms grow under laboratory conditions.
Differential Media
Contain ingredients that distinguish between different microbes and can indicate the presence of a certain microbe. Types of Microbial Culture Media
Our Media in lab and what they are
Luria Broth Bacterial media:
- Yeast, tryptone (N source), NaCl
YPD yeast media
- Yeast, peptone, dextrose
Rich + complex, not selective, enriched or differential
Controls
Experimental conditions meant to eliminate potential error sources (temp, gene activation)
Selectivity methods
Carbon Source Selection: This is like adding something specific (e.g., a sugar) that only the desired organisms can utilize, promoting their growth while others can’t use it.
Selective Inhibition: This involves adding substances (e.g., dyes, antibiotics, salts, inhibitors) that
target metabolism or enzyme systems to inhibit certain unwanted microorganisms.
Selectable Marker
Gene introduced into a cell that confers a trait suitable for artificial selection.
- Bacterial selectable markers are often antibiotic resistance genes
ex:
- Beta-lactamase which confers ampicillin resistance to bacterial hosts.
- Neo gene from Tn5, which confers resistance to kanamycin in bacteria and geneticin in eukaryotic cells
Multiple selective pressures example
The bacteria are transformed with a plasmid that contains:
1. An antibiotic resistance gene
2. The RFP gene, which makes the bacteria express a red fluorescent protein under certain conditions (like exposure to arabinose).
So -»>
Only bacteria that took up the plasmid survive (because of the antibiotic resistance gene).
Only bacteria that can express the RFP gene fluoresce red (because of arabinose-dependent expression).
Auxotrophy vs prototrophy
Auxotrophy: The inability of an organism to synthesize a particular organic compound required for its growth.
Prototrophy: is characterized by the ability to synthesize all the compounds needed for growth
Auxotrophs vs prototrophs
Auxotrophs are organisms that lose the ability to produce specific organic substances needed for their survival. Auxotrophs = mutant organisms
Prototrophs are organisms that are capable of producing all organic substances essential for their growth from inorganic compounds. Prototrophs = wild type organisms
Auxotrophic Marker
Gene that encodes a key enzyme for the production of an essential monomer used in biosynthesis
