Bacterial Genetics: Phenotypes and Genotypes Flashcards
Another definition of genetics - concerning phenotypes
- Field of biology on the relationship between genotypes + phenotypes
- An organism is basically the expression of its genes
- To study genetics, we need phenotypes
Bacterial Phenotypes - Use something
Encodes genes to make proteins to use:
- Sugar - Lactose /Maltose /Arabinose
- Electron acceptors (TEAs): Nitrate/DMSO/TMA
- Nutrients: Organic phosphates (tends to be tied to an organic molecule + needs protein to ‘cleave’ it off)
Bacterial Phenotypes - Make something
Encodes genes to make proteins to make the following that’s essential:
- Amino acids—proline, leucine, arginine, lysine +16 others
- Vitamins—thiamine, biotin, cobalamin, etc
- Metabolic product—lactate, acetate
Bacterial Phenotypes - Resistance to a chemical
Has genes to make them resistant to
- Antibiotics —ampicillin, chloramphenicol,
tetracycline, etc
- Other toxic chemicals like heavy metals —azide, mercury, et
Growth (e.g. as sole carbon source - if it uses lactose )
Colorimetric substrate (e.g. x-gal)
- Product of degradation (pH)
How to investigate that a bacteria can make something? **
- Growth in absence of thing such as an essential amino acids
resistant
- Growth in presence of thing such as a heavy metal
Prototrophy
Prototrophs do not have any nutritional requirements apart from a carbon source and some inorganic nutrients (and potentially a terminal electron acceptor)
- E.coli will grow on minimal media with nothing but glucose + inorganic salts
Auxotrophy
Require at least one organic molecule (besides a C source to grow)
- Usually an amino acid but can be something else
e.g. most lab strains of E. coli are thiamin auxotrophs (vitamin/coenzyme)
Shorthand for Phenotypes
- Abbreviations are short (usually 2-3 letters)
- First letter is always capital
- Never italicised
- Always an indicator (e.g. +/- for proto/auxotrophies
e.g. proline prototroph = Pro+
proline auxotroph = Pro-
Other superscript indicate others:
StrS = sensitivity to the antibiotic streptomycin
StrR = resistance to the antibiotic streptomycin
Detecting phenotypes using minimal media (MM)
- Only prototrophs can grow on MM
- Auxotrophs can only grow on MM if it is supplemented with the
required nutrient
e.g. screening for sugar auxotrophy - will only grow if sugar required
Minimal Media (MM)
Contains
- A carbon source (e.g. glucose, glycerol, succinate etc) for
energy and biosynthesis
- Inorganic salts—nitrogen, sulfur, iron, potassium,
phosphate, magnesium
Phenotype to genotype
If a bacteria is a certain phenotype e.g Pro+
- Must have certain gene products e.g. Pro A, B, and C
- Each is made by 3 separate genes - proA proB proC (if a mutation occurs in any of them, gene product isn’t made and is now Pro-)
Mutation in genotype affecting the phenotype
If a mutation occurs in any of the genes, gene product isn’t made and is now Pro-
- Won’t be able to detect which gene is defective or if more than one is
Genotype
Phenotype is result of genotype + may require more than 1
- If an organism contains a defective gene, we say that it
contains a mutation and that the strain is a mutant
Naming genes
Bacterial genes are (usually) named by the:
1. The phenotype they cause (or the cell component they
encode)—three letters
2. A specific locus
e.g. 3rd gene to cause Pro- phenotype is proC
e.g. rpsL -
Bacterial gene name rules for nomenclature
- Always italicised (can underlined in handwriting)
- Always have lowercase first letter (never capitalised)
- Never contain numbers
- If required: plus/minus is indicated by +/- superscript or
words: “mutant” v. “wild-type”
- If required: plus/minus is indicated by +/- superscript or
- “proC mutant” = “proC-“ can’t grow in absense in proline
- “Wild-type strain” = “proC+” can
Selective Media + Replica Plating
- A velvet surface on a replica block is put on a master plate of diff colonies (e.g containing leucine so Leu+/- grows)
- Replica block placed on a medium with (e.g. leucine) and a MM
- A colony missing in the medium lacking (leucine) compared to master plate is a “” requiring mutant
- Can then do further study on colony identified (can mark with felt tip)
