Bacterial Genetics: Phenotypes and Genotypes

Question 1

Another definition of genetics - concerning phenotypes

Answer 1

• Field of biology on the relationship between genotypes + phenotypes
• An organism is basically the expression of its genes
• To study genetics, we need phenotypes

Question 2

Bacterial Phenotypes - Use something

Answer 2

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)

Question 3

Bacterial Phenotypes - Make something

Answer 3

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

Question 4

Bacterial Phenotypes - Resistance to a chemical

Answer 4

Has genes to make them resistant to
- Antibiotics —ampicillin, chloramphenicol,
tetracycline, etc
- Other toxic chemicals like heavy metals —azide, mercury, et

Answer 5

Growth (e.g. as sole carbon source - if it uses lactose )
Colorimetric substrate (e.g. x-gal)
- Product of degradation (pH)

Question 6

How to investigate that a bacteria can make something? **

Answer 6

• Growth in absence of thing such as an essential amino acids

Question 7

resistant

Answer 7

• Growth in presence of thing such as a heavy metal

Question 8

Prototrophy

Answer 8

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

Question 9

Auxotrophy

Answer 9

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)

Question 10

Shorthand for Phenotypes

Answer 10

• 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

Question 11

Detecting phenotypes using minimal media (MM)

Answer 11

• 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

Question 12

Minimal Media (MM)

Answer 12

Contains
- A carbon source (e.g. glucose, glycerol, succinate etc) for
energy and biosynthesis
- Inorganic salts—nitrogen, sulfur, iron, potassium,
phosphate, magnesium

Question 13

Phenotype to genotype

Answer 13

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-)

Question 14

Mutation in genotype affecting the phenotype

Answer 14

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

Question 15

Genotype

Answer 15

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

Question 16

Naming genes

Answer 16

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 -

Question 17

Bacterial gene name rules for nomenclature

Answer 17

• 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”
• “proC mutant” = “proC-“ can’t grow in absense in proline
• “Wild-type strain” = “proC+” can

Question 18

Selective Media + Replica Plating

Answer 18

• 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)