Microbial genetics for exam 3

MICROBIAL GENETICS & MICROBIAL INTERACTIONS

Last Lecture Sets for Examination 3

Monday, February 27, 2012

MICROBIAL GENETICS


TERMS IN MICROBIAL GENETICS

Genome: All of the genetic material in a cell

Genomics: The molecular study of genomes

Genotype: The genes of an organism

Phenotype: Expression of the genes


OVERVIEW


IMPORTANT ENZYMES


REGULATION OF GENE EXPRESSION


MUTATIONS

A change in the genetic material

Mutations may be neutral, beneficial, or harmful

Mutagen: Agent that causes mutations

Spontaneous mutations: Occur in the absence of a mutagen


TYPES OF MUTATIONS: MISSENSE


TYPES OF MUTATIONS: NONSENSE


TYPES OF MUTATIONS: FRAMESHIFT


REPAIRING MUTATIONS

Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone

Nucleotide excision repairs mutations.

UV radiation causes thymine dimers

Light-repair separates thymine dimers.


MUTATIONS IN THE LAB

FREQUENCY: Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes AND Mutagens increase to 10–5 or 10–3 per replicated gene

SELECTION:

Positive (direct) selection detects mutant cells because they grow or appear different

Negative (indirect) selection detects mutant cells because they do not grow.


CHARACTERIZING MUTATIONS


CHARACTERIZING MUTANTS

HYPOTHETICAL EXPERIMENT:

Using UV as mutagen you isolated colonies on your NA plates, to verify possible effects on phenotypes, you

TEST MEDIA ISOLATE 1 ISOLATE 2 ISOLATE 3

MINIMAL MEDIUM (MM) - - -MM + Penicillin + - -

MM + Erythromycin - - +MM + Rifampicin - + +

MM + glycine + - -MM + serine - - -

MM + methionine - + -




MINIMAL MEDIUM (MM) - - -MMG + Penicillin + - -

MMG + Erythromycin - - +MMG + Rifampicin - + +





Do you believe that they are all mutants? Justify.









Which isolate(s) has mutations that resulted to antibiotic resistance? Justify.










Which isolate(s) has mutations on the inability to produce an amino acid? Justify.










Which isolate(s) has mutations on the inability to produce an amino acid? Justify.

How will you name your isolate (E. coli) as a new strain?







MUTAGENICITY TEST: AMES TEST



SINCE IT’S V-DAY....


LET’S TALK ABOUT SEX!!!




Interested?




Interested?




Interested?

MICROBIAL GENETICS



GENE TRANSFERS

ENDPOINT: RECOMBINATION

Vertical gene transfer: Occurs during reproduction between generations of cells

Horizontal gene transfer: The transfer of genes between cells of the same generation

CONJUGATION, TRANSFORMATION, TRANSDUCTION


CONJUGATION


CONJUGATION


TRANSFORMATION


TRANSDUCTION


EXTRACHROMOSOMAL INHERITANCE: PLASMIDS

Conjugative plasmid: Carries genes for sex pili and transfer of the plasmid

Dissimilation plasmids: Encode enzymes for catabolism of unusual compounds

R factors: Encode antibiotic resistance


SOME METABOLIC ACTIVITIES DETERMINED BY PLASMIDS

ORGANISM ACTIVITY

Pseudomonas spp degradation of camphor, toluene, octane, salicyclic acid

Bacillus stearothermophilus alpha amylase

Alcaligenes eutrophus utilization of hydrogen as oxidizable energy source

E. coli sucrose uptake and and metabolism, citrate uptake

Klebsiella spp nitrogen fixation

Streptococcus (group N) lactose utilization, galactose phosphotransferase system, citrate metabolism

Rhodospirillum rubrum synthesis of photosynthetic pigment

Flavobacterium spp nylon degradation


EXTRACHROMOSOMAL INHERITANCE: TRANSPOSONS

Segments of DNA that can move from one region of DNA to another

Contain insertion sequences for cutting and resealing DNA (transposase)

Complex transposons carry other genes


Technology

Microbial genetics for exam 3