Bacterial Genetics 1

Question 1

Study of Bacterial Genetics

Answer 1

• study of hereditary and variation of inherited characteristics
• vast majority of bacteria are haploid
• so mutations are not recessive
• but horizontal gene transfer is possible between bacteria

Question 2

Streptomyces

Answer 2

• often used to produce antibiotic resistance
• they have a secondary metabolism which produces antibacterial chemicals
• this gives them a selective advantage as they can use those chemicals to destroy their competition

Question 3

Cyanobacteria

Answer 3

• evidence of their existence, 3.5bya
• major primary producer of the planetary ocean
• photoautotrophs
• can fix atmospheric nitrogen
• photosynthesise to release energy
• though to have played a major role in the conversion of the early reducing atmosphere to an oxygenic one

Question 4

Photoautotrophs

Answer 4

-produce organic compounds using CO2 as a carbon source sunlight for energy

Question 5

Bacteria and Domains

Answer 5

• bacteria make up one of two domains of prokaryotes
• prokaryotes are split into two domains, archaea (archaebacteria) and bacteria (eubacteria)
• all bacteria are prokaryotes but not all prokaryotes are bacteria, some are archaea

Question 6

Archaebacteria

Answer 6

-have eukaryotic features e.g. transcription, translation

Question 7

Prokaryotes

Answer 7

• arguably the most evolutionary diverse group of free living organisms
• but only a few prokaryotic organisms have ever been manipulate genetically
• much of what is known about prokaryotic genomes is based on extrapolation

Question 8

Hydrothermal Vents

Answer 8

• possible sites for the origin of life
• spew out H2S and FeS which can both be oxidised to release energy
• 400C

Question 9

Hydrothermal Vents and Bacteria

Answer 9

• chemoautotrophs
• bacteria at vents oxidise hydrogen sulphide and iron sulphide to release energy
• can be primary producers e.g. by hydrogen sulphide chemosynthesis

Question 10

Extremophiles

Answer 10

-many are archaea
-organisms live in extreme environments:
cold
acidic/alkaline/saline water
geyser

Question 11

Mesophiles

Answer 11

found in marshland, sewage, sea water and soil

Question 12

Methanogenic Archaea

Answer 12

found in animal digestive tract

Question 13

Are archaea pathogens?

Answer 13

-as of 2007 no clear examples of archaeal pathogens are known

Question 14

Wolbachia

Answer 14

• genus of inherited bacteria
• infects arthropod species including many insects
• able to alter reproductive abilities of host
  e. g. male killing, feminisation, parthenogenesis
• could be genetically manipulated and used to control pest populations

Question 15

Parthenogenesis

Answer 15

-killing one sex of a species over another

Question 16

Exploiting Secondary Metabolism

Answer 16

• exploit bacteria as producers of secondary metabolites as possible precursors for new drugs
• beginning to be able to predict the metabolism of organisms from the sequence of their genes
• using whole pathways to produce products rather than individual genes

Question 17

Texiobactin

Answer 17

• new antibiotic
• found from soil, produced by bacteria
• works well against gram positive bacteria
• difficult to isolate as bacteria were initially unable to survive in a lab environment and had to be domesticated

Question 18

Bioremediation

Answer 18

• minimise effectiveness of bacteria as weapons of mass destruction, to eradicate them or negate their pathogenicity
• using bacteria to digest radioactive waste

Question 19

MRSA

Answer 19

• methicillin/multiple resistant staphylococcus aureus

- resistant to B lactern antibiotics

Question 20

Bacteria That Cause Human Disease

Answer 20

• only a small fraction of bacteria that cause disease in humans
• bacterial infection can be prevented by killing bacteria with heat or vaccination
• if bacterial infection does occur doctors may treat with antibiotics
• but over and improper use of antibiotics leads to the development f strains that are antibiotic resistance e.g. Mycobacterium tuberculosis

Question 21

Methods for Studying Bacterial Genetics

Answer 21

• need visible phenotypes to study genetics but bacteria are only micrometres in length
  e. g. use antibiotic resistance

Question 22

Growing Bacteria

Answer 22

1) start with a suspension of bacterial cells
2) spread onto an agar plate
3) single cells are not visible to the naked eye
4) incubate for 1 to 2 days
5) colonies that are clones of each of the individual cells are now visible on the plate

Question 23

Streptomycin Resistance

Answer 23

• occurs at a frequency of a one in a million in E.coli

- occurs spontaneously

Question 24

Antibiotic Resistance and Mutation

Answer 24

-a single point mutation can lead to antibiotic resistance

Question 25

Antibiotic Resistance and Evolution

Answer 25

-acquisition of antibiotic resistance is often cited as a prime example of evolution

Question 26

What does a Darwinian Process require?

Answer 26

• self replication/inheritance, some number of the organism must be capable of producing copies of themselves and those copies must also be able to reproduce
• variation, a range of traits and a mechanism for introduction of new traits into the population
• selection, inherited traits must affect the ability of organisms to survive to reproduce

Question 27

Evolution

Definition

Answer 27

• a process in which a populations inherited traits become more common at the expense of others from generation to generation
• as differences in and between populations accumulate over time specitation can occur

Question 28

What do bacteria need to grow?

Answer 28

• E.coli and many other bacteria are easy to grow

- many bacteria are able to produce everything they need from a simple sugar, nitrogen source, salts and trace metals

Question 29

Prototroph

Definition

Answer 29

-strains of an organism that can proliferate on a minimal medium, wildtype

Question 30

Minimal Medium

Answer 30

-only contains a simple carbon source

Question 31

Auxotrophs

Definition

Answer 31

-mutant strains of an organism that can only proliferate when the medium is supplemented with some specific substance not required by the wildtype

Question 32

Selecting for Loss of Function Mutants - Isolating Auxotrophs

Answer 32

1) start with a population of bacteria
2) spread on to an agar plate
3) grow to produce colonies of each cell
4) press a velveteen surface on to the master plate, some of the cells from each colony will transfer to the velveteen producing a stamp of the master plate
5) press stamp on to a minimal medium plate
6) leave to grow
7) compare master and minimal medium plates, colonies that can grow on the master plate but not on the minimal medium are the auxotrophs

Question 33

Genetic Reversion

Answer 33

• a return to a prior state by a second mutation
• the mutation could be the exact opposite of the original mutation
• or a second, different mutation that reverses the effects of the first mutation
• genetic reversion allows auxotrophs to become prototrophs

Question 34

Lederberg & Tatum Experiment - Method

Answer 34

• started with two auxotrophic strains of bacteria, Strain A required biotin & methionine, Strain B required threonine & leucine & thiamine
• when strain A was plated on a minimal medium, no colonies grew
• when strain B was plated on a minimal medium, no colonies grew
• when strain A and strain B were mixed and plated on a minimal medium, colonies did grow

Question 35

Lederberg & Tatum Experiment - Conclusion

Answer 35

• when the strains were mixed, cells were produced that were able to grow on a minimal medium
• prototrophic cells were produced from auxotrophic cells
• the reversion frequency is 1 in a million so frequency of spontaneous occurrence of wildtype cells from the mutants would be 1 in 10^18
• in the experiment, wildtype colonies were obtained at a frequency of 1 in 10^6-10^7
• so the results must have been as a result of a sexual process in bacteria and not genetic reversion