5. Microbial Taxonomy

Question 1

Define a type of strain and detail its purpose in microbiology

Answer 1

Acidithiobacillus ferrooxidans - a major participant in consortia of microorganisms used for the industrial recovery of copper (bio-leaching or bio-mining)

Question 2

How does the melting temperature determine nucleic acid base composition of DNA

Answer 2

As the DNA melts, the percentage of adenine and thymine in the melted sequences decreases. Linearly with temperature. The average composition of sequences which melt in a given part of the melting curve is proportional to the base ratio of the DNA.

Question 3

Describe the role horizontal gene transfer plays in evolution of prokaryotes with examples

Answer 3

• Horizontal gene transfer is the primary mechanism for the spread of antibiotic resistance in bacteria and plays an important role in the evolution of bacteria that can degrade novel compounds such as human created pesticides and in the evolution, maintenance and transmission of virulence

Question 4

Describe the difference between a phenetic and a phylogenetic approach to classification

Answer 4

Phenetic - grouped together based on overal similarity

Phylogenetic - grouped based on probable evolutionary relationships

Question 5

Genetic analysis is routinely used in the characterisation and identification of microorganisms. Why can the analysis of plasmid borne traits introduce errors?

Answer 5

• the potential loss of the plasmid from the bacterium of interest
• plasmid instability

Question 6

Detail the differences between rooted and uprooted phylogenetic trees and the difference in the relationships demonstrated in each type of tree?

Answer 6

Rooted - has node that serves as a common ancestor

Uprooted - represents a phylogenetic relationship but does not provide an evolutionary path

Question 7

What criteria must a gene meet to be used to create phylogenies?

Answer 7

• gene must be present in all organisms of interest
• gene cannot be subject to transfer between species
• gene must display appropriate level of sequence conservation

Question 8

Molecular chronometers are used to assess microbial phylogeny.
A). What is a molecular chronometer?
B). What assumptions are made for their use in microbial phylogeny?
C). What problems can occur with their use?

Answer 8

A). Nuclei acids or proteins used as clocks to measure the amount of evolutionary change over time.

B). Sequences gradually change over time without changing function, changes are selectively neutral and relatively random and the amount of change increases linearly with time.

C). Much more erratic than previously thought and can be almost useless to keep accurate evolutionary time. Can also often be problematic with a lack of fossil record.