Microbiology Exam 1 - Bacterial Species

What is Linnean's definition of species?

an interbreeding population that is reproductively isolated

Why does Linnean's definition of species fail?

because bacteria don't sexually reproduce

What are the 6 types of bacterial classification strategies?

numerical taxonomy, DNA-DNA hybridization, phylogenetics, polyphasic approaches, naming by disease they cause, naming by serotype

What is numerical taxonomy based on?

trait similarity

How does numerical taxonomy work?

take traits and convert them to yes or no qualifiers and make pairwise comparisons, use similarity coefficient to determine how closely related they are

What are advantages of numerical taxonomy?

trait information is useful and meaningful

What are disadvantages of numerical taxonomy?

trait choice is arbitrary, all traits weighed equally, some traits are simple and some complex, traits aren't necessarily related to one another, some traits may arise through different mechanisms

What is DNA-DNA hybridization based on?

entire genome comparisons

What are advantages of DNA-DNA hybridization?

extremely accurate and relevant, only formal definition of bacterial species today

What are disadvantages of DNA-DNA hybridization?

organisms being compared must be very genetically similar for technique to be meaningful, cumbersome and impractical

What is phylogenetics based on?

evolutionary relatedness by sequence similarity

How do phylogenetics work? what do you use

use molecular chronometer

What is a molecular chronometer?

a sequence of a protein or gene sequence used to measure similarity among organisms, bacteria evolve over time so sequence of molecular chronometer slowly changes - organisms with fewer changes in sequence are more closely related

What are the criteria for molecular chronometer?

found in all representatives of a group being studied, function must be the same, sufficient similarity between molecules so sequences can be aligned, sufficient differences such that each sequence has its own signature

What are polyphasic approaches?

any combination of numerical taxonomy, DNA-DNA hybridization, and phylogenetics

How do polyphasic approaches work?

isolate and grow new bacterium by 1) sequence 16S rRNA and compare to a database to find closest relative - molecular chronometer 2) compare physical traits to closest "type strain" - numerical taxonomy 3) compare genome to type strain to determine same of different species - DNA-DNA hybridization

How does naming strains by serotype work?

strains are variants within a species so serotypes name pathogens based on antigen variation, antibodies bind and target antigens

What type of bacterial classification is 16S rRNA sequencing?

phylogenetics - 16S rRNA is a molecular chronometer

What is 16S rRNA?

nucleic acid sequence, found in all living things, part of ribosomes, relatively constant regions, highly variable regions

What are the consequences of 16S rRNA?

new tree of life (3 kingdoms - bacteria now parallel and equal to eukaryotes), new Archaea domain, revolutionized microbial ecology (quickly assess microbial numbers of an environment so can deduce properties by bacterial groups), endosymbiotic theory (organelles once bacteria)

What are the advantages of 16S rRNA sequencing?

easy in the sequencing age, massive data sets accumulating, fantastic for higher order comparisons

What are the disadvantages of 16S rRNA sequencing?

poor at species designation, no direct trait information

What is a bacterial species?

a collection of strains that share important traits and 70% DNA/DNA genome hybridization with a type strain

What is a type strain?

an arbitrarily selected bacterial strain that has all the hallmark traits of the species to which it belongs