species concepts Flashcards
name and describe the different ways to classify a species (4)
discuss problems with each approach
- over 20 sepcies concepts exist, all with different problems.
- it is important that scientists keep working to figure out a way, because classification is needed for conservation, illness research etc
- 10 million to 1 billion species estimate
- modelling suggests up to 100 million species may exist in a gram of soil
1) morphological;
- do the organisms have similar shape and structure
- limited for microbiology because many microbes look the same under the microscope; 20 species max
- if colony characteristics and phenotype traits are included then this increases the number of describable features (a few hundred) but not by much.
- this is also limited because not all microbes can be cultured (99%)
2) trophy approach; how an organism gets its energy and carbon
- heterotrophic (eats complex carbohydrates) vs autotrophic (makes its own complex carbohydrates from simplex substances like carbon dioxide)
- chemoorgano- (oxidation of organic compounds releases energy), chemolitho- (oxidation of inorganic compounds gives energy), photo- (uses light as an energy source)
- limited to 6 groups
3) biological species concept; those who can inbreed to produce fertile offspring are a species
- limitation:dogs and wolves could in theory reproduce but they never would
- no way of classifying asexual microbes
4)DNA; those with genetic similarity are considered a species. genetic similarity implies evolutionary relationship and similar niche occupation
i) the 16s ribosome subunit (SSU) is used as a chronometer (a measure of evolutionary change); if two organisms have above 97% similarity then there genome is likely to be above 70% similar
ii) DNA from two organisms are denatured and melted together causing hybridisation. when the DNA strands are pulled apart, the more energy required the more dissimilar the genomes are. melting curve is used to plot the amount of genetic similarity
- limitation: there have been exaples of above 97% 16s ribosome similarity but less than 70% genome similarity
- limitation: only looks at the similarity, not the difference
- limitation: the % cut off values are arbitary; humans and monkeys are 96% similar in terms of genomes but not a species
- limitation:16S ribosome sequecing lacks resolving power between closely related strains. 6 strains of S. agalacitae with 100% 16S similarity, over 70% genome similarity yet a unique set of genes in each which result in different virulence, resistance etc. underestimates prokaryotic diversity
iii) entire genome sequencing; takes 5 hours with next gen sequencing such as nanopore, pyrosequencing
discuss how organisms are classified
- the 5 kingdom system is inaccurate; the 3 domain system was adopted (bacteria, archaea, eukaryotes)
- the 3 domains system is inaccurate, eukaryotes emerged from within archaea
discuss how the time of divergence can be estimated
16S rRNA has 1500 bases
one base pair change occurs every 1 million years
97% rRNA similarity means 45 bases are different; diverged 50mya
what are curent estimations of microbe richness
between 10 million and 1 billion species
1 gram of soil contains 100 million species
in terms of the trophic approach to classification, what does chemolitho and chemoorgano mean
chemolitho; gains energy from oxidation of inorganic molecules
chemoorgano; gains energy from oxidation of organic molecules
what is the word for something which is used as a measure of evolutionary change
chronometer
apart from checking DNA similarity, what is one way to use the genetic approach to classify a species
denature and melt the genomes of two species together and then pull them apart; amount of energy needed signals the genetic similarity
what is the name of the species with has 6 strains which have above 97% rRNA similarity and above 70% genomic similarity yet have different virulence genes making them very different
S. Agalacitae
