BIMM 120 Lecture14.MicrobialEcologyII.051711

BIMM 120 Lecture14.MicrobialEcologyII.051711 - BIMM 120...

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Unformatted text preview: BIMM 120 Announcements BIMM 120 Announcements • HW#2 will be posted on WebCT in one week (Tues 5/24) ...due Tues May 31 ...Thursday ...Thursday ’s leftovers... s leftovers... Lecture 13 – Microbial Species & Evolution ☑ Biological Evolution on Earth- major events- early metabolisms- origins of life (where?)- evidence for early life □ Microbial Species Microbial Species How do we define a microbial species? How do we define a microbial species? How do microbial species evolve? How do microbial species evolve? extant species common ancestor The Microbial World The Microbial World (a SSU (a SSU rRNA rRNA view) view) LUCA (Last Universal Common Ancestor) LUCA (Last Universal Common Ancestor) Fast Fast-- forward a few billion years.... forward a few billion years.... • Our search for the LUCA continues to this day (very elusive!) • Without worrying about ancestral species, we still have a hard enough time trying to organize and define extant species! What is a microbial species? What is a microbial species? How do we define a microbial species? How do we define a microbial species? What metrics do we use? What metrics do we use? Is there a unified species concept for Bacteria & Archaea? Is there a unified species concept for Bacteria & Archaea? 16S rRNA gene sequence homology 97% identity DNA-DNA hybridization 70% hybridization genome wide Multi-Locus Sequence Typing (MLST) Sequence similarity among “housekeeping” genes Molecular Molecular-based analysis are a good start... based analysis are a good start... ...but they dismiss ecologically relevant criteria ...but they dismiss ecologically relevant criteria These are all the same “species” using molecular sequence analysis Let Let ’s take a further look at a selection of closely related species. s take a further look at a selection of closely related species. ... ... 97% 16S rRNA identity 70% DNA:DNA hybridization Multi Multi-Locus Sequence Typing (MLST) reliably separates these species Locus Sequence Typing (MLST) reliably separates these species • Biological Species Concept a species is an interbreeding population that is reproductively isolated from other interbreeding populations (Ernst Mayr – 1942) but microbes are NOT true “sexual species” (haploid) • Geneological Species Concept a species is a group of strains that cluster together phylogenetically & are distinct from other cohesive groups of strains “all true classification is geneological...” Charles Darwin, Origin of Species Typically this makes sense! A given species occupies a specific niche and A given species occupies a specific niche and has evolved to be successful in certain environments has evolved to be successful in certain environments • For example, their use of electron acceptors & donors, nutrients, etc....
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