Lecture 2: Microbial Diversity

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Last updated 5:37 PM on 8/29/26
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16 Terms

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About how much of Earth's biomass is made up of microbes?
About 60%
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How are cellular microbes divided?
Prokaryotes (Bacteria and Archaea) and eukaryotes (algae, fungi, and protozoa)
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What are the major acellular groups discussed in lecture?
Viruses and prions
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What does the Three-Domain Tree suggest about the origin of Eukarya?
Eukarya arose from the Archaeal lineage
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Why may the Ring of Life better represent eukaryotic origins?
Eukaryotes have mixed Archaeal and Bacterial ancestry
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How did eukaryotes arise according to the Ring of Life?
An Archaeal host engulfed a Bacterium that survived inside it through endosymbiosis and eventually contributed to mitochondria
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What does LUCA stand for?
Last Universal Common Ancestor; the shared ancestor from which all existing life ultimately descends
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What characteristics did LUCA have?
DNA as genetic material, proteins and RNA for catalysis, and a lipid membrane
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Where did LUCA most likely live?
In an environment similar to hydrothermal vents
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How did scientists determine how LUCA likely lived?
They narrowed shared Bacterial and Archaeal genes to 355 ancient genes and analyzed their functions
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What evidence suggested LUCA lived near hydrothermal vents?
Genes for hydrogen utilization and reverse gyrase, which is associated with modern extremophiles
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What is the taxonomic order from broadest to most specific for bacteria?
Domain → Phylum → Class → Order → Family → Genus → Species → Strain
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How is the 16S rRNA gene used to classify prokaryotes?
Sequence differences, especially in variable regions V1–V9, are compared to determine genetic relatedness
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What 16S rRNA similarity can indicate a new species?
Less than 97% similarity to a known species
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What should be done if two organisms have >97% 16S rRNA similarity but major phenotypic differences?
Compare their entire genomes to determine relatedness
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Why can't microscopic appearance alone reliably identify microbial species?
Similar-looking microbes can have major genetic and functional differences