LECTURE 1OMICROBIAL EVOLUTION &ClassificationFig. 10.14 StromatolitesFossilized, photosynthetic, microbial mats• The Earth is about 4.5 billion years old.• Microorganisms have been around for about 4billion years.• The early Earth was anoxic and much hotter.• The evidence suggests that biologicallyimportant molecules could be formed whengaseous mixtures like the primitive Earthare irradiated or shocked.The earliest “organisms” probably did not haveany DNA. They consisted of RNA and just a few,if any proteins.When self-replicating RNA molecules becameenclosed in membranes, they became the firstcellular life forms.Soon, proteins become main cellular enzymes.Using DNA as the genome likely resulted fromthe need to store genetic information in a morestable form.Evolution of Life - a Time ScaleWhat is the origin of eukaryotes?Many theories e.g.:1) Archaea-like cells evolved a nucleus,endomembranes, and cytosketeton.2) Endosymbiotic theory: Archaea like cellengulfed a Gram - bacterium = mitochondrionor a cyanobacterium = chloroplastSee next slide and read Perspective 3.1 onpage 76The Evolution of EndosymbiosisClassifying MicroorganismsThe grouping of organisms according todistinguishing characteristics that theyshare.Why is taxonomy and systemmatics important?1) Allows information to be organized so it canbe easily accessed by all in the scientificcommunity.2) By knowing properties and characteristics, wecan make predictions about related organisms.(“model organisms”)3) Allows for a common language. Enforces strictrules.4) Essential to accurately identify organisms.History of attempts to classify microbes..A little after the time of Leeuwenhoek (lec. 2),Linnaeus tried to classify all living things1759, named all known organismsusing the binomial system (Genus species).divided the world intoAnimal, Vegetable and MineralNot much was known about microbes at thattime so Linnaeus gave up in frustration andput all microscopiclife into one genus, Chaos!Whittaker (1969) and others 5 kingdom system: Plants, Animals, Fungi, Protists and Bacteria 3 main modes of nutrition: photosynthesis, adsorption, and ingestion show foot tree (next slide)This tree of life has been widely accepted but it is not phylogenetically correct. Archaea??NotmonophyleticWhat is monophyly?Monophyletic groupNot a monophyletic groupFig. 10.1. The 3-Domain system used inmodern biologyTable 10.01An aside on taxonomic ranks and the binomialsystem…….Bacillus anthracis Proteus vulgarisB. SubtilisGenus species names should be in italicsor underlined… E. coli or E. coliThe Binomial SystemSystematicsThe science of characterizing and organizingliving things, hopefully in a phylogenetic(evolutionarily historical) way…See Figure 10.18Fig. 10.18Fig. 10.18.Example of aphylogenetictree.Nodes areancesteralbranchpoints orpoints ofcommonancestors.What are characters?The information used to compare organisms..• morphological characters• metabolic characters• molecular charactersMolecular Systematics……Less ambiguous esp. for microbesG+C content of DNA - useful for grouping BacteriaFig. 10.16G + C content may seem like a crude measure,but it’s proven to be quite valuable formicrobial taxonomy.But, it still doesn’t tell you anything about thesequence of the organisms’ DNA.Molecular characters - II. DNA-DNAhybridizationFig. 10.17Fig. 10.17. DNA-DNA hybriization Modern systematics is based on direct examination of the “blue prints” of lifei.e. DNA and RNA sequences…..The most useful sequences for classifying all forms of life are ribosomal RNA because they are:1)found in all forms of life2)change slowly (over evolutionary time)Figure 10.9Bacteria Archaea EukaryoteMolecular characters - III. Nucleic Acid SequencingSSU Ribosomal RNAFig.
View Full Document
Unlocking...