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UMass Amherst MICROBIO 310 - The Evolution and Diversity of Microbes

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MICROBIO 310 1st Edition Lecture 5Outline of Last Lecture I. 1.9 The Rise of Microbial DiversityII. 1.10 The Modern Era of MicrobiologyIII. 2.1 Some Principles of Light MicroscopyIV. 2.2 Improving Contrast in Light MicroscopyV. 2.3 Imaging Cells in Three DimensionsVI. 2.4 Electron MicroscopyOutline of Current Lecture I. 2.5 Elements of Microbial StructureII. 2.6 Arrangement of DNA in Microbial CellsIII. 2.7 The Evolutionary Tree of LifeIV. 2.8 Metabolic Diversity V. 2.9 Bacteria VI. 2.10 Archaea VII. 2.11 Phylogenetic Analyses of Natural Microbial Communities VIII. 2.12 Microbial EukaryaThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Current Lecture2.5 Elements of Microbial Structure • Eukaryotic vs. Prokaryotic Cells– Eukaryotes• DNA enclosed in a membrane-bound nucleus • Cells are generally larger and more complex • Contain organelles– Prokaryotes• No membrane-enclosed organelles, no nucleus • Generally smaller than eukaryotic cells• Viruses – Not considered cells but are alive– No metabolic abilities of their own– Rely completely on biosynthetic machinery of infected cell– Infect all types of cells– Smallest virus is 10 nm in diameter2.6 Arrangement of DNA in Microbial Cells• Genome– A cell’s full complement of genes• Prokaryotic cells generally have a single, circular DNA molecule called a chromosome– DNA aggregates to form the nucleoid region– Prokaryotes also may have small amounts of extra-chromosomal DNA called plasmids that confer special properties (e.g., antibiotic resistance)• Eukaryotic DNA is linear and found within the nucleus– Associated with proteins that help in folding of the DNA– Usually more than one chromosome– Typically two copies of each chromosome– During cell division, nucleus divides by mitosis (does not happen in bacteria)– During sexual reproduction, the genome is halved by meiosis (bacteria do have sex)• Escherichia coli Genome– 4.64 million base pairs– 4,300 genes– 1,900 different kinds of protein – 2.4 million protein molecules• Human Cell– 1,000x more DNA per cell than E. coli– 7x more genes than E. coli2.7 The Evolutionary Tree of Life• Evolution– The process of change over time that results innew varieties and species of organisms (i.e. antibiotic resistance)• Phylogeny– Evolutionary relationships between organisms– Relationships can be deduced by comparing genetic information in different specimens– Ribosomal RNA (rRNA) is excellent for determining phylogeny– Relationships visualized on a phylogenetic tree• Comparative rRNA sequencing has defined three distinct lineages of cells called domains: – Bacteria(prokaryotic)– Archaea (prokaryotic)– Eukarya(eukaryotic) • Archaeaand Bacteriaare NOT closely related • Archaeaare more closely related to Eukaryathan Bacteria • Eukaryotic microorganisms were the ancestors of multicellular organisms• Mitochondria and chloroplasts also contain their own genomes (circular, like prokaryotes) and ribosomes– These organelles are related to specific lineages of Bacteria– They used to be free swimming bacteria– Mitochondria and chloroplasts took up residence in Eukarya eons agoEukarya engulfed the free swimming bacteria now Eukarya have a double membrane• This arrangement is known as endosymbiosis2.8 Metabolic Diversity• Chemoorganotrophs– Obtain their energy from the oxidation of organic molecules (i.e. glucose, acetate, etc.)– Aerobes use oxygen to obtain energy– Anaerobes obtain energy in the absence of oxygen• Chemolithotrophs– Obtain their energy from the oxidation ofinorganic molecules (i.e. H2, H2S, Fe2+, NH4+ etc.)– Process found only in prokaryotes•  Phototrophs– Contain pigments that allow them to use lightas an energy source– Oxygenic photosynthesis produces oxygen– Anoxygenic photosynthesis does not produce oxygen• All cells require carbon as a major nutrient– Autotrophs• Use carbon dioxide as their carbon source• Sometimes referred to as primary producers (i.e. plants)– Heterotrophs• Require one or more organic molecules fortheir carbon source• Feed directly on autotrophs or live off products produced by autotrophs(i.e. humans)• Organisms that inhabit extreme environmentsare called  extremophiles• Habitats include boiling hot springs, glaciers, extremely salty bodies of water, and high-pH environments- Advantage to living in extreme environments: less competition2.9 Bacteria• The domain Bacteria contains an enormousvariety of prokaryotes• All known pathogenic prokaryotes are Bacteria• The Proteobacteria make up the largest phylum of Bacteria– Gram-negative• Examples: E. coli, Pseudomonas, and Salmonella• Gram-positive phylum united by phylogeny and cell wall structure- Cyanobacteria are relatives of gram-positive bacteria• Many Other Phyla of Bacteria – Green sulfur bacteria and green nonsulfur bacteria are photosynthetic– Deinococcusis extremely resistant to radioactivity– Chlamydia are obligate intracelluar parasites 2.10 Archaea• Two Phyla of the Domain Archaea– Euryarchaeota• Methanogens:degradeorganicmatteranaerobically; produce methane (natural gas)• Extremehalophiles:requirehighsalt concentrations for metabolism and reproduction• Thermoacidophiles: grow in moderately high temperatures and low-pH environments–  Crenarchaeota• Vast majority of cultured Crenarchaeota are hyperthermophiles• Some live in marine, freshwater, and soil systems– Archaea are more likely to live in extreme environments2.11 Phylogenetic Analyses of Natural Microbial Communities• Microbiologists believe that we have cultured only a small fraction of the Archaea and Bacteria• Studies done using methods of molecular microbial ecology, devised by Norman Pace– Microbial diversity is much greater than laboratory culturing can reveal2.12 Microbial Eukarya• Eukaryotic microorganisms include algae, fungi,protozoa, and slime molds– Protists include algae and protozoa• Algae are phototrophic• Protozoa are NOT phototrophic – Fungi are decomposers – Algae and fungi have cell walls, whereas protozoa and slime molds do not• Lichens are a mutualistic relationship between two groups of protists – Fungi and cyanobacteria– Fungi and


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