2/4/15 Prokaryotes (Domains Bacteria & Archaea) KEY POINTS 1. Decomposers: recycle organic and inorganic molecules in environment; makes them available to other organisms. 2. Essential components of symbioses. 3. Encompasses the origins of metabolism and metabolic diversity. 4. Origin of photosynthesis and formation of atmospheric Oxygen Ceno- Meso- zoic zoic ANTIQUITY Humans Paleozoic Colonization of land Animals Origin of solar system and Earth • >3.5 BILLION years old. • Alone for 2 1 4 billion years Proterozoic Archaean Prokaryotes Billions of 2 years ago3 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen General characteristics 1. Small: compare to 10-100µm for 0.5-5µm eukaryotic cell; single-celled; may form colonies. 2. Lack membrane- enclosed organelles. 3. Cell wall present, but different from plant cell wall. 1 2/4/15 General characteristics 4. Occur everywhere, most numerous organisms. – More individuals in a handful of soil then there are people that have ever lived. – By far more individuals in our gut than eukaryotic cells that are actually us. General characteristics 5. Metabolic diversity established nutritional modes of eukaryotes. General characteristics 6. Important decomposers and recyclers 2 2/4/15 General characteristics 6. Important decomposers and recyclers • Form the basis of global nutrient cycles. General characteristics 7. Symbionts!!!!!!! • Parasites • Pathogenic organisms. • About 1/2 of all human diseases are caused by Bacteria General characteristics 7. Symbionts!!!!!!! • Parasites • Pathogenic organisms. • Extremely important in agriculture as well. Pierce’s disease is caused by Xylella fastidiosa, a Gamma Proteobacteria. It causes over $56 million in damage annually in California. That’s with $34 million spent to control it! = $90 million in California alone. 3 2/4/15 General characteristics 7. Symbionts!!!!!!! • Commensalists • They are everywhere (really). • There can be 10 million cells per square centimeter of skin. General characteristics 7. Symbionts!!!!!!! • Mutualists • Eukaryotic life would be impossible without this. General characteristics 7. Symbionts!!!!!!! • Mutualists • Allows herbivorous (plant-feeding) animals to digest cellulose and other low-quality plant tissues. • Termites • Ungulates “chewing the cud” • Lagomorph coprophagy 4 2/4/15 General characteristics 7. Symbionts!!!!!!! • Mutualists • Mealybug endosymbionts with endosymbionts. General characteristics 7. Symbionts!!!!!!! • Mutualists • Komodo dragons and their “toxins”. • Hunt large prey and can inflict fairly minor wound. • Prey die fairly quickly from wound. • Infection by highly pathogenic Pasteurella multocida (Gamma Proteobacteria). • Prominent in saliva of dragons, but dragons have an anti- Pasteurella antibody. TAXONOMY is problematic • Relationships obscured by billions of years of evolution • Also obscured by unique bacterial means of recombination (more later). • Grouped primarily by DNA sequence data. • Immense genetic/genomic diversity. 5 2/4/15 Current taxonomy is stabilizing • Note that “Prokaryote” is paraphyletic. Why? • Two Domains: • Archaea: extremophiles (mostly), ancient, probable progenitors of eukaryotes. • Bacteria: most commonly-encountered prokaryotes. Characteristics • Cell Surface • Motility • Genome • Reproduction & Growth • Metabolic Diversity • Nitrogen Metabolism • Oxygen Relationships Cell Surface • Archaea: plasma membrane of ether-lipids (unique in life). • Bacteria: a sugar polymer - peptidoglycan 6 2/4/15 Cell Surface • Cell wall is often modified with structures to adhere to substrate. • Many secrete a sticky capsule or adhere by fimbriae (ocasionally called pili). Motility • ~half the species can move. 1. Flagella most common (different structure from eukaryote) 2. Spiral filaments: spirochetes corkscrew 3. Gliding over slimy secretions (via flagellar motors without filament) • Capable of taxis (photo, chemo, geo, etc.) Genome • Small genomes: ~1/1000th DNA content of eukaryotes. • No membrane enclosed nucleus. • DNA concentrated in ‘nucleoid’ region. 7 2/4/15 Genome • One major chromosome, double stranded DNA molecule in ring. • Sometimes several small DNA rings of few genes: plasmids. – Replicate independently of main chromosome. – Permit recombination via conjugation (later). – Involved in resistance to antibodies/antibiotics. Genome • Broadly, replication & translation of genetic info like that of eukaryotes; differ in details and simplicity. • Used in first DNA recombinant research. • Genetic recombination: Not like eukaryotes (e.g. chiasma & crossing over)!! – Transformation – Conjugation – Transduction Genome: Recombination via transformation • DNA taken up from the environment 8 2/4/15 Genome: Recombination via conjugation • Direct transfer of DNA between cells. • Both plasmids and portions of bacterial chromosome. Genome: Recombination via transduction • Transfer of DNA via phage viruses. Reproduction & Growth • Meiosis & Mitosis NOT PRESENT. • Asexual binary fission. • DNA replication can be nearly continuous in ideal conditions (depends on pH, salinity, temperature, etc.) • Generation times as fast as 20 minutes 9 2/4/15 Metabolism Metabolic Diversity • Nutrition: • Requires a source of carbon for synthesizing organic compounds: either carbon dioxide or living matter. • Requires a source of energy to drive reactions: either light or chemical. Metabolic Diversity: Metabolism Source of Carbon • AUTOTROPHS: Need only carbon dioxide (CO2) as carbon source • HETEROTROPHS: Need at least one organic nutrient as carbon source (e.g. glucose; petroleum) • Both of these present in domain Eucarya as well. Metabolic Diversity: Metabolism Source of Energy • PHOTOTROPHS: Need only sunlight as energy source • CHEMOTROPHS: Derive energy from oxidation of organic molecules. • Both of these present in domain Eucarya as well. 10 2/4/15 Metabolism Metabolic Diversity: Combined Energy Source: Sun Environment Photoautotroph Chemoautotroph CO2 Source: Source: Carbon Organic Photoheterotroph Chemoheterotroph molecules Which of these are present in multicellular Eucarya? Metabolism Photoautotrophs • Use sun for energy, CO2 for carbon. • Photosynthetic bacteria (e.g. cyanobacteria). • Present in many plants and single- celled Eucarya Metabolism Chemoautotrophs • Oxidize inorganics (H2S, NH3) for energy. • Need only CO2 as carbon source. • Unique to Bacteria and Archaea. • E.g. Methanococcus jannaschii lives on hydrothermal vents at 2600m below sea level. • Reduces H2 + CO2 to CH4 + 2H2O. 11 2/4/15 Metabolism Photoheterotrophs • Get enery from light but must obtain carbon in organic form (NOT CO2). • Unique to Bacteria and Archaea. • E.g. Halobacterium salinarium. Metabolism Chemoheterotrophs • Consume organic molecules for both energy and carbon. • Common among prokaryotes: – saprobes (decomposers) – parasites (rely on living hosts) • Also widespread in Protista, Animalia, Plantae. Metabolism Nitrogen metabolism • Nitrogen fixation: • The only* mechanism that makes atmospheric Nitrogen available to other organisms. • Convert N2 into ammonia (NH3) which is quickly protonated into + ammonium (NH4 ). • Essential for multicellular life! 12 2/4/15 Oxygen Relationships • Aerobic vs. Anaerobic • Cellular respiration: • Obligate aerobes: use O2 for – Carbohydrates + O2 →CO2 cellular respiration. + H2O + energy • Facultative anaerobes: use • Fermentation: O2 if it is present by carry out – Carbohydrates →CO2 + anaerobic respiration or ethanol + energy fermentation in anaerobic • Anaerobic respiration: environment. – Carbohydrates + [X] → • Obligate anaerobes: bicarbonate + [X-] + energy poisoned by O2; use – Where [X] is a substance anaerobic respiration or other than O2 that accepts fermentation. electrons such as nitrates or sulfates Oxygen Relationships • Early life (during the Archaean) was primarily anaerobic. • Evolution of photosynthesis in Cyanobacteria changed all this. Taxonomy of Prokaryotes • Archaea or Archaebacteria – Methanogens – Halophiles – Thermophiles • Bacteria or Eubacteria – Protobacteria – Chlamyidias – Spirochetes – Cyanobacteria – Gram-positive bacteria 13 2/4/15 Archaea or Archaebacteria • Live in extreme environments (extremophiles): sulfur hot springs, deep sea vents, high salt environments. • Lack peptidoglycan, unique plasma membrane of liquids • Likely sister group of Eukaryotes Archaea or Archaebacteria • Methanogens – Use H2 to reduce CO2 to methane (CH4). – Chemoautotrophs – Anaerobic – In swamps, marshes, deep sea vents, important decomposers. Archaea or Archaebacteria • Halophiles – Saline environments. – Salinity several times higher than sea water. – Photoheterotrophs 14 2/4/15 Archaea or Archaebacteria • Thermophiles – 60º-80ºCpH 2-4 optimal – Chemoautotrophs – Oxidize HS Bacteria or Eubacteria • Grouped by molecular systematics. Bacteria or Eubacteria Proteobacteria • VERY diverse, grouped into five taxa based on DNA sequence data. • Includes most types of metabolism that we’ve discussed. • Includes most of the types of symbioses we’ve discussed • Review the summary in Figure 27.16. 15 2/4/15 Bacteria or Eubacteria Gram positive Bacteria: • Simple peptidoglycan cell wall. • Rival Proteobacteria in diversity. • Most are free-living decomposers. • Some pathogenic (e.g. strains of Staphylococcus, Streptococcus, Bacillus anthracis, Clostridium botulinum). • Include the mycoplasms--the only bacteria that lack cell walls Bacteria or Eubacteria Cyanobacteria: • Photoautotrophs • Only prokaryotes with plant-like, O2-generating photosynthesis.