Prokaryotes (Domains Bacteria & Archaea) KEY POINTS

Transcription

1 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

2 ANTIQUITY Cenozoic Humans Colonization of land >3.5 BILLION years old. Alone for 2 billion years Animals 1 4 Proterozoic Archaean Origin of solar system and Earth Prokaryotes 2 3 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen

3 General characteristics 1. Small: compare to µm for eukaryotic cell; single-celled; may form colonies. 2. Lack membraneenclosed organelles. 3. Cell wall present, but different from plant cell wall.

4 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.

5 General characteristics 5. Metabolic diversity established nutritional modes of eukaryotes.

6 General characteristics 6. Important decomposers and recyclers

7 General characteristics 6. Important decomposers and recyclers Form the basis of global nutrient cycles.

8 General characteristics 7. Symbionts!!!!!!! Parasites Pathogenic organisms. About 1/2 of all human diseases are caused by Bacteria

9 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.

10 General characteristics 7. Symbionts!!!!!!! Commensalists They are everywhere (really). There can be 10 million cells per square centimeter of skin.

11 General characteristics 7. Symbionts!!!!!!! Mutualists Eukaryotic life would be impossible without this.

12 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

13 General characteristics 7. Symbionts!!!!!!! Mutualists Mealybug endosymbionts with endosymbionts.

14 7. Symbionts!!!!!!! Mutualists General characteristics 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.

15 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.

16 Current taxonomy is Note that Prokaryote is paraphyletic. Why? Two Domains: Archaea: extremophiles (mostly), ancient, probable progenitors of eukaryotes. Bacteria: most commonly-encountered prokaryotes. stabilizing

17 Characteristics Cell Surface Motility Genome Reproduction & Growth Metabolic Diversity Nitrogen Metabolism Oxygen Relationships

18 Cell Surface Archaea: plasma membrane of ether-lipids (unique in life). Bacteria: a sugar polymer - peptidoglycan

19 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).

20 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.)

21 Genome Small genomes: ~1/1000th DNA content of eukaryotes. No membrane enclosed nucleus. DNA concentrated in nucleoid region.

22 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

23 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

24 Genome: Recombination via DNA taken up from the environment transformation

25 Genome: Recombination via Direct transfer of DNA between cells. Both plasmids and portions of bacterial chromosome. conjugation

26 Genome: Recombination via Transfer of DNA via phage viruses. transduction

27 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

28 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.

29 Metabolic Diversity: Source of Carbon AUTOTROPHS: Need only carbon dioxide (CO 2 ) as carbon source Metabolism HETEROTROPHS: Need at least one organic nutrient as carbon source (e.g. glucose; petroleum) Both of these present in domain Eucarya as well.

30 Metabolic Diversity: Source of Energy Metabolism PHOTOTROPHS: Need only sunlight as energy source CHEMOTROPHS: Derive energy from oxidation of organic molecules. Both of these present in domain Eucarya as well.

31 Metabolism Metabolic Diversity: Combined Energy Source: Sun Environment Carbon Source: CO 2 Photoautotroph Chemoautotroph Organic molecules Photoheterotroph Chemoheterotroph Which of these are present in multicellular Eucarya?

32 Metabolism Photoautotrophs Use sun for energy, CO 2 for carbon. Photosynthetic bacteria (e.g. cyanobacteria). Present in many plants and singlecelled Eucarya

33 Metabolism Chemoautotrophs Oxidize inorganics (H 2 S, NH 3 ) for energy. Need only CO 2 as carbon source. Unique to Bacteria and Archaea. E.g. Methanococcus jannaschii lives on hydrothermal vents at 2600m below sea level. Reduces H 2 + CO 2 to CH 4 + 2H 2 O.

34 Metabolism Photoheterotrophs Get enery from light but must obtain carbon in organic form (NOT CO 2 ). Unique to Bacteria and Archaea. E.g. Halobacterium salinarium.

35 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

36 Metabolism Nitrogen metabolism Nitrogen fixation: The only* mechanism that makes atmospheric Nitrogen available to other organisms. Convert N 2 into ammonia (NH 3 ) which is quickly protonated into ammonium (NH 4+ ). Essential for multicellular life!

37 Oxygen Relationships Aerobic vs. Anaerobic Obligate aerobes: use O 2 for cellular respiration. Facultative anaerobes: use O 2 if it is present by carry out anaerobic respiration or fermentation in anaerobic environment. Obligate anaerobes: poisoned by O 2 ; use anaerobic respiration or fermentation. Cellular respiration: Carbohydrates + O 2 CO 2 + H 2 O + energy Fermentation: Carbohydrates CO 2 + ethanol + energy Anaerobic respiration: Carbohydrates + [X] bicarbonate + [X - ] + energy Where [X] is a substance other than O 2 that accepts electrons such as nitrates or sulfates

38 Oxygen Relationships Early life (during the Archaean) was primarily anaerobic. Evolution of photosynthesis in Cyanobacteria changed all this.

39 Taxonomy of Prokaryotes Archaea or Archaebacteria Methanogens Halophiles Thermophiles Bacteria or Eubacteria Protobacteria Chlamyidias Spirochetes Cyanobacteria Gram-positive bacteria

40 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

41 Archaea or Archaebacteria Methanogens Use H 2 to reduce CO 2 to methane (CH 4 ). Chemoautotrophs Anaerobic In swamps, marshes, deep sea vents, important decomposers.

42 Archaea or Archaebacteria Halophiles Saline environments. Salinity several times higher than sea water. Photoheterotrophs

43 Archaea or Archaebacteria Thermophiles 60º-80ºCpH 2-4 optimal Chemoautotrophs Oxidize HS

44 Bacteria or Eubacteria Grouped by molecular systematics.

45 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

46 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

47 Bacteria or Eubacteria Cyanobacteria: Photoautotrophs Only prokaryotes with plant-like, O 2 -generating photosynthesis. Present in freshwater and marine environments. Often colonial--first steps toward multicellularity?

48 Bacteria or Eubacteria Spirochetes: Helical Recall motility: move by means of rotating, internal, flagellum-like filaments. Free-living and parasitic. Chemoheterotrophs (like us).

49 Bacteria or Eubacteria Chlamydias: ALL are parasites of animals. Intercellular. Lack peptidoglycan in the cell wall (are they gram-positive or gram-negative?). Most common form of STD in USA (urethritis).

50 Prokaryotes: Summary You should now have a good sense of prokaryote biology and diversity. Including roles in metabolism, symbioses, global energy cycles. Important distinguishing characteristics of cell wall, motility, genome, replication. General aspects of their systematics.