Bacteria and Archaea.pptx

Bacteria and Archaea  Bacteria and Archaea I. Prokaryotic Structure II. Prokaryote Reproduction III. Metabolism and Nutrition IV. Prokaryotic Diversity V. Ecological Importance  Learning Objectives 1. Compare the three main bacteria shapes 2. Describe the internal and external structu...

Bacteria and Archaea  Bacteria and Archaea I. Prokaryotic Structure II. Prokaryote Reproduction III. Metabolism and Nutrition IV. Prokaryotic Diversity V. Ecological Importance  Learning Objectives 1. Compare the three main bacteria shapes 2. Describe the internal and external structure of prokaryotes 3. Explain how the genetic material of a cell is organized (chromosome and plasmid DNA) 4. Describe prokaryotic reproduction 5. Explain the mechanisms that generate genetic diversity in bacteria 6. Describe the metabolism and nutrition among prokaryotes 7. Compare the characteristics of the Domains Bacteria and Archaea 8. Identify representatives for each of the main types of Archaea and Bacteria 9. Evaluate the ecological contributions of bacteria to life on Earth.  I. Prokaryotic Structure A. Size and shape 1. Most prokaryotic cells are 0.5–5 µm, much smaller than the 10– 100 µm of many eukaryotic cells 2. Prokaryotic cells have a variety of shapes 3. The three most common shapes are spheres (cocci), rods (bacilli), and spirals B. Surface Structures 1. An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment 2. Eukaryote cell walls are made of cellulose or chitin 3. Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross- linked by polypeptides 4. Archaea walls contain polysaccharides and proteins but lack peptidoglycan 5. Scientists use the Gram stain to classify bacteria by cell wall composition 6. Gram-positive bacteria have simpler walls with a large amount of peptidoglycan 7. Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic 8. Many antibiotics target peptidoglycan and damage bacterial cell walls 9. A polysaccharide or protein layer called a capsule covers many prokaryotes 10. Some prokaryotes have fimbriae, which allow them to stick to their substrate or other individuals in a colony 11. Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA C. Locomotion 1. Many bacteria exhibit taxis, the ability to move toward or away from a stimulus 2. Chemotaxis is the movement toward or away from a chemical stimulus 3. Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends 4. Bacterial flagella are composed of a motor, hook, and filament D. Internal Organization 1. Prokaryotic cells usually lack complex compartmentalization 2. Some prokaryotes do have in-foldings of the plasma membrane that perform metabolic functions 3. Most of the genome consists of a circular chromosomelocated in the nucleoid region 4. Some species of bacteria also have smaller rings of DNA called plasmids  II. Prokaryotic Reproduction A. General features of reproduction in bacteria: – They are small – They reproduce by binary fission (1-3 hours) – They have short generation times Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries B. Bacteria cannot reproduce sexually, however Three factors contribute to their genetic diversity:  Rapid reproduction  Mutation  Genetic recombination 1. Rapid reproduction and mutation Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population High diversity from mutations allows for rapid evolution 2. Genetic recombination a) A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation b) Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria) c) Movement of genes among individuals from different species is called horizontal gene transfer 3. Conjugation is the process where genetic material is transferred between prokaryotic cells a) In bacteria, the DNA transfer is one way b) A donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA c) A piece of DNA called the F factor is required for the production of pili  III. Metabolism and Nutrition A. Prokaryotes can be categorized by how they obtain energy and carbon – Phototrophs obtain energy from light – Chemotrophs obtain energy from chemicals – Autotrophs require CO2 as a carbon source – Heterotrophs require an organic nutrient to make organic compounds B. Energy and carbon sources are combined to give four major modes of nutrition: C. Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocysts (or heterocytes) exchange metabolic products D. Prokaryotic metabolism varies with respect to O2 – Obligate aerobes require O2 for cellular respiration – Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration – Facultative anaerobes can survive with or without O2 Gram positive, exotoxin producing bacterium  IV. Prokaryotic Diversity A. Domain Archaea 1. Archaea share certain traits with bacteria and other traits with eukaryotes 2. Some archaea live in extreme environments and are called extremophiles Extreme halophiles (Clade Euryarchaeota) live in highly saline environments Extreme thermophiles (Clade Crenarchaeota) thrive in very hot environments 3. Methanogens (Clade Euryarchaeota) live in swamps and marshes and produce methane as a waste product Methanogens are strict anaerobes and are poisoned by O2 B. Domain Bacteria 1. Proteobacteria These gram-negative bacteria include photoautotrophs, chemoautotrophs, and heterotrophs Some are anaerobic, and others aerobic 2. Chlamydia are parasites that live only within animal cells Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission 3. Spirochetes are helical heterotrophs Some are parasites, including Treponema pallidum, which causes syphilis, and Borrelia burgdorferi, which causes Lyme disease 4. Cyanobacteria are photoautotrophs that generate O2 5. Gram-positive bacteria include – Actinomycetes, which decompose organic matter – Bacillus anthracis, the cause of anthrax – Clostridium botulinum, the cause of botulism – Some Staphylococcus and Streptococcus, which can be pathogenic – Mycoplasms, the smallest known cells  V. Ecological Importance A. Chemical recycling 1. Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems 2. Chemoheterotrophic prokaryotes function as decomposers, breaking down dead organisms and waste products 3. Prokaryotes can increase the availability of nitrogen, phosphorus, and potassium for plant growth B. Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont 1. Prokaryotes often form symbiotic relationships with larger organisms 2. In mutualism, both symbiotic organisms benefit Human intestines are home to about 500–1,000 species of bacteria Many of these are mutualists and break down food that is undigested by our intestines C. Pathogenic bacteria 1. Prokaryotes cause about half of all human diseases i. For example, Lyme disease is caused by a bacterium and carried by ticks (Borrelia burgdorferii) 2. Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins  Exotoxins Vs. Endotoxins Endotoxins are lipopolysaccharide molecules in the outer membrane of gram- negative bacteria. These toxins are only released when bacteria die and the outer membrane breaks down. (Salmonella typhi)  Exotoxins Vs. Endotoxins Vibrio cholerae Exotoxins are proteins certain bacteria secrete while performing their metabolism. Exotoxins can cause disease even after the bacteria that produced them are Gamma-proteobacteria no longer present. produce exotoxins