Discussion 2: Bacteria (Prokaryotes) PDF

BIOL227 Discussion 2: Bacteria (prokaryotes)  2 Chapter 27 Pages: 608-626 Bacteria: Taxonomy Bacteria Origin Eukarya...

BIOL227 Discussion 2: Bacteria (prokaryotes)  2 Chapter 27 Pages: 608-626 Bacteria: Taxonomy Bacteria Origin Eukarya Archaea Sequence Change Comparisons of ribosomal RNA sequences reveal a three domains tree of life, rendering the term “prokaryote” obsolete 3 Recall: Eras end with mass extinctions Archaean era ends with increasing oxygen, for most prokaryotes a toxicby product of photosynthesis 4 Bacteria: 1 of 3 domains Table 27.2 A Comparison of the Three Domains of Life 4 Bacteria: Generalizations Archaea: unique rRNA sequence, cell walls and phospholipids in plasma membrane Prokaryotes are mostly microscopic: ranging from 0.5-5µm for prokaryotes (10µm-100µm for eukaryotic cells. Most prokaryotes are unicellular, although some species form colonies Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms Earth’s first organisms were likely prokaryotes 5 Bacteria: Phylogeny Genetic analysis led to the division of prokaryotes into two domains, Bacteria and Archaea Molecular systematists continue to work on the phylogeny of prokaryotes Figure 27.15 A simplified phylogeny of prokary6 otes. Bacteria: Shapes Prokaryotic cells have variety of shapes Three most common shapes are spheres (cocci), rods (bacilli), and spirals 7 Figure 27.2 The most common shapes of prokaryotes.  4500 Bacteria: Size 4000 3500 3000 2500 2000 Asacell increases in size, its volume 1500 grows faster than its surface area: 1000 500 surface area increases by a factor of n2 0 1 2 3 4 5 6 7 8 9 10 volume increases by a factor of n3 S.A Volume Small cells have a greater surface area relative to volume 9 Bacteria: Size Why are prokaryotic cells so much smaller than eukaryotic cells? Cytoskeleton of eukaryotic cell Cell wall and plasma membrane of a bacterium The cytoskeleton offers eukaryotic cells compressive and tensile strength. Prokaryotic cells lack a cytoskeleton (or have a much less elaborate one). Without a well-developed cytoskeleton, cells are at the mercy of their environments: they can easily lyse. This means they need a cell wall to prevent themselves from lysing. A cell wall means a thicker barrier for diffusing molecules to cross! To protect the fragile prokaryotic cell, the outside of the plasma membrane 10 is bounded by a cell wall. This protection, came at the cost of size. Bacteria: Membranes To compensate for their small size and absence of organelles, some prokaryotes have highly folded plasma membranes. (Analogous to the endomembrane system of eukaryotic cells). These specialized membranes perform metabolic functions. Endomembrane system of eukaryotic cell Review (homework): Cell structure of prokaryotic vs euka10ryotic cell Bacteria: Cell Surface Structures Nearly all prokaryotic cells have a cell wall It maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides Archaea contain polysaccharides and proteins but lack peptidoglycan N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) Eukaryote cell walls are made of cellulose (plants) or chitin (fungi) https://www.youtube.com/watch?v=H4kkQvKsNzw 11 Bacteria: Cell Surface Structures Gram stain can be used to classify bacteria by cell wall composition Staining procedure developed by Hans Christian Gram in 19th century. Two types of bacteria cells: Gram-positive, Gram-negative The differential staining reflects differences in cell structures. Importance of each step in Gram staining? What makes cells stain differentially? 12 Dr. Madoka Gray-Mitsumune Bacteria: Cell Surface Structures Gram stain can be used to classify bacteria by cell wall composition Gram-positive bacteria have simpler walls with a large amount of peptidoglycan Gram-negative bacteria have less peptidoglycan and an outer membrane (often can be toxic) Figure 27.3 Gram staining1.3 Bacteria: Gram -ve 14 Bacteria: Gram +ve Wikipedia https://www2.gvsu.edu/chm463/toxi ns/Image1.jpg Staphylococcus aureus Bacilus anthracis Bacillus anthracis, the causeof anthrax Clostridium botulinum, the causeof botulism SomeStaphylococcus and Streptococcus, which can be pathogenic Mycoplasmas, the smallest known cells Many antibiotic resistant bacteria are Gram +ve 15 Bacteria: Cell Surface Structures A polysaccharide or protein layer called a Capsule (eg Klebsiella capsule covers many prokaryotes pneumoniae ) Some prokaryotes have fimbriae, which allow them to stick totheir substrate or other Fimbriae (eg Neisseri individuals in a colony gonorrhoeae ) Bacteria: Cell Surface Structures Aslimy extracellular matrix called biofilm Biofilms Embedded in the biofilm are many bacterial cells Eg Listeria alongwith polysaccharides, proteins, lipids and monocytogenes DNA. https://en.wikipedia.org/wiki/Biofilm#/media/File: Staphylococcus_aureus Cells can also be covered by flagella. Flagella can Flagella be scattered about the surface or concentrated at Eg Vibrio one or both ends of the cell. cholerae 16 https://previews.123rf.com/images/drmicrobe/dr microbe2111/drmicrobe211100046/177152083- scientific-image-of-motile-flagellated-bacteria- bacterium-stenotrophomonas-maltophilia-3d.jpg Bacteria: Endospores Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries Figure 27.6 An endospore. 17 Bacteria: Brainstorm questions Neisseria gonorrhoeae the causative agent of gonorrhea uses fimbriae to attach itself to mucus membranes. Do you expect a strain of Neisseria gonorrhoeae that does not have fimbriae be able to cause disease? Clostridium species make spores. Why do you think Clostridium difficile infections in hospitals are of great concern? 20 Bacteria: Ecological success Prokaryotes have considerable genetic variation Three factors contribute to this genetic diversity: Rapid reproduction Mutation Genetic recombination 21 Bacteria: Rapid reproduction and mutation Prokaryotes reproduce by binary fission, and offspring are generally identical Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population The high diversity that results from mutations and rapid reproduction allows for rapid evolution 22 Bacteria: Genetic Recombination Genetic recombination, combining of DNA from two sources, contributes to diversity Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation Movement of genes among individuals from different species is called: Horizontal gene transfer Transformation Transduction Conjugation 23 Bacteria: Transformation A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation https://s3-us-west-2.amazonaws.com/courses-images/wp- 22 content/uploads/sites/1950/2017/05/31183951/fig2.gif Bacteria: Transduction Transduction is the movement of genes between bacteria by bacteriophage (viruses that infect bacteria) Figure 27.11 Transduction. 23 Bacteria: Conjugation Conjugation is the process where genetic material is transferred between prokaryotic cells F plasmid: capacity to produce pili R plasmids carry antibiotic resistance genes Figure 27.12 Bacterial conjugation. https://www.genome.gov/sites/default/fil 24 es/media/images/tg/Plasmid.jpg Bacteria: Conjugation and Recombination Figure 27.13a Conjugation and recombination in E. coli. In bacteria, the DNA transfer is one-way Cells containing the F plasmid function as DNA A donor cell attaches to a recipient by a donors during conjugation pilus, pulls it closer, and transfers DNA Cells without the F factor function as DNA A piece of DNA called the F factor is recipients during conjugation required for the production of pili The F factor is transferable during conjugat2i5on Bacteria: Nutritional Modes Energy and carbon sources are combined to give four major modes of nutrition: Photoautotrophy Chemoautotrophy Photoheterotrophy Chemoheterotrophy Prokaryotes can be categorized by how they obtain energy and carbon Phototrophs obtain energy from light Chemotrophs obtain energy from chemicals Autotrophs use CO2 as carbon source Heterotrophs require an organic nutrient to make organic compounds Table 27.1 Major Nutritional Mode26s Bacteria: Roles of Oxygen 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 29 Bacteria: Ecological Interactions Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont Prokaryotes often form symbiotic relationships with larger organisms In mutualism, both symbiotic organisms benefit In commensalism, one organism benefits while neither harming nor helping the other in any significant way In parasitism, an organism called a parasite harms but does not kill its host Parasites that cause disease are called pathogens 30 Bacteria: Mutualistic Symbiosis Mutualistic Bacteria: Human intestines are home to about 500–1,000 species of bacteria Many of these are mutualists and break down food undigested by our intestines The number of bacteria living on or within humans has been estimated to be 10x larger than the number of human cells Functional role in health What do you think the impact of taking an antibiotic on your gut Figure 27.20 The Human Microbiome and Health 29 microbes? Bacteria: Mutualistic Symbiosis Nitrogen is essential for production of amino acids and nucleic acids Prokaryotes can metabolize nitrogen in a variety of ways In nitrogen fixation, some prokaryotes convert atmospheric nitrogen Root nodules of (N2) to ammonia (NH3) leguminous plants with Rhizobium Figure 27.16b Exploring Selected Soil bacterium Nitrosomonas, which Major Groups of Bacteria converts NH4+ to NO2– 30 Bacteria: Nitrogen Cycle 33 Bacteria: Electron Transfer 34 Bacteria: Cyanobacteria Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells In the cyanobacterium Anabaena, photosynthetic cells and specialized nitrogen-fixing cells called heterocysts exchange metabolic products 35 Figure 27.14 Metabolic cooperation in a prokaryote. Bacteria: Pathogens Group contains pathogens including Campylobacter, which causes blood poisoning, and Helicobacter pylori, which causes stomach ulcers Figure 27.16f Exploring Selected Major Groups of Bacteria 36 Bacteria: Pathogens These are parasites that live within animal cells Usually lack peptidoglycan cell wall Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission 37 Figure 27.16g Exploring Selected Major Groups of Bacteria  Bacteria: Pathogens Spirochetes helical heterotrophs Some are parasites, including Treponema pallidum, which causes syphilis, and Borrelia burgdorferi, which causes Lyme disease 38 Figure 27.16h Exploring Selected Major Groups of Bacteria Bacteria: Pathogens Pathogenic Bacteria Bacteria cause about half of all human diseases For example, Lyme disease caused by a bacterium (Borrelia) and carried by ticks Figure 27.21 Lyme disease. 37 https://www.cdc.gov/lyme/images/lifecycle-small.jpg?_=45466 Bacteria: Toxins Pathogenic bacteria typically cause disease by releasing exotoxins or endotoxins Exotoxins are secreted and cause disease even if prokaryote that produced them are not present Endotoxins are released only when bacteria die and their cell walls break down 40  Tetanus is a disease caused by an exotoxin produced from Clostridium tetani  Salmonella infection (LPS activates complement) Bacteria: Research and Technology Experiments using prokaryotes have led to important advances in DNA technology E. coli is used in gene cloning use of DNA polymerase from Pyrococcus furiosus in the PCR technique Applications of CRISPR-Cas9 system has already opened new lines of research on HIV virus Figure 27.22 CRISPR: Opening new avenues of research for treating HIV infection. CRISPR: Clustered regularly interspaced palindromic repeats Cas9: CRISPR-associated 43 Bacteria: Research and Technology Bacteria can be used to make natural plastics Polyhydroxyalkanoates and polylactic acids Figure 27.23 Bacteria synthesizing and storing PHA, a component of biodegradable plastics. 44 Bacteria: Research and Technology Prokaryotes are the principal agents in bioremediation, use of organisms to remove pollutants from environment Figure 27.24 Bioremediation of an oil spill. 45 Bacteria: Research and Technology Bacteria can be engineered to produce vitamins, antibiotics, and hormones 46 Bacteria: Biosphere Prokaryotes are so important that if they were to disappear the prospects for any other life surviving would be dim Chemical Recycling Prokaryotes play a major role in recycling of chemical elements between living and nonliving components of ecosystems Chemoheterotrophic prokaryotes function as decomposers, breaking down dead organisms and waste products 47 Bacteria: Nutrient Availability Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth In other instances, they can “immobilize” or decrease the availability of key plant nutrients No bacteria: 0.5 milligram Strain 1: 0.7 milligram Strain 2: just over 0.6 milligram Strain 3: almost 1.0 milligram. Figure 27.18 Impact of bacteria on soil nutrient availability. 48 Bacterium used: Burkholderia glathei Summary of key concepts regarding prokaryotes Structural and functional adaptations contribute to prokaryotic success Rapid evolution, mutation, and genetic recombination promote genetic diversity in prokaryotes Diverse nutritional and metabolic adaptations have evolved in prokaryotes Prokaryotes have radiated into a diverse set of lineages Prokaryotes play crucial roles in the biosphere Prokaryotes have both beneficial and harmful impacts on humans 49