Chapter 27 PP - BIOL 1120 PDF

BIOL 1120 Chapter 27 – Bacteria and Archaea Dr. Anna Beaudry Learning Outcomes By the end of this lecture, you should be able to… ▪ Define what characterizes a prokaryote. ▪ Describe the structural and functional adaptations that contribute to prokaryotic success. ▪ Understand what factors contribut...

BIOL 1120 Chapter 27 – Bacteria and Archaea Dr. Anna Beaudry Learning Outcomes By the end of this lecture, you should be able to… ▪ Define what characterizes a prokaryote. ▪ Describe the structural and functional adaptations that contribute to prokaryotic success. ▪ Understand what factors contribute to prokaryotic genetic diversity. ▪ Define what characterizes the group archaea. ▪ Describe each distinct group of archaea. What is a Prokaryote? Prokaryotes are single-celled organisms that lack a distinct nucleus and other membrane-bound organelles. ▪ Makeup domains Bacteria and Archaea ▪ Adapted to diverse and extreme environments ▪ The most abundant organisms on Earth ▪ The number of prokaryotes in a handful of soil is greater than the number of people who have ever lived! ▪ First organisms to inhabit Earth Bacteria Bacteria include the vast majority of prokaryotic species familiar to most people. ▪ There are about 16,000 known species of bacteria ▪ The actual number is estimated to be 700,000–1.4 million species Campbell Biology, Figure 27.17 Archaea Share certain traits with bacteria and other traits with eukaryotes They also have many unique characteristics and are categorized accordingly Extremophiles ▪ Halophiles – “salt-loving,” live in environments with high levels of salt ▪ Thermophiles – live in extremely hot environments Moderate environments ▪ Methanogens – produce methane as a waste product (many are in mutualistic relationships) Campbell Biology, Figure 27.17 Dead Sea in Israel Hot Spring in Yellowstone Cow Campbell Biology, Figure 27.1 Common Shape of Prokaryotes They have a variety of shapes including: ▪ Spheres (cocci) ▪ Rods (bacilli) ▪ Spirals Campbell Biology, Figure 27.2 Cell Surface Structures Cell wall – maintains shape, protects the cell, and prevents it from bursting in a hypotonic environment. ▪ Often made of peptidoglycan (network of sugar polymers) ▪ Most prokaryotes lose water and experience plasmolysis in hypertonic environments ▪ This is why salt is used as a preservative because water loss slows the reproduction of food-spoiling prokaryotes! Gram Staining Scientists use the Gram stain to classify bacteria by cell wall composition. ▪ Gram-positive bacteria – simpler walls with a large amount of peptidoglycan ▪ Stain darker ▪ Gram-negative bacteria – less peptidoglycan and more complex with an outer membrane that contains lipopolysaccharides ▪ Stain lighter Campbell Biology, Figure 27.3 Cell Surface Structures Capsule or Slim Layer – sticky layer of polysaccharide or protein surrounding the cell wall. ▪ Called capsule if well-defined and slim layer is not well organized ▪ Enable prokaryotes to adhere to their substrate or others in the colony ▪ Protect against dehydration ▪ Some enable the prokaryote to surpass immune system Campbell Biology, Figure 27.4 Cell Surface Structures Endospores – highly retractile and thick-walled structures formed inside the bacterial cell. ▪ Ensure the survival of the bacteria in adverse environments (such as nutrient deficiency) ▪ The cell copies its chromosome and surrounds it with a multilayered structure ▪ Endospores can withstand extreme conditions and remain viable for centuries Campbell Biology, Figure 27.5 Cell Surface Structures Fimbriae – hair-like appendages ▪ Enable them to stick to their substrate or other in colony Pili – longer hair-like appendages ▪ Pull cells together enabling the exchange of DNA Flagellum – a hair-like appendage that enables movement of the prokaryote ▪ Taxis is defined as the ability to move toward or away from a stimulus ▪ Chemotaxis – movement toward or away from a chemical stimulus ▪ Phototaxis – movement toward or away from a light stimulus ▪ Thigmotaxis – Movement toward or away from contact or touch stimulus Video: Prokaryotic flagella Internal Organization and DNA Prokaryotes lack complex compartmentalization. ▪ Some have specialized membranes that perform metabolic functions ▪ These are usually infoldings of the cell membrane Campbell Biology, Figure 27.8 Internal Organization and DNA Prokaryotes have little DNA. ▪ Have one circular chromosome ▪ Prokaryotes lack a nucleus, instead their chromosome is in the nucleoid with no membrane ▪ May also have smaller rings of independently replicating DNA called plasmids (typically only carrying a few genes) *Small differences in gene expression allow antibiotics to kill or inhibit bacterial cell growth without harming human cells Campbell Biology, Figure 27.9 Prokaryote Reproduction Reproduce by binary fission – separation of the parent cell into two new daughter cells. ▪ Can divide every 1-3 hours under optimal conditions ▪ Some species can produce a new generation every 20 minutes (a rate fast enough to outweigh Earth in two days!) The 3 Key Factors Three factors contribute to the high levels of genetic diversity observed in prokaryote populations: ▪ Rapid reproduction ▪ Mutation ▪ Genetic recombination Rapid Reproduction and Mutation ▪ Offspring are typically identical, but differences can arise through mutation ▪ Mutation rates are low ▪ But mutations accumulate rapidly with short generation times and large populations ▪ Thus, prokaryotes are highly evolved Campbell Biology, Figure 27.10 Genetic Recombination Genetic recombination – the combining of DNA from two sources ▪ Contributes to prokaryote diversity DNA from different individuals can be combined by: 1. Transformation 2. Transduction 3. Conjugation Horizontal gene transfer – movement of genes between individual prokaryotes of different species Transformation Prokaryotic cells incorporate foreign DNA taken up from their surroundings. ▪ Thus, changing the prokaryotic cell’s genotype and phenotype Example – A nonpathogenic cell could take up a piece of DNA carrying an allele for pathogenicity and replace its own allele with the foreign allele ▪ The resulting recombinant cell would be pathogenic Transduction Phages carry prokaryotic genes from one host cell to another. Transduction is generally an unintended result of the phage replicative cycle ▪ Phage does not have the necessary genetic material to reproduce on its own A recombinant cell results Campbell Biology, Figure 27.11 Conjugation and Plasmids Conjugation is the process through which DNA is transferred between two prokaryotic cells. ▪ Cells are temporarily joined ▪ In bacteria, the DNA transfer is always one way: ▪ One cell donates the DNA ▪ The other receives it In E. coli, conjugation occurs by the following steps: ▪ A pilus of the donor cell attaches to the recipient ▪ The pilus retracts, pulling the two cells together ▪ DNA is transferred through a temporary structure called the “mating bridge” Campbell Biology, Figure 27.12 Conjugation and Plasmids A piece of DNA called the F factor (F for fertility) is required for the production of pili ▪ The F factor can exist either as a plasmid or a segment of DNA within the bacterial chromosome Cells containing the F plasmid (F+ cells) = DNA donors Cells lacking the F factor (F– cells) = recipients ▪ An F+ cell can convert an F– cell to an F+ cell if it transfers an entire F plasmid to the F– cell ▪ If only part of the F plasmid’s DNA is transferred, the recipient cell will be recombinant Campbell Biology, Figure 27.13 Recombinant Recipient Cells Cells that have the F factor in their chromosome (Hfr cells, named for high frequency of recombination) function as donors during conjugation ▪ Homologous segments of the chromosomal DNA from the Hfr cell recombines with that of the F– cell ▪ The recombinant recipient cell becomes a new genetic variant! Campbell Biology, Figure 27.14 R Plasmids and Antibiotic Resistance “Resistance genes” are carried by R plasmid (resistance) ▪ Some R plasmids carry genes for resistance to multiple antibiotics ▪ R plasmids also have genes that encode the pili used to transfer DNA between cells, enabling the rapid spread of resistance Nutritional and Metabolic Adaptations Prokaryotes can be categorized by how they obtain energy and carbon: ▪ Phototrophs obtain energy from light ▪ Chemotrophs obtain energy from chemicals ▪ Autotrophs require CO2 or related compounds as a carbon source ▪ Heterotrophs require an organic nutrient to make other organic compounds Nutritional and Metabolic Adaptations Energy and carbon sources are combined to give four major modes of nutrition: ▪ Photoautotroph ▪ Chemoautotroph ▪ Photoheterotroph ▪ Chemoheterotroph Campbell Biology, Table 27.1 The Role of Oxygen in Metabolism Prokaryotic metabolism varies with respect to the need for O2: ▪ Obligate aerobes require O2 for cellular respiration ▪ Obligate anaerobes are poisoned by O2 and live by fermentation or use substances other than O2 for anaerobic respiration ▪ Facultative anaerobes can use O2 if it is present or carry out fermentation or anaerobic respiration if not What is this dog an example of? Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids in all organisms ▪ Prokaryotes metabolize nitrogen in many forms ▪ Example – some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) in a process called nitrogen fixation Metabolic Cooperation Prokaryote cells may cooperate together to use resources unavailable to individual cells Example – surface–coating colonies called biofilms ▪ Cells near the edge release signaling molecules to recruit new cells ▪ Channels in the biofilm allow nutrients to reach cells in the interior and wastes to be expelled Can cause many problems for humans! ▪ Corrosion of industrial structures and products ▪ Contamination of medical devices ▪ Tooth decay ▪ Chronic, antibiotic-resistant infections The Role of Prokaryotes in the Biosphere Crucial for the survival of all life on Earth! But can also be harmful. A few examples: ▪ Chemical recycling ▪ Ecological interaction ▪ Mutualistic bacteria ▪ Pathogenic bacteria Chemical Recycling Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of the environment. ▪ Decomposers – break down dead organisms and waste and release carbon Prokaryotes can convert some molecules into usable forms for other organisms ▪ Autotrophic prokaryotes use CO2 to produce sugars and O2 that are consumed by other organisms ▪ Nitrogen-fixing bacteria transform atmospheric nitrogen into forms available to other organisms ▪ Some prokaryotes can increase the availability of soil nutrients that plants require for growth Campbell Biology, Figure 27.19 Ecological Interactions Symbiosis is an ecological relationship in which two species live in close contact, a larger host with a smaller symbiont. ▪ Prokaryotes often form symbiotic relationships with larger organisms Types of relationships: ▪ Mutualism – both symbiotic organisms benefit ▪ Commensalism – one organism benefits while neither harming nor helping the other ▪ Parasitism – an organism called a parasite harms but does not usually kill its host ▪ Parasites that cause disease are called pathogens Mutualism – bacterial “headlights” Campbell Biology, Figure 27.20 Mutualistic Bacteria Human intestines are home to about 500–1,000 species of bacteria ▪ Intestinal bacteria cells collectively outnumber all human cells in the body by a factor of ten! Many intestinal bacteria are mutualists ▪ Involved in synthesizing carbohydrates, vitamins, and other important nutrients ▪ Produces signals that activate human genes involved in absorption and antimicrobial production Other Beneficial Uses of Bacteria Humans reap many benefits from bacteria including the production of many foods: ▪ Cheese and yogurt from milk ▪ Beer and wine ▪ Pepperoni ▪ Fermented cabbage (sauerkraut) ▪ Soy sauce Other uses: ▪ To produce natural plastics ▪ To produce ethanol from agricultural waste, switchgrass, and corn ▪ Bioremediation – the use of organisms to remove pollutants from soil, air, or water Pathogenic Bacteria All known pathogenic prokaryotes are bacteria ▪ Bacteria cause about half of all human diseases ▪ Indirect vs. direct transmission Example – Lyme disease (Borrelia burgdorferi) ▪ Carried by fleas or ticks ▪ If left untreated, can cause arthritis, heart disease, nervous disorders, and death ▪ Infects about 300,000 people per year in the United States Campbell Biology, Figure 27.21 Pathogenic Bacteria Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins Exotoxins – proteins secreted by bacteria that can cause disease even if the bacteria are no longer present ▪ Example – Cholera Endotoxins – lipopolysaccharide components of the outer membrane of gram-negative bacteria ▪ They are released only when bacteria die and their cell walls break down ▪ Example – Salmonella Pathogenic Bacteria Horizontal gene transfer can spread genes associated with virulence to normally harmless bacteria For example, E. coli ▪ Normally a harmless gut symbiont in the human intestines ▪ Pathogenic strains were produced by phase-mediated transfer of genes from pathogenic species ▪ 75,000 cases per year in the US alone Learning Outcomes ▪ Define what characterizes a prokaryote. ▪ Describe the structural and functional adaptations that contribute to prokaryotic success. ▪ What factors contribute to prokaryotic genetic diversity? ▪ Define what characterizes the group archaea. ▪ Describe each distinct group of archaea.