Prokaryotes PDF

2.2 Prokaryotes Prokaryotes Prokaryote = before nucleus Single-celled organism that lacks a nucleus and membrane bound organelles. Oldest, structurally simplest, and most abundant forms of life. Abundant for over a billion years before eukaryotes. 90 to 99% unknown and undescribed Less than 1% cause...

2.2 Prokaryotes Prokaryotes Prokaryote = before nucleus Single-celled organism that lacks a nucleus and membrane bound organelles. Oldest, structurally simplest, and most abundant forms of life. Abundant for over a billion years before eukaryotes. 90 to 99% unknown and undescribed Less than 1% cause disease Fall into 2 domains ○ ○ Bacteria (also called Eubacteria) Archaea (formerly called Archaebacteria) Prokaryotic Evolution Harsh conditions of early Earth ○ ○ Protective environments Extremophiles First life forms on Earth ○ ○ Microbial mat fossils date to 3.5 byo Energy from chemicals at hydrothermal vents A microbial mat. (a) This microbial mat, about one meter in diameter, is growing over a hydrothermal vent in the Pacific Ocean in a region known as the “Pacific Ring of Fire.” The mat’s colony of bacteria helps retain microbial nutrients. Chimneys such as the one indicated by the arrow allow gases to escape. (b) In this micrograph, bacteria are visualized using fluorescence microscopy. Prokaryotes are not a monophyletic group! Prokaryotic Diversity Figure 22.1 Certain prokaryotes can live in extreme environments such as the Morning Glory pool, a hot spring in Yellowstone National Park. The spring’s vivid blue color is from the prokaryotes that thrive in its very hot waters. (credit: modification of work by Jon Sullivan) Prokaryotic Diversity Figure 22.6 Halophilic prokaryotes. (a) The Dead Sea is hypersaline. Nevertheless, salt-tolerant bacteria thrive in this sea. (b) These halobacteria cells can form salt-tolerant bacterial mats. (credit a: Julien Menichini; credit b: NASA; scale-bar data from Matt Russell) Extremophiles Lovers of extremes Acidophiles: pH 3 or below Alkaliphiles: pH 9 or below Thermophiles: temperature 60-80 °C (140-176 °F) Hyperthermophiles: temperature 80-122 °C (176-250 °F) Psychrophiles: temperature -15-10 °C (5-50 °F) or lower Halophiles: salt concentration of at least 0.2 M Osmophiles: high sugar concertation Hypolith: low humidity/ water Characteristics of All Cells 1. 2. 3. 4. Plasma membrane Cytoplasm Double-stranded DNA genome Ribosomes Characteristics of Prokaryotic Cells All Unicellular ○ Form communities Single circular, double-stranded DNA chromosome Nucleoid: region (no envelope) of the cell that contains the genome Cell wall & plasma membrane Ribosomes Some Capsule Flagella Pili Figure 22.10 The features of a typical prokaryotic cell. Flagella, capsules, and pili are not found in all prokaryotes. Prokaryotic Cell Shapes Figure 22.9 Common prokaryotic cell types. Prokaryotes fall into three basic categories based on their shape, visualized here using scanning electron microscopy: (a) cocci, or spherical (a pair is shown); (b) bacilli, or rod-shaped; and (c) spirilli, or spiral-shaped. Prokaryotic Reproduction Asexually by binary fission Do not undergo mitosis Chromosome is replicated Cell pinches inward Two clone cells are created Horizontal gene transfer: transfer of genetic material from an organism to another organism not its offspring Can occur between different species Responsible for most of the genetic variation rather than mutations Can cause large-scale changes in a bacterial genome If transferred genes do not provide a selective advantage they are usually lost by deletion Prokaryotic Genetics Transformation: the cell takes up prokaryotic DNA directly from the environment. The DNA may remain separate as plasmid DNA or be incorporated into the host genome. Transduction: a bacteriophage injects DNA into the cell that contains a small fragment of DNA from a different prokaryote. Conjugation: DNA is transferred from one cell to another via a pilus that connects the two cells (most common form). Prokaryotic Metabolism Macronutrients: CHNOPS Carbon: major element in all macromolecules Hydrogen and Oxygen: organic compounds and water Nitrogen: proteins and nucleic acids Phosphorus: synthesis of nucleotides and phospholipids Sulfur: some amino acids, vitamins, and coenzymes Micronutrients: metallic elements Iron Boron Manganese Metabolic Diversity of Prokaryotes Energy source ○ Phototrophs: sunlight ○ Chemotrophs: chemical compounds Chemoorganotrophs (organic) Chemolithotrophs (inorganic) Carbon source ○ Autotrophs: inorganic compounds such as CO2 ○ Heterotrophs: organic compounds Photoautotrophs: sunlight + CO2 Chemoheterotrophs: energy & carbon from chemical compounds Chemoautotrophs: energy from chemical compounds & carbon from CO2 Photoheterotrophs: light + organic compounds made by other organisms Carbon and Energy Sources Energy Source Electron Source Organic material (organotroph) Light (phototroph) Inorganic material (lithotroph) Organic material (organotroph) Chemicals (chemotroph) Inorganic material (lithotroph) Carbon Source Nutritional Type Organic material (heterotroph) Photoorganoheterotroph Carbon dioxide (autotroph) Organic material (heterotroph) Carbon dioxide (autotroph) Photolithoautotroph Organic material (heterotroph) Chemoorganoheterotroph Carbon dioxide (autotroph) Organic material (heterotroph) Chemolithoheterotroph Carbon dioxide (autotroph) Chemolithoautotroph Diversity of Oxygen Requirements in Prokaryotes Obligate aerobes: require oxygen for ATP production via cellular respiration Obligate anaerobes: oxygen is toxic; use fermentation or anaerobic respiration with inorganic molecules like SO4, NO3 ○ Gut bacteria Facultative anaerobes: can produce ATP with or without (fermentation) oxygen Prokaryotes: Bacteria and Archaea Prokaryote is not a taxonomic term (anymore) Bacteria and Archaea are both prokaryotes but differ enough to be placed in separate domains. An ancestor of modern Archaea is believed to have given rise to Eukarya, the third domain of life. Bacteria vs. Archaea Plasma membrane 1. Archaea: branched with ether bonds 2. Bacteria: unbranched with an ester linkage Bacteria vs. Archaea Cell wall Bacteria: composed of peptidoglycan Archaea: composed of polysaccharides Gene expression Archaeal transcription and translation are more similar to those of eukaryotes Enzymes are similar Pathogenicity Archaea: none are pathogenic to humans Classification of Bacteria Generally, most species of bacteria are divided into two major groups: Gram positive and Gram negative. Both groups have a cell wall composed of peptidoglycan: in Gram-positive bacteria, the wall is thick, whereas in Gram-negative bacteria, the wall is thin. Domain Bacteria 1. Proteobacteria: gram-negative; eukaryotic mitochondria are thought to be derived from this group 2. Chlamydias: obligate intracellular parasites of animal cells; cell walls lack peptidoglycan 3. Spirochetes: spiral-shaped cells; mostly anaerobic 4. Cyanobacteria: photosynthetic; eukaryotic chloroplasts are thought to be derived from this group 5. Gram-positive bacteria: thick cell wall Domain Archaea 1. Euryarchaeota: methanogens & halobacteria 2. Crenarchaeota: carbon fixation & sulfur-dependent/ thermophilic/ hyperthermophilic extremophiles 3. Nanoarchaeota: 1 species that is an obligate symbiont with another species of archaea; found in hydrothermal vents in Yellowstone NP & deep sea vents 4. Korarchaeota: primitive; found in only one hot spring in Yellowstone NP Roles of Prokaryotes in Ecosystems Present and abundant in every ecosystem in the world Carbon cycle Producers: photosynthetic bacteria Consumers: use organic compounds from producers and release CO2 to atmosphere Decomposers: make organic molecules from dead organisms available Roles of Prokaryotes in Ecosystems Nitrogen cycle: Nitrogen in the atmosphere (N2) is not usable by plants Nitrogen fixation: N2 to NH3 (ammonia) Ammonification: released during decomposition Nitrification: ammonia converted to nitrate Figure 22.19 The nitrogen cycle. Prokaryotes play a key role in the nitrogen cycle. (credit: Environmental Protection Agency) Human Bacterial Disease In the early 20th century, infectious diseases killed 20% of children before the age of five Sanitation and antibiotics → higher survival rates In recent years, however, many bacterial diseases have appeared and reappeared Bacteria resistant to antibiotics Biofilms and Disease Microbial community that are difficult to destroy Foodborne diseases Legionnaires’ disease Otis media (ear infection) Dental plaque Medical devices → causes 65% of infections acquired in hospitals Resistant to drugs Examples of Human Impact by Bacteria Dental caries (tooth decay) Plaque consists of bacterial biofilms Streptococcus sobrinus ferments sugar to lactic acid Tooth enamel degenerates Peptic ulcers Helicobacter pylori is the main cause Treated with antibiotics Tuberculosis Mycobacterium tuberculosis Problem for thousands of years Afflicts the respiratory system Easily transferred from person to person through the air Multidrug-resistant (MDR) strains are becoming more common E. coli (a) Vegetable sprouts grown at an organic farm were the cause of an (b) E. coli outbreak that killed 32 people and sickened 3,800 in Germany in 2011. The strain responsible, E. coli O104:H4, produces Shiga toxin, a substance that inhibits protein synthesis in the host cell. The toxin (c) destroys red blood cells resulting in bloody diarrhea. Deformed red blood cells clog the capillaries of the kidney, which can lead to kidney failure, as happened to 845 patients in the 2011 outbreak. Kidney failure is usually reversible, but some patients experience kidney problems years later. Black Death The (a) Great Plague of London killed an estimated 200,000 people, or about twenty percent of the city’s population. The causative agent, the (b) bacterium Yersinia pestis, is a Gram-negative, rod-shaped bacterium from the class Gamma Proteobacteria. The disease is transmitted through the bite of an infected flea, which is carried on a rodent. Symptoms include swollen lymph nodes, fever, seizure, vomiting of blood, and (c) gangrene. Lyme Disease Lyme disease usually results in (a) a characteristic bullseye rash. The disease is caused by a (b) Gram-negative spirochete bacterium of the genus Borellia. The bacteria (c) infect ticks, which in turns infect mice. Deer are the preferred secondary host, but the ticks also may feed on humans. Untreated, the disease causes chronic disorders in the nervous system, eyes, joints, and heart. The disease is not new, however. Genetic evidence suggests that Ötzi the Iceman, a 5,300-year-old mummy found in the Alps, was infected with Borellia. Pathways of Infection Natural reservoir: the population of organisms which harbors a pathogen and transmits it to the target population ○ ○ Reservoir species typically do not experience symptoms of the disease Bats, rats, cows, etc. Vector species: an organism that transmits a pathogen to another organism ○ Mosquitos, ticks, fleas, etc. Eradication of diseases ○ ○ Smallpox (1980): vaccination and no natural reservoir Rinderpest (2010): vaccination Antibiotics and Superbugs Antibiotics: chemicals produced by microbes or synthetically that prevents the growth of other organisms Ex: penicillin is produced by fungi to stop the growth of bacteria Antibiotic resistance is caused by overuse and misuse of antibiotics ○ ○ Livestock: 70% of antibiotics produced are fed to animals Viral infections MRSA Methicillin-resistant Staphylococcus aureus Resistant to many antibiotics Common in healthcare facilities ○ Mean age = 68 Tight populations ○ Mean age = 23 Figure 22.25 MRSA. This scanning electron micrograph shows methicillin-resistant Staphylococcus aureus bacteria, commonly known as MRSA. S. aureus is not always pathogenic, but can cause diseases such as food poisoning and skin and respiratory infections. Beneficial Prokaryotes Only a small percentage are pathogenic Bacteria are vital to the environment Decomposers release a dead organism’s atoms to the environment Food production: bread, wine, cheese Fixation Photosynthesizers fix carbon into sugars ○ Ancient cyanobacteria added oxygen to air Biological nitrogen fixation Cyanobacteria in aquatic environments Symbiotic nitrogen fixation: sustainable agriculture Beneficial Prokaryotes Microbial bioremediation A. Cleaning up oil after the Valdez spill in Alaska, workers hosed oil from beaches and then used a floating boom to corral the oil, which was finally skimmed from the water surface. Some species of bacteria are able to solubilize and degrade the oil. B. One of the most catastrophic consequences of oil spills is the damage to fauna. Beneficial Prokaryotes Human microbiome ○ ○ ○ ○ ○ Food digestion Protection from pathogens Produce vitamins Gut microbes can influence our mood, energy level, weight control Allergies & autoimmune diseases Example: Clostridium difficile Part of normal gut biome Suppressed by other microbes Antibiotics disrupt normal levels C. diff becomes infectious Mouth: 100 – 200 species Your microbial fauna Equal number of human and bacterial cells in your body Skin: Up to 1000 species Gut: Up to 1000 species Lungs: 128 species Virus Hunter Activity video: 9 minutes