Chapter 27: Bacteria and Archaea What are they? 2 Domains: Bacteria and Archea Both domains include only prokaryotes. mostly unicellular species that are about 10 times smaller than eukaryote cells. Lack membrane enclosed organelles-including a nucleus. They are almost everywhere! Great evolutionary success and large diversity Found in hot springs and 2 miles below the Earth?s surface, found on your desktop and in your body. Why are they so successful? A wealth of evolutionary adaptations Structural Functional Genetic Nutritional and metabolic advantages Symbiotic What allows for all the adaptations? Reproduction Asexual by binary fission 1 --> 2--> 4 Does not require 2 parent cells! Rapid- many divide every 1-3 hours some every 20 minutes Transformation The uptake of genetic material from the surroundings Does not require a ___________ _____________ The genotype is altered The phenotype may be altered Conjugation The transfer of genetic material between 2 bacterial cells The cells do not need to be from the same species Not sexual reproduction One way F-Factor DNA - the DNA that is transferred Sex pili - the required structure Plasmids Small rings of DNA that have only a few genes. Provide resistance to antibiotics. Enable metabolism of rarely found nutrients. Increase the chance of survival in unusual circumstances. Transduction The transfer of genetic information from one bacterium to another by a bacteriophage A horizontal gene transfer Bacterial DNA from the infected host is inadvertently packaged into the virus subsequently transferred Basic Prokaryote Structure Shapes are variable, but 3 are most common Coccus (cocci)- spherical Bacillus (bacilli)- rod shaped Spiral Fig 27.2 p. 557 Prokaryotic Cell Walls Maintains shape, provides physical protection Prevents lysis in a hypotonic environment In a hypertonic environment cells shrink away from their cell walls (plasmolyze) Inhibits reproduction Salt used as a preservative Bacterial walls: peptidoglycan- carbohydrates crosslinked by polypeptides ________ : eukaryotes with cell walls have chitin or cellulose in them Archean walls: Similar sugar/ polypeptides but not peptidoglycan Two types of bacteria based on cell wall composition Detected using the Gram Stain Gram (+) - large amounts of peptidoglycan Gram (-) -less peptidoglycan, in between plasma membrane and a second, outer membrane containing lipopolysaccharides The Gram Stain Hans Christian Gram, 1800?s Very useful even today Gram (-)s are generally more virulent and resistant to more antibiotics than gram positives. The Procedure The specimen is stained with a crystal violet dye fixed with iodine washed in alcohol and counter stained with a red dye. Positive=violet negative=red Fig 27.3 p 557 Cell Wall Associated structures Capsule-optional sticky layer that coats the surface Usually composed of sugars Contributes to pathogenicity- ability to evade immune systems 2. Appendages fimbriae: numerous, for adhesion Sex pili: longer than fimbriae and not as numerous Link cells during conjugation Prokaryotic Motility 1/2 of prokaryotes have directional movement Flgella - most common means Smaller and simpler than eukaryotic flagella A proton pump powers a basal apparatus to turn a hook which is attached to long chains of the protein flagellin Taxis- movement toward or away from a stimulus Fig 27.6 p 558 prokaryotic flagellum Fig 6.24 p 115 Eukaryotic Flagella What?s in the cytoplasm? No compartmentalization Nucleoid region - location of DNA Many similarities- proteins are different from eukaryotic ribosome proteins Specialized membrane systems Originate in plasma membrane Ex: respiratory membranes: function like mitochondrial membranes Fig 27.7 p 559 Fig 27.7 p 537 Endospores structural adaptation seen in some species. Form in harsh environments A copy of the chromosome is surrounded by a tough wall. Water is expelled, metabolism stops Remainder of cell disintegrates Can survive boiling To destroy - must be heated to 121o under pressure Special equipment- Autoclave Fig 27.9 p. 560 Anthrax Nutritional Adaptations 1. Photoautotrophs- use light to produce organic molecules from CO2. Plants and algae too! Cyanobacteria 2. Photoheterotrophs- Use light energy, convert carbon nutrients to different organic nutrients Marine bacteria 3. Chemoautotroph- use inorganic compounds as a source of energy to convert CO2 to organic molecules- unique to prokaryotes! Sulfolobus 4. Chemoheterotrophs- consume organic molecules for energy and for a carbon source. Very common- we are in this category. See table 27.1 p 564 Oxygen metabolism Obligate aerobes- require O2 Respiration Facultative aerobes- survive without the presence O2 Respiration or anaerobic Obligate anaerobes- poisoned by O2 Fermentation or respiration with a different chemical energy (Ex. SO4-2) Nitrogen metabolism Some prokaryotes can convert atmospheric nitrogen (N2) to ammonia (NH3) Nitrogen Fixation Eukaryotes cannot utilize N2 Beneficial to all life- Metabolic Cooperation Among different species survival in limiting environments Ex: Biofilms - surface coating multi-species colonies Bond to form a matrix to which future cells adhere Send signals to recruit nearby bacteria Channels allow passage of nutrients and wastes Impact of Biofilms Contribute to tooth decay Damage industrial and medical equipment Prokaryotic phylogeny Genetic diversity is immense Horizontal gene transfer: a large role in evolution. Acquiring genes from distantly related species Bacteria and Archea diverged very early. Archea are more similar to eukaryotes than to Bacteria. Archea Many unique characteristics Ex: Extremophiles - live in extreme environments Heat (thermophiles) high salt (halophiles) Methanogens-anaerobes that use CO2 to oxidize H2 Methane gas is the waste- ?marsh gas? Decompose sewage, aid digestion in some animals Harmful Impact on Humans Half of all human diseases caused by prokaryotes 2 million die of lung diseases caused by prokaryotes every year 2-3 million people die every year of diarrheal diseases Most bacterial disease is caused by the production of toxins TB (Tuberculosis) The leading cause of death in the world from bacterial infectious disease. Affects 1.7 billion people/year (CDC) 1/3 of the world?s population Initial infection is walled off in the lungs by the immune system ____________ years later to cause active TB A slowly progressive disease Fig 27.16 A spirochete transmitted by a tick causes lyme disease Toxins Exotoxins- secreted proteins Ex. The exotoxin produced by Vibrio cholera causes cholera. Endotoxins - Components of the outer membrane of Gram negative bacteria Released when a cell dies Ex. Salmonella a species all have endotoxins Other Harmful Impacts Horizontal gene transfer can turn harmless species into fatal pathogens E. coli ordinarily harmless, pathogenic strains have emerged Due to acquisition of DNA encoding toxins Bioterrorism 2001, B. anthracis in envelopes mailed to government leaders and news media members Other organisms are prime candidates Prokaryotes in Research and Technology Bacteria convert milk to cheese and yogurt E. coli used in cloning genes Bioremediation- using bacteria to remove pollutants Decompose sewage to make fertilizer Cleaning up oil spills
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