Chapter 19-1 - Prokaryotes

1. Chapter 19-1 - Prokaryotes

2. New Technology Leads to New Discovery • The invention of the microscope allowed humans to see things never before seen • The work of Hooke and van Leeuwenhoek opened our eyes to the world of microorganisms

3. Prokaryotes • Prokaryote – a single-celled organism that lacks a nucleus (“pro” = before, “karyote” = nucleus) • Prokaryotes are typically referred to as bacteria • Prokaryotes are the smallest & most common microorganisms • Prokaryotes cover nearly ever centimeter of the earth • Prokaryotes are the oldest and most successful organisms on the planet

4. Prokaryotic Cell Structure • A typical prokaryotic cell has a cell wall, cell membrane, cytoplasm, DNA, ribosomes, flagella, and pili • Flagella (pl. flagellum) – a whip-like structure used for movement • Pili – projections on the outer part of the cell involved in cell to cell contact • DNA – bacteria have a single, circular chromosome and small circles of DNA called plasmids • Capsule – an outer covering that helps protect the bacteria cell • Bacteria have no membrane-bound organelles (nucleus, mitochondria, etc.)

5. Classifying Prokaryotes • There are 2 kingdoms of bacteria: • Eubacteria • “true bacteria” • Well adapted to most current earth habitats\ • The bacteria we refer to as “germs” are eubacteria • Archaebacteria • “ancient bacteria” • Well adapted to extreme habitats, some of which may closely resemble the ancient earth (~3bya)

6. Eubacteria: A closer look • Most prokaryotes are eubacteria • The kingdom eubacteria includes a wide range of bacteria with varying habitats and lifestyles • The cell walls of eubacteria are composed of a carbohydrate called peptidoglycan • Eubacteria are found all around, on, and in us, all the time, wherever we go!

7. Archaebacteria: A closer look • Archaebacteria are similar in structure to eubacteria, yet have a few key differences: • No peptidoglycan in cell wall • Different membrane lipids • Live in extreme environments (high salt, high heat, etc.)

8. An ancestor to eukaryotes? • Certain important archaebacteria genes (EX. RNA polymerase gene) are more similar to eukaryotic genes than to eubacterial genes • Scientists now believe this is evidence that eukaryotes evolved from archaebacteria, and are not directly descended from the more common eubacteria

9. Types of Archaebacteria • Methanogens – Live in environments with no oxygen (mud pits, landfills, intestinal tracts) and get energy by converting H2 and CO2 into CH4 (methane) • Extreme Halophiles – Live in high salt environments, use salt to generate ATP • Thermoacidophiles – Live in acidic and/or high temperature environments (hydrothermal vents, volcanoes, hot springs) and get energy by breaking down sulfur compounds

10. Identifying Prokaryotes • Shapes – Prokaryotes usually have one of three shapes: • Bacilli (bacillus) – rod-shaped bacteria • Cocci (coccus) – spherical bacteria • Spirilla (spirillum) – spiral-shaped bacteria • Some bacteria-naming prefixes: • Diplo = pairs of cells (EX. Diplobacilli) • Staphylo = clusters of cells (EX. Staphylococcus) • Strepto = chains of cells (EX. Streptococcus)

11. Identifying Prokaryotes • Cell Walls – Eubacteria have 2 different types of cells walls (single or double) • Gram staining is a process used to indicate the cell wall type – two stains, violet and pink, are applied and the bacteria are then observed • Gram-positive bacteria have a a cell wall made of a thick peptidoglycan layer (single wall) and appear purple when stained (both stains absorbed) • Gram-negative bacteria have a cell wall made of a thin peptidoglycan layer and an outer lipid layer (double wall), and appear pink when Gram stained (only pink stain is absorbed)

12. Obtaining Energy • Some bacteria are autotrophs (“self-feeders”) that make their own organic molecules (food) • Photoautotrophs – bacteria that carry out photosynthesis similar to plants • EX. Cyanobacteria contain light absorbing pigments and are found all over the world • Chemoautotrophs – bacteria that make organic molecules using energy from the breakdown of inorganic (no carbon) molecules such as ammonia or sulfur • EX. Bacteria living on or around hydrothermal vents on the ocean floor

13. Obtaining Energy • Some bacteria are heterotrophs (“other-feeders”) that get energy by taking in organic molecules (eating). • Heterotrophic bacteria compete with humans for food (food “spoilage” is due to bacteria) • Many heterotrophic bacteria secrete toxic chemicals to prevent other organisms from stealing their food • EX. Salmonella bacteria secrete a toxic substance that causes food poisoning

14. Obtaining Energy • Some bacteria are photoheterotrophs that capture sunlight for energy and consume organic molecules

15. Carrying Out Respiration • Bacteria get energy by breaking down molecules during the process of respiration and/or fermentation • Obligate aerobes (aerobic bacteria) require oxygen and depend mainly on respiration for energy • The necessary proteins for respiration are found in the cell membrane (bacteria have no mitochondria)

16. Carrying Out Respiration • Obligate anaerobes (anaerobic bacteria) do not require oxygen and cannot survive in oxygen-rich environments • Fermentation only • EX. Clostridium tetani, Clostridium botulinum • Facultative anaerobes can survive with or without oxygen • Able to switch between respiration and fermentation • Can survive just about anywhere

17. Growth and Reproduction • In favorable conditions, prokaryotes can grow and divide quickly • A single prokaryotic organism with unlimited resources, dividing every 20 minutes, would produce a mass of bacteria 4000X the mass of the earth in 48 hours • This doesn’t happen due to lack of resources and the production of waste

18. Growth and Reproduction • Bacteria reproduce by binary fission • Cell grows until double in size • DNA is replicated • Cell splits in half producing identical daughter cells • Binary fission is asexual reproduction, it does not involve the exchange or recombination of genetic information (all DNA comes from one parent)

19. Growth and Reproduction • Conjugation – process where a DNA plasmid is copied and passed from one bacteria cell to another • Two bacteria are joined by pilus • DNA plasmids move from one cell to the other • This increases the genetic diversity of a bacteria population • Transformation – when bacteria take up pieces of DNA secreted by live bacteria or released by dead bacteria giving them new traits

20. Growth and Reproduction • Some bacteria are able to survive harsh environmental conditions for long periods • Endospore – A thick, internal wall enclosing a bacteria cell’s DNA and a portion of the cytoplasm • Formed when growth conditions are unfavorable • Can remain dormant for months or even hundreds of years • Makes it possible for bacteria to survive harsh conditions (extreme heat, lack of food, etc.)

21. Chapter 19-2 – Bacteria in Nature

22. Bacteria play an essential role in maintaining the ecosystem • Decomposer – organism that breaks down dead organisms/organic material for food • Many bacteria are decomposers • Decomposers break down dead matter into simpler substances which are released to the soil where they can be reused by plants • What would happen without decomposers? • There would be dead stuff piled up everywhere!

23. Bacteria play an essential role in maintaining the ecosystem • Nitrogen Fixation – The process of converting atmospheric nitrogen gas (N2) to ammonia (NH3) or other nitrogen compounds that plants can use • Plants need nitrogen to make amino acids which in turn are used to make proteins • Plants cannot use N2 directly • Nitrogen-fixing bacteria provide enrich the soil with nitrogen containing compounds • Animals get their nitrogen from plants (either directly or indirectly)

24. Bacteria and Disease • There are approximately 10X as many bacteria cells in you than human cells • Most are on your skin or somewhere in your digestive system • These bacteria are kept under control by your immune system • A few are actually beneficial • Aid in digestion • Produce necessary vitamins • Compete for living space with potentially harmful bacteria

25. Escherichia coli in the human intestines • E. coli normally colonizes an infant's intestines within 40 hours of birth, arriving with food or water or with the individuals handling the child • Harmless strains of E. coli benefit the host by producing vitamin K (necessary for blood coagulation) • They also prevent harmful bacteria from becoming established in the intestine

26. Bacteria and Disease • A few types of bacteria cause disease (pathogenic bacteria) • Pathogen – a disease-causing agent, like some bacteria • Bacteria cause disease in one of two general ways: • Damaging tissues of host organism by breaking them down for food • EX. Tuberculosis bacteria break down lung tissue • Releasing toxins that harm the body • EX. Tetanus is caused by a neurotoxin produced by Clostridium tetani bacteria

27. Bacterial Diseases • Tetanus • Typhoid Fever • Diptheria • Syphilis • Cholera • Food poisoning • Leprosy • Tuberculosis • Meningitis

28. Bacteria and Disease • Many bacterial diseases can be prevented • Vaccines stimulate the body’s immune system and prevent bacteria from colonizing body tissues • Antibiotics – compounds that block the growth or reproduction of bacteria • Penicillin, the first antibiotic, was developed in 1942 • For the first time, humans had a way to treat bacterial infections (short of sawing off appendages!) • Good personal/environmental hygiene help prevent bacterial infections from spreading (hand washing, sewage system, etc.) • Major reason for increased life expectancy = increased knowledge of preventing and treating bacterial diseases

29. The discovery of antibiotics • 1928 -Alexander Fleming investigates staphylococci. • August 1928 - Fleming goes on vacation, leaves all his cultures of staphylococci on a bench in the lab • On returning, Fleming notices that one that the colonies of staphylococci culture was contaminated with a fungus, and bacteria that had immediately surrounded it had been destroyed • The fungus was from a group of fungi called Penicillum, and he called the bacteria-killing substance it produced penicillin

30. Discovery of Penicillin

31. Antibiotic Resistance – Too much of a good thing? • Many bacteria have developed resistance to certain antibiotics • The more we use antibiotics, the more we risk the development of resistant bacteria strains • Antibiotics are frequently prescribed unnecessarily, and taken irresponsibly • Antibiotics are used extensively in agriculture • In some cases, bacteria can be resistant to more than one type of antibiotic • Resistance is determined by genes, and can be transferred from one bacteria to another via transformation or transduction • Antibiotic resistance poses a significant problem for human health now and in the future

32. Controlling Bacteria • Sterilization – destroying bacteria with either heat or chemicals • Cooking food kills most bacteria • Disinfectant – a chemical solution that kills bacteria • Refrigeration/freezing prevents food spoilage • Bacteria grow more slowly at low temperatures • Different preservation techniques can be used to store food for long periods • Canning – sealing sterilized food in cans or glass jars • Salting – draws moisture out of food/bacteria cells • Pickling – vinegar is highly acidic and prevents most bacterial growth

33. Canning Tomatoes250 lbs of tomatoes + 10-12 hours = 45 to 50 quarts of crushed tomatoes

34. Human Uses of Bacteria • Bacteria are used in the production of a variety of foods • Cheeses, buttermilk, yogurt, sour cream, pickles, sauerkraut, vinegar • Bacteria are used in industry • Water treatment, oil spill clean up, botox • Insulin is produced using bioengineered bacteria, as is human growth hormone, antibiotics, and other chemicals