How Do Bacteria Reproduce?

2. How Do Bacteria Reproduce? • Not Mitosis • Not Meiosis • No Spindle Fibers Formed • Prokaryotes Reproduce By Binary Fission

3. How Do Prokaryotes Reproduce? • The cell doubles in mass • DNA replicates and the two strands separate • Cytokinesis is an inward pinching of the cell membrane and cell wall to separate the cell into two genetically identical cells Figure 5.2a, page 139

4. E. Coli Growth Rate ~5 hours growth condensed into 7 seconds

5. Prokaryotes Reproduce Asexually • The generation time is the interval of time between successive binary fissions • Asexual reproduction = no difference between cells (a generalization which we will clarify later) • In pathogens, a shorter generation time means a shorter incubation period of disease Figure 5.3, page 140

6. Population Growth Curve Figure 5.4, page 142

7. Prokaryotic Growth • A Bacterial Growth Curve Illustrates the Dynamics of Growth • During the lag phase, no cell division occurs while bacteria adapt to their new environment • Exponential growth of the population occurs during the logarithmic (log) phase • Human disease symptoms usually develop during the log phase • When reproduction rate = death rate, the population enters the stationary phase • The accumulation of waste products and scarcity of resources causes the population to enter the decline (exponential death) phase

8. Endospores Are a Response to an Environmental Limitation • Endospores are a highly resistant structure formed by species of Bacillus and Clostridium when nutrient supplies are low • Endospores often begin to form at the beginning of the decline phase Figure 5.6, page 144

9. A stressed cell undergoes asymmetrical cell division, creating a small prespore and larger mother cell • The prespore contains: • Cytoplasm • DNA • dipicolinic acid, which stabilizes proteins and DNA • The mother cell matures the prespore into an endospore, then disintegrates, freeing the spore • Endospores: • are resistant to desiccation, heat, alcohol • undergo very few chemical reactions

10. Vegetative and Sporulation Cycle Vegetative Cycle

11. When environmental conditions are again favorable, protective layers break down and the spore germinates into a vegetative cell Figure 5.6c, page 144

12. Spore-forming Bacteria That Cause Serious Diseases Include: • Bacillus anthracis – Anthrax • Bacillus cereus – Bacillus cereus food poisoning • Clostridium botulinum – Botulism • Clostridium perfringens – Gas Gangrene • Clostridium tetani - Tetanus

13. Remember that sporulation is not cell reproduction; It is cell replacement

14. Environmental Factors that Affect Prokaryotic Growth • Temperature • Gasses • pH • Hydrostatic Pressure • Salt

15. Environmental Factors that Affect Prokaryotic Growth • Temperature • Each prokaryotic species has an optimal temperature for growth and about a 30° range of acceptable temperatures

16. Psychrophiles • grow optimally below 15°C, and make up the largest portion of all prokaryotes on Earth

17. Psychrotrophs - cold tolerant • Psychrotrophs do not favor cold conditions, but can tolerate them

18. Mesophiles ~10-40o C • Thrive at the medium temperature range of 10° to 45°C, including pathogens that thrive in the human body

19. Thermophiles • Multiply best around 60°C, living in compost heaps and hot springs

20. Hyperthermophiles • Are Archaea that grow optimally above 80°C, found in seafloor hot-water vents

21. Figure 5.8, page 147

22. Gasses • Oxygen • Many prokaryotes are obligate aerobes, which require oxygen to grow • Anaerobes do not or cannot use oxygen; aerotolerant species are insensitive to oxygen, but obligate anaerobes are inhibited or killed by oxygen • Facultative prokaryotes grow either with oxygen, or in reduced oxygen environments

23. Gasses, cont: • Microaerophiles require <21% atmospheric oxygen • Thioglycollate broth can be used to test an organism’s oxygen sensitivity • Carbon Dioxide • Capnophiles require an atmosphere low in oxygen and rich in carbon dioxide

24. Capnophiles can be grown in the lab in candle jars and “gas pak” containers

25. Microbial Mat

26. pH • The majority of species grow optimally at neutral (~7.0) pH • The pH of human body fluids is ???? • Therefore …. • Acidophiles are acid-tolerant prokaryotes • For example, those used to turn milk into buttermilk, sour cream, and yogurt • Alkalophiles tolerate basic environments • For example, soda lakes

27. Hydrostatic Pressure • Barophiles can tolerate high amounts of pressure • e.g., psychrophiles that live at the bottom of the ocean

28. Salt • Halophiles can tolerate high amounts of salt

29. Culture Media = What Microbes Are Grown On Or In • Supply required nutrients to maintain culture • 2 basic types: • General purpose media • Enriched media

30. General Purpose Medium– Will Grow Most Bacteria • We usually start with these: • Nutrient Broth = Meat broth + Peptone • Add agar = Nutrient Agar OR • Tryptic Soy Broth – Soy protein + Tryptone • Add agar = Tryptic Soy Agar

31. Some Bacteria Can Not Grow On General Purpose Media • Have Specific Nutrient Requirements – Enriched Media • “picky eaters” = “Fastidious” • Examples: • Blood Agar • Chocolate Agar

32. Some Media Aid in the Identification of Prokaryotes • Selective Media– Inhibits the Growth of Certain Species and Facilitates the Growth of Others (Bacillus anthracis On a Selective Medium)

33. Differential Media • Differentiates Between Species By Employing Chemical Indicators • Usually Cause a Color Change

34. Compare Differential and Selective Media….

35. Streak Plate Technique is Used to Isolate and Identify Species – What Does the Patient Have? • There are many streak plate techniques • They are all a form of serial dilution of the specimen

36. Quantification Techniques Can Be Used To Quantify Bacteria – How Sick Is the Patient? • Pour Plate Technique

37. Population Growth Can Be Measured in Several Other Ways • Coulter Counter • Turbidity can be measured using a spectrophotometer • Direct count using a counting chamber

38. Coulter Counter

39. A Direct Microscopic Count Figure 5.13, page 157

40. Other Terms: • Pure Culture= Only one species of bacteria, and you know what it is • Mixed Culture= More than one species of bacteria, and you know what they are • ? What is a Culture called when you don’t know what it is?

41. Other Terms, cont: • Natural Medium– uses all natural ingredients • Ex: Blood agar plate • Synthetic Medium– Is made in the lab using chemicals (shown is synthetic sea fog)