Microbial Metabolism

1. Microbial Metabolism Unit 2: 7 days

2. February 3rd and 4th: Microbial Metabolism • The sum of all chemical reactions in a living organism is called metabolism

3. Microbial Metabolism • Catabolism refers to chemical reactions that result in the breakdown of more complex organic molecules into smaller substances • Catabolic reactions usually release energy

4. Microbial Metabolism • Anabolism refers to chemical reactions in which simpler substances are combined to form more complex molecules • These reactions usually require energy

5. Microbial Metabolism • The energy of catabolic reactions is used to drive anabolic reactions • The energy for chemical reactions is stored in ATP

6. Enzymes • Proteins produced by living cells, that catalyze chemical reactions by lowering the activation energy • Generally globular proteins with characteristic shapes

7. Naming Enzymes • Usually end in – ase • Six different classes, defined based on the type of reactions they catalyze

8. Energy Production • Oxidation-reduction reaction • LEO • GER • When one substance is oxidized, another is reduced • NAD+ is the oxidized form, NADH is the reduced form

9. Energy Production • Glucose is a reduced molecule • Energy is released during a cell’s oxidation of glucose

10. Energy Production • Energy release can be trapped to form ATP from ADP and phosphate • Addition of a phosphate is called phosphorylation

11. Energy Production • A series of enzymatically catalyzed chemical reactions called metabolic pathways store energy in and release energy from organic molecules

12. Carbohydrate Catabolism • Most of a cell’s energy is produced from the oxidation of carbohydrates • Glucose is the most commonly used carb • There are two major pathways of glucose catabolism: • Respiration • Completely broken down • Fermentation • Partially broken down

13. Review

14. Alternatives to Glycolysis • The pentose phosphate pathway is used to metabolize 5 carbon sugars • Operates simultaneously with glycolysis • The Entner-Doudoroff pathway • Requires special enzymes • Found in some gram-negative bacteria • Both yield one ATP and two NADPH molecules are produced from one glucose

15. Cellular Respiration Review • Organic molecules are oxidized • Energy is generated from the ETC • In aerobic respiration, O2 is the final electron acceptor • In anaerobic respiration, a different inorganic molecule is the final electron acceptor

16. Aerobic Respiration Review • The Krebs Cycle:

17. Aerobic Respiration Review • The Electron Transport Chain:

18. Aerobic Respiration Review • The mechanism of ATP synthesis using the ETC is called chemiosmosis • Protons being pumped across the membrane produce force caused by electrons moving along the chain • The protons then move back across the membrane, and ADP is turned into ATP by the protein ATP synthase • In eukaryotes the electron carriers are located in the inner mitochondrial membrane • In prokaryotes they are in the plasma membrane

19. Aerobic Respiration Summary • In aerobic prokaryotes 38 ATP molecules can be produced from complete oxidation of a glucose molecule • In eukaryotes 36 ATP molecules can be produced from complete oxidation of a glucose molecule

20. Anaerobic Respiration Review • The final electron acceptors can be nitrate, sulfate, or carbonate • The total ATP yield is less than aerobic respiration because only part of the Krebs cycle is operating

21. Fermentation Review • Releases energy from molecules through oxidation • Oxygen gas is not required • Two ATP molecules are produced • Electrons removed from the substrate reduce NAD+ • The final electron acceptor is an organic molecule

22. Fermentation Review • In lactic acid fermentation, pyruvic acid is reduced by NADH to lactic acid • In alcohol fermentation, acetaldehyde is reduced by NADH to produce ethanol • Heterolactic fermenters can use the pentose pathway to produce lactic acid and ethanol

23. Photosynthesis Review • Conversion of light energy from the Sun into chemical energy • This chemical energy is then used for carbon fixation

24. Photosynthesis Review

25. Metabolic Diversity • Photoautotrophs obtain energy through photophosphorylation and fix carbon from CO2 using the Calvin cycle to synthesize organic molecules • Cyanobacteria are oxygenic phototrophs • Green and purple sulfur bacteria are anoxygenicphototrophs

26. Cyanobacteria

27. Purple Sulfur Bacteria

28. Metabolic Diversity • Photoheterotrophs use light as an energy source and an organic molecule for their carbon source or electron donor • Chemoautotrophs use inorganic compounds as their energy source and CO2 as their carbon source

29. Metabolic Diversity • Chemoheterotrophs use complex organic molecules as their carbon and energy sources

31. February 6th: Microbial Growth • The growth of a population is an increase in the number of cells or in mass • Microbes have both physical and chemical requirements for growth

32. Physical Requirements • Temperature: • Psychrophiles (cold-loving) • Mesophiles (moderate-loving) • Thermophiles (heat-loving)

33. Psychrophiles at Everest Base Camp

34. Physical Requirements • Minimum growth temperature = the lowest temperature at which a species will grow • Optimum growth temperature = the temperature at which a microbe grows the best • Maximum growth temperature = the highest temperature at which growth is possible

35. Physical Requirements • Most bacteria grow best at a pH value between 6.5 and 7.5 • In a hypertonic solution most microbes undergo plasmolysis • Halophiles can tolerate high salt concentrations

37. Chemical Requirements • Carbon source • Nitrogen source • Needed for nucleic acid and protein synthesis • Can be obtained: • From the decomposition of proteins • From nitrate or ammonium • Some bacteria are capable of nitrogen fixation (N2)

38. Chemical Requirements • Oxygen: • Obligate aerobes • Facultative anaerobes • Obligate anaerobes • Aerotolerant anaerobes • Microaerophiles • Other chemicals: • S, P, trace elements

39. Culture Media • Any material prepared for the growth of bacteria in a laboratory • Microbes that grow and multiply in or on a culture medium are known as a culture • Agar is a common solidifying agent for a culture medium

41. Culture Media • A chemically defined medium is one in which the exact chemical composition is known • A complex medium is one in which the exact chemical composition is not known • Selective media allows for growth of only the desired organism by inhibiting others with salts, dyes, or other chemicals

42. Selective Media

43. Culture Media • Differential media are used to distinguish between different organisms • An enrichment culture is used to encourage the growth of a particular microbe in a mixed culture

44. Culture Media • The normal reproductive method for bacteria is binary fission • One cell splits into two • Some bacteria can reproduce by budding, aerial spore formation, or fragmentation

45. Culture Media • Generation time is the time required for a cell to divide • This is also the time required for a population to double

46. Phases of Growth • During the lag phase the metabolic activity of cells is high, but there is no change in the overall number of cells • During the log phase the bacteria multiply at the fastest rate allowable by environmental conditions

47. Phases of Growth • During the stationary phase equilibrium between cell division and death exists • During the death phase cell death outpaces cell replication

48. Phases of Growth

49. Measuring Growth • A standard plate count reflects the number of viable microbes and assumes that each bacteria grows into a single colony • This can be done using a pour plate or by a spread plate

50. Measuring Growth • A direct count can be done using a microscope and specialized slides • In filtration, bacteria are retained on a membrane and then transferred to a plate to grow and be counted • The most probably number is a statistical estimation using bacteria growing in a liquid medium