Chapter 6 Microbial Growth and Metabolism

1. Chapter 6Microbial Growth and Metabolism • Microbial Nutrition • Microbial Growth • Metabolism

2. 6 – 1.Microbial Nutrition Outline: • Nutrient requirements • Nutritional types of microorganisms • Uptake of Nutrients by the Cell • Culture Medium • Isolation of Pure Cultures

3. Nutrient requirements Concepts: Microorganisms require about ten elements in large quantities, because they are used to construct carbohydrates, lipids, proteins, and nucleic acids. Several other elements are needed in very small amounts and are parts of enzymes and cofactors.

4. Macronutrients • 95% or more of cell dry weight is made up of a few major elements: carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium and iron. • The first six ( C, H, O, N, P and S) are components of carbonhadrates, lipids, proteins and nucleic acids

5. Trace Elements Microbes require very small amounts of other mineral elements, such as iron, copper, molybdenum, and zinc; these are referred to as trace elements. Most are essential for activity of certain enzymes, usually as cofactors.

6. Growth Factors (1)amino acids, (2) purines and pyrimidines, (3) vitamins Amino acids are needed for protein synthesis, purines and pyrimidines for nucleic acid synthesis. Vitamins are small organic molecules that usually make up all or part enzyme cofactors, and only very small amounts are required for growth.

7. Nutritional types of microorganisms

8. Photoautotroph: Algae, Cyanobacteria CO2 + H2O Light+ Chlorophyll（CH2O） +O2 Purple and green bacteria CO2 + 2H2S Light+ bacteriochlorophyll（CH2O） + H2O + 2S Photoheterotroph: Purple nonsulfur bacteria (Rhodospirillum) CO2 + 2CH3CHOHCH3 Light+ bacteriochlorophyll（CH2O） + H2O + 2CH3COCH3

9. Properties of microbial photosynthetic systems

10. Chemoautotroph: Nitrifying bacteria 2 NH4+ + 3 O2 2 NO2- + 2 H2O + 4 H+ + 132 Kcal

11. Culture media are needed to grow microorganisms in the laboratory and to carry out specialized procedures like microbial identification, water and food analysis, and the isolation of particular microorganisms. A wide variety of media is available for these and other purposes.

12. Pure cultures can be obtained through the use of spread plates, streak plates, or pour plates and are required for the careful study of an individual microbial species.

13. Uptake of nutrients Nutrient molecules frequently cannot cross selectively permeable plasma membranes through passive diffusion and must be transported by one of three major mechanisms involving the use of membrane carrier proteins.

14. 1, Phagocytosis–Protozoa 2, Permeability absorption – Most microorganisms • passive transport , simple diffusion • facilitated diffusion • active transport • group translocation

15. passive diffusion A few substances, such as glycerol, can cross the plasma membrane by passive diffusion. Passive diffusion is the process in which molecules move from a region of higher concentration to one of lower concentration as a result of random thermal agitation.

16. Facilitated diffusion The rate of diffusion across selectively permeable membranes is greatly increased by the use of carrier proteins, sometimes called permeases, which are embedded in the plasina membrane. Since the diffusion process is aided by a carrier, it is called facilitated diffusion. The rate of facilitated diffusion increases with the concentratioti gradient much more rapidly and at lower concentrations of the diffusing molecule than that of passive diffusion

17. Active transport Active transport is the transport of solute molecules to higher concentrations, or against a concentration gradient, with the use of metabolic energy input.

18. Group translocation

19. 1, Phagocytosis–Protozoa 2, Permeability absorption – Most microorganisms • passive transport , simple diffusion • facilitated diffusion • active transport • group translocation

20. passive diffusion A few substances, such as glycerol, can cross the plasma membrane by passive diffusion. Passive diffusion is the process in which molecules move from a region of higher concentration to one of lower concentration as a result of random thermal agitation.

21. Facilitated diffusion The rate of diffusion across selectively permeable membranes is greatly increased by the use of carrier proteins, sometimes called permeases, which are embedded in the plasina membrane. Since the diffusion process is aided by a carrier, it is called facilitated diffusion. The rate of facilitated diffusion increases with the concentration gradient much more rapidly and at lower concentrations of the diffusing molecule than that of passive diffusion

22. A model of facilitated diffusion The membrane carrier can change conformation after binding an external molecule and subsequently release the molecule on the cell interior. It then returns to the outward oriented position and is ready to bind another solute molecule. Because there is no energy input, molecules will continue to enter only as long as their concentration is greater on the outside.

23. Active transport Active transport is the transport of solute molecules to higher concentrations, or against a concentration gradient, with the use of metabolic energy input.

24. Group translocation The best-known group translocation system is the phosphoenolpyruvate:sugar phosphotransferase system (PTS), which transports a variety of sugars into procaryotic cells while Simultaneously phosphorylating them using phosphoenolpyruvate (PEP) as the phosphate donor. PEP + sugar (outside) pyruvate + sugar-P (inside)

25. The phosphoenolpyruvate: sugar phosphotransferase system of E. coli. The following components are involved in the system: phosphoenolpyruvate, PEP; enzyme 1, E I; the low molecular weight heat-stable protein, HPr; enzyme 11, E II,- and enzyme III, E III.

26. Simple comparison of transport systems

27. Mode of action of antibacterial antibiotics

28. Symbiosis of peptidoglycan

29. 6 – 2.Microbial growth Outline • The Growth Curve • Cell life cycle • Measurement of Microbial Growth • Measurement of Cell Mass • Growth Yields and the Effects of a Limiting Nutrient • The Continuous Culture of Microorganisms • The Chemostat • The Influence of Environmental Factors on Growth

30. Concepts •   Growth is defined as an increase in cellular constituents and may result in an increase in an organism's size, population number, or both. •  When microorganisms are grown in a closed system, population growth remains exponential for only a few generations and then enters a stationary phase due to factors like nutrient limitation and waste accumulation. If a population is cultured in an open system with continual nutrient addition and waste removal, the exponential phase can be maintained for long periods.

31. 3. A wide variety of techniques can be used to study microbial growth by following changes in the total cell number, the population of viable microorganisms, or the cell mass. 4. Water availability, pH, temperature, oxygen concentration, pressure, radiation, and a number of other environmental factors influence microbial growth. Yet many microorganisms, and particularly bacteria, have managed to adapt and flourish under environmental extremes that would destroy most organisms.

32. Growth definition: Growth may be generally defined as a steady increase in all of the chemical components of an organism. Growth usually results in an increase in the size of a cell and frequently results in cell division

33. Cell life cycle in Eukaryotic cells G1 Primary growth phase of the cell during which cell enlargement occurs, a gap phase separating cell growth from replication of the genome Sphase in which replication of the genome occurs G2Phase in which the cell prepares for separation of the replicated genomes, this phase includes synthesis of microtubules and condensation of DNA to form coherent chromosomes, a gap phase separating chromosome replication from miosis. M phase called miosis during which the microtubular apparatus is associated and subsequently used to pull apart the sister chromosomes. Eukaryotic cell: Prokaryotic cell: G1 S G2 M G1 R D

35. Binary fision Most bacterial cells reproduce asexually by binary fision, a process in which a cell divides to produce two nearly equal-sized progeny cells. Binary fision involves three processes: Increase in cell size (cell elongation), DNA replication Cell division

36. Growth curve of bacteria • Lag Phase • Exponential Phase • Stationary Phase • Death Phase

37. Growth curve of bacteria • Lag Phase • Exponential Phase • Stationary Phase • Death Phase

38. Stationary Phase Logarithmic growth phase Death Phase Lag Phase • (a)Lag phase: cells begin to synthesize inducible enzymes and use stored food reserves. • (b)Logarithmic growth phase: the rate of multiplication is constant. • (c)Stationary phase: death rate is equal to rate of increase. • (d) Death phase: cells begin to die at a more rapid rate than that of reproduction.

39. generation time The time required for a cell to divide (and its population to double) is called the generation time. Suppose that a bacterial population increases from103 cells to 109 cells in 10 hours. Calculate the generation time. Nt = No x 2n G = t log2 / log Nt – log No No = number of bacteria at beginning of time interval. Nt = number of bacteria at end of any interval of time (t). G = generation time T = time , usually expressed in minutes n = number of generation Number of cells Time

40. Continuous culture of microorganisms Chemostat Chemostat used for continuous cultures. Rate of growth can be controlled either by controlling the rate at which new medium enters the growth chamber or by limiting a required growth factor in the medium.

41. Effect of temperature on bacterial growth rate Bacteria grow over a range of temperatures; they do not reproduce below the minimum growth temperattire nor above the maximum growth temperature. Within the temperature growth range there is an optimum growth temperature at which bacterial reproduction is fastest.

42. Enzymes exhibit a Q10 so that within a suitable temperature range the rate of enzyme activity doubles for every 10' C rise in temperature.

43. Microorganisms are classified as psychrophiles, mesophiles.thermophiles, and extremethemophiles based on their optimal growth temperature.

44. Effect of oxygen concentration – reduction potential Effect of oxygen concentration on the growth of various bacteria intubes of solid medium

45. (a) Obligate aerobes-growth occurs only in the short distance to which the oxygen diffuses into the medium. (b) Facultative anaerobes growth is best near the surface, where oxygen is available, but occurs throughout the tube. (c) Obligate anaerobes-oxygen is toxic, and there is no growth near the surface. (d) Aerotolerant anaerobes-growth occurs evenly throughout the tube but is not better at the surface because the organisms do not use oxygen. (e) Microaerophiles, aerobic organisms that do not tolerate atmospheric concentrations of oxygen-growth occurs only in a narrow band of optimal oxygen concentration.

46. Effect of pH value on microbial growth Bacteria: Neutral condition Fungi: Acidic condition Actinomycetes: Alkaline condition

47. Water activity The water activity of a solution is 1/100 the relative humidity of the solution (when expressed as a percent), or it is equivalent to the ratio of the solution's vapor pressure to that of pure water. aw = P solution / P water Approximate lower aw limits for microbial growth: 0.90 – 1.00 for most bacteria, most algae and some fungi as Basidiomycetes,Mucor, Rhizopus. 0.75 for Halobacterium, Aspergillus… 0.60 for some saccharomyces species

48. Plasmolysis If the concentration of solutes, such as sodium chloride, is higher in the surrounding medium (hypertonic), then water tends to leave the cell. The cell membrane shrinks away from the cell wall (an action called plasmolysis), and cell growth is inhibited. Normal cell Plasmolyzed cell

49. Control of microbial growth Definitions: Sterilization – the process of destroying all forms of microbial life on an object or in a material. Disinfection – the process of destroying vegetative pathogens but not necessary endospores. Antisepsis – chemical disinfection of skin, mucous membranes or other living tissues