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Microbiology           An Evolving Science                                Second EditionJoan Slonczewski and John Foster  ...
Chapter Overview● How the environment limits growth● The microbial response to temperature● How microbes cope with pressur...
IntroductionMicrobes have both the fastest and the slowest growth rates of known organisms - Some hot-springs bacteria can...
Environmental Limits of          Microbial Growth“Normal” growth conditions  - Sea-level; temperature 20-40 o C; neutral  ...
The environmental habitat (such as high salt or low pH) that a species inhabits is based on one main criterion - The toler...
Global approaches used to study gene expression allow us to view how organisms respond to changes in their environment - D...
Figure 5.1             7
Table 5.1            8
Changes in TemperatureA bacterial cell’s temperature matches that of  its immediate environmentChanges in temperature impa...
Changes in TemperatureMicroorganisms can be classified by their growth temperature - Psychrophiles ~ 0-20o C - Mesophiles ...
Figure 5.2             11
Figure 5.3 Figure 5.4              12
Heat-Shock ResponseRapid temperature changes experienced during growth activates batches of stress response genes - Result...
Variations in PressureBarophiles or piezophiles are organisms adapted to grow at very high pressures - Up to 1,000 atm (10...
Figure 5.5             Figure 5.6                          15
Changes in Water ActivityWater activity (aw) is a measure of how much water is available for useOsmolarity is a measure of...
Minimizing Osmotic StressIn addition to moving water, microbes have at  least two mechanisms to minimize osmotic  stress  ...
Changes in Salt ConcentrationsHalophiles require high salt concentrations - From 2-4 M NaCl (10-20% NaCl) - For comparison...
Changes in pHFigure 5.11                              19
Changes in pHAll enzyme activities exhibit optima, minima,  and maxima with regard to pHBacteria regulate internal pH  - W...
Changes in pHThree classes of organisms are differentiated by the pH of their growth range - Neutralophiles grow at pH 5-8...
The cyanobacterium Spirulina has high concentrations of carotene, giving it a distinct pink color - It is also a major foo...
pH HomeostasisWhen cells are placed in pH conditions below the optimum, protons can enter the cell and lower internal pH t...
Figure 5.17              24
Oxygen As An Electron AcceptorMany microorganisms use oxygen as a terminal electron acceptor in a process called aerobic r...
Microbial Responses to OxygenStrict aerobes can only grow in oxygenMicroaerophiles grow only at lower O2 levelsStrict anae...
Oxygen-related growth zones in a standing test tube  Figure 5.19                                            27
Generation and destruction of reactive oxygen species (ROS)                            Figure 5.20                        ...
Culturing Anaerobes in the LabThree oxygen-removing techniques are used today 1. Special reducing agents (thioglycolate) o...
Figure5.21         30
Microbial Response to StarvationStarvation is a stress that can elicit a  “starvation response” in many microbes  - Enzyme...
Microbial Response to StarvationSome organisms growing on nutrient-limited agar can even form colonies with intricate geom...
Oligotrophic BacteriaIn natural ecosystems, most microbes appear  to be oligotrophs, organisms with a high  rate of growth...
Humans Influence Microbial EcosystemsMaximum diversity in an ecosystem is maintained, in part, by the different nutrient- ...
Humans Influence Microbial EcosystemsEutrophication is the sudden infusion of large quantities of a formerly limiting nutr...
Control of MicrobesA variety of terms are used to describe  antimicrobial control measures  - Sterilization: Killing of al...
Microbes die at a logarithmic rateDecimal reduction time (D value) is the length of time it takes an agent or condition to...
Physical AgentsHigh temperature - Moist heat is more effective than dry heat - Boiling water (100o C) kills most cells - K...
Figure5.26         39
Physical AgentsPasteurization - Many different time and temperature combinations can be used - LTLT (low-temperature/long-...
Physical AgentsCold - Low temperatures slow down growth and preserve strains - Refrigeration temperatures (4-8 o C) are us...
Physical AgentsFiltration  - Micropore filters with pore sizes of 0.2 µm  can remove microbial cells, but not viruses,  fr...
Air can also be sterilized by filtrationLaminar flow biological safety cabinets  force air through HEPA filters           ...
Physical AgentsIrradiation - Ultraviolet light    - Has poor penetrating power    - Used only for surface sterilization - ...
Chemical AgentsA number of factors influence the efficacy of a  given chemical agent, including: - The presence of organic...
The Phenol CoefficientThe phenol coefficient test compares the effectiveness of disinfectants    Table 5.3                ...
Commercial Disinfectants and        AntisepticsThese include: - Ethanol - Iodine (Wescodyne and Betadine) - Chlorine - All...
Figure5.30         48
AntibioticsAntibiotics are chemical compounds synthesized  by one microbe that kill or inhibit the growth of  other microb...
Effect of ampicillin (a penicillin derivative) on  E. coli  Figure  5.32                                                50
Biological Control of MicrobesBiocontrol is the use of one microbe to control  the growth of another  - Probiotics contain...
Chapter Summary● Global analysis of genes and proteins allow us to  study how microbes react to environmental changes● Mic...
Chapter Summary● Cells treated with antimicrobials die at a logarithmic  rate● Physical agents used to control microbes in...
Concept QuizMicrobes that grow at temperaturesbetween 40°C and 80°C are called:a) psychrophiles.b) mesophiles.c) thermophi...
Concept QuizBacteria cannot grow in solutions with veryhigh concentrations of sugar becausea) bacteria cannot digest pure ...
Concept QuizPhysical agents used to prevent bacterialgrowth include:a) pasteurization, freezing, phages.b) irradiation, pr...
Concept QuizThe ______ coefficient test is used tocompare disinfectants.a) ethanolb) iodinec) phenold) chlorox            ...
Concept QuizMicrobes that grow at very high pressuresare called:a) osmophiles.b) mesophiles.c) barophiles.d) halophiles.  ...
Concept QuizThe D-value refers to the length of time ittakes an agent to kill ___% of the microbialpopulation.a) 50b) 90c)...
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  • Transcript of "Microbiology"

    1. 1. Microbiology An Evolving Science Second EditionJoan Slonczewski and John Foster Environmental5 Influences and Control of Microbial Growth PowerPoint® Lecture Outlines Prepared by Johnny El-Rady, University of South Florida Copyright © 2010 W. W. Norton & Company, Inc. Permission required for reproduction or display
    2. 2. Chapter Overview● How the environment limits growth● The microbial response to temperature● How microbes cope with pressure● The microbial response to changes in: water activity, salt concentrations, pH, and oxygen● Hungry microbes● The control of microbes: - Physical, chemical, and biological 2
    3. 3. IntroductionMicrobes have both the fastest and the slowest growth rates of known organisms - Some hot-springs bacteria can double in as little as 10 minutes, whereas deep-seas sediment microbes may take as long as 100 yearsThese differences are determined by nutrition and niche-specific physical parameters like temperature and pH 3
    4. 4. Environmental Limits of Microbial Growth“Normal” growth conditions - Sea-level; temperature 20-40 o C; neutral pH; 0.9% salt, and ample nutrientsAny ecological niche outside this window is called “extreme”, and organisms inhabiting them extremophiles Figure 1.1 4
    5. 5. The environmental habitat (such as high salt or low pH) that a species inhabits is based on one main criterion - The tolerance of that organism’s proteins and other macromolecular structures to the physical conditions within that nicheNote that multiple extremes in the environment can be met simultaneously Figure 1.1 5
    6. 6. Global approaches used to study gene expression allow us to view how organisms respond to changes in their environment - DNA microarrays assess which RNAs are made in a given organism at a given time or under a given condition - Two-dimensional protein gels achieve separation of proteins based on differences in each protein’s isoelectric point (first dimension) and molecular weight (second dimension) 6
    7. 7. Figure 5.1 7
    8. 8. Table 5.1 8
    9. 9. Changes in TemperatureA bacterial cell’s temperature matches that of its immediate environmentChanges in temperature impact every aspect of microbial physiologyEach organism has an “optimum” temperature, as well as minimum and maximum temperatures that define its growth limitsMicrobes that grow at higher temperatures can typically achieve higher rates of growth 9
    10. 10. Changes in TemperatureMicroorganisms can be classified by their growth temperature - Psychrophiles ~ 0-20o C - Mesophiles ~ 15-45o C - Thermophiles ~ 40-80o C - Hyperthermophiles ~ 65-121o CAll of these organisms have membranes and proteins best suited for their temperatures 10
    11. 11. Figure 5.2 11
    12. 12. Figure 5.3 Figure 5.4 12
    13. 13. Heat-Shock ResponseRapid temperature changes experienced during growth activates batches of stress response genes - Resulting in the heat-shock responseThe protein products include chaperones that maintain protein shape and enzymes that change membrane lipid compositionThis type of response has been documented in all living organisms examined so far 13
    14. 14. Variations in PressureBarophiles or piezophiles are organisms adapted to grow at very high pressures - Up to 1,000 atm (101 MPa, or 14,000 psi)Barotolerant organisms grow well over the range of 1-50 MPa, but their growth falls off thereafterNote that many barophiles are also psychrophiles because the average temperature at the ocean floor is 2 o C 14
    15. 15. Figure 5.5 Figure 5.6 15
    16. 16. Changes in Water ActivityWater activity (aw) is a measure of how much water is available for useOsmolarity is a measure of the number of solute molecules in a solution, and is inversely related to awAquaporins are membrane-channel proteins that allow water to traverse the membrane much faster than by diffusion - Help protect the cell from osmotic stress 16
    17. 17. Minimizing Osmotic StressIn addition to moving water, microbes have at least two mechanisms to minimize osmotic stress - In hypertonic media, bacteria protect their internal water by synthesizing or importing compatible solutes (E.g.: Proline or K+) - In hypotonic media, pressure-sensitive or mechanosensitive channels can be used to leak solutes out of the cell 17
    18. 18. Changes in Salt ConcentrationsHalophiles require high salt concentrations - From 2-4 M NaCl (10-20% NaCl) - For comparison, seawater is ~ 3.5% NaCl Figure 5.8 18
    19. 19. Changes in pHFigure 5.11 19
    20. 20. Changes in pHAll enzyme activities exhibit optima, minima, and maxima with regard to pHBacteria regulate internal pH - When environment is in a similar pH rangeWeak acids can pass through membranes - Disrupt cell pH homeostasis, and thus will kill cells - This phenomenon is used to preserve foods 20
    21. 21. Changes in pHThree classes of organisms are differentiated by the pH of their growth range - Neutralophiles grow at pH 5-8 - Include most pathogens - Acidophiles grow at pH 0-5 - Are often chemoautotrophs - Alkaliphiles grow at pH 9-11 - Typically found in soda lakes 21
    22. 22. The cyanobacterium Spirulina has high concentrations of carotene, giving it a distinct pink color - It is also a major food for the Figure 5.15 famous pink flamingo 22
    23. 23. pH HomeostasisWhen cells are placed in pH conditions below the optimum, protons can enter the cell and lower internal pH to lethal levelsMicrobes can prevent the unwanted influx of protons by exchanging extracellular K+ for intracellular H+ when the internal pH becomes too lowUnder extremely alkaline conditions, the cells can use the Na+/H+ antiporter to bring protons into the cell in exchange for expelling Na + 23
    24. 24. Figure 5.17 24
    25. 25. Oxygen As An Electron AcceptorMany microorganisms use oxygen as a terminal electron acceptor in a process called aerobic respirationFigure 5.18 25
    26. 26. Microbial Responses to OxygenStrict aerobes can only grow in oxygenMicroaerophiles grow only at lower O2 levelsStrict anaerobes die in least bit of oxygenFacultative anaerobes can live with or without oxygenAerotolerant anaerobes grow in oxygen while retaining a fermentation-based metabolism 26
    27. 27. Oxygen-related growth zones in a standing test tube Figure 5.19 27
    28. 28. Generation and destruction of reactive oxygen species (ROS) Figure 5.20 28
    29. 29. Culturing Anaerobes in the LabThree oxygen-removing techniques are used today 1. Special reducing agents (thioglycolate) or enzyme systems (Oxyrase) can be added to ordinary liquid media 2. An anaerobe jar 3. An anaerobic chamber with glove ports - O2 is removed by vacuum and replaced with N2 and CO2 29
    30. 30. Figure5.21 30
    31. 31. Microbial Response to StarvationStarvation is a stress that can elicit a “starvation response” in many microbes - Enzymes are produced to increase the efficiency of nutrient gathering and to protect cell macromolecules from damageThis response is usually triggered by the accumulation of small signal molecules such as cAMP or guanosine tetraphosphate 31
    32. 32. Microbial Response to StarvationSome organisms growing on nutrient-limited agar can even form colonies with intricate geometrical shapes that help the population cope, in some unknown way, to food stressFigure5.22 32
    33. 33. Oligotrophic BacteriaIn natural ecosystems, most microbes appear to be oligotrophs, organisms with a high rate of growth at low solute concentrations - Indeed, they require low nutrient levels to surviveSome oligotrophic bacteria have thin extensions of their membrane and cell wall called prothecaes (stalks) - These expand the surface area of the cell and increase nutrient-transport capacity 33
    34. 34. Humans Influence Microbial EcosystemsMaximum diversity in an ecosystem is maintained, in part, by the different nutrient- gathering profiles of competing microbes Figure 5.23 34
    35. 35. Humans Influence Microbial EcosystemsEutrophication is the sudden infusion of large quantities of a formerly limiting nutrient - It can lead to a “bloom” of microbes, which can threaten the existence of competing species Figure 5.24 35
    36. 36. Control of MicrobesA variety of terms are used to describe antimicrobial control measures - Sterilization: Killing of all living organisms - Disinfection: Killing or removal of pathogens from inanimate objects - Antisepsis: Killing or removal of pathogens from the surface of living tissues - Sanitation: Reducing the microbial population to safe levels 36
    37. 37. Microbes die at a logarithmic rateDecimal reduction time (D value) is the length of time it takes an agent or condition to kill 90% of the populationFigure5.25 37
    38. 38. Physical AgentsHigh temperature - Moist heat is more effective than dry heat - Boiling water (100o C) kills most cells - Killing spores and thermophiles usually requires a combination of high pressure and temperature - Steam autoclave - 121o C at 15 psi for 20 minutes 38
    39. 39. Figure5.26 39
    40. 40. Physical AgentsPasteurization - Many different time and temperature combinations can be used - LTLT (low-temperature/long-time) - 63o C for 30 minutes - HTST (high-temperature/short-time) - 72o C for 15 seconds - Both processes kill Coxiella burnetii, the causative agent of Q fever 40
    41. 41. Physical AgentsCold - Low temperatures slow down growth and preserve strains - Refrigeration temperatures (4-8 o C) are used for food preservation - For long-term storage of cultures - Placing solutions in glycerol at -70 o C - Lyophilization or freeze-drying 41
    42. 42. Physical AgentsFiltration - Micropore filters with pore sizes of 0.2 µm can remove microbial cells, but not viruses, from solutions Figure 5.27 42
    43. 43. Air can also be sterilized by filtrationLaminar flow biological safety cabinets force air through HEPA filters Figure 5.28 43
    44. 44. Physical AgentsIrradiation - Ultraviolet light - Has poor penetrating power - Used only for surface sterilization - Gamma rays, electron beams and X-rays - Have high penetrating power - Used to irradiate foods and other heat- sensitive items 44
    45. 45. Chemical AgentsA number of factors influence the efficacy of a given chemical agent, including: - The presence of organic matter - The kinds of organisms present - Corrosiveness - Stability, odor, and surface tension 45
    46. 46. The Phenol CoefficientThe phenol coefficient test compares the effectiveness of disinfectants Table 5.3 46
    47. 47. Commercial Disinfectants and AntisepticsThese include: - Ethanol - Iodine (Wescodyne and Betadine) - Chlorine - All of the above damage proteins, lipids, and DNA - Are used to reduce or eliminate microbial content from objects 47
    48. 48. Figure5.30 48
    49. 49. AntibioticsAntibiotics are chemical compounds synthesized by one microbe that kill or inhibit the growth of other microbial speciesPenicillin mimics part of the bacterial cell wall - Prevents cell wall formation and is bactericidal Figure 5.31 49
    50. 50. Effect of ampicillin (a penicillin derivative) on E. coli Figure 5.32 50
    51. 51. Biological Control of MicrobesBiocontrol is the use of one microbe to control the growth of another - Probiotics contain certain microbes that, when ingested, aim to restore balance to intestinal flora - Lactobacillus and Bifidobacterium - Phage therapy aims to treat infectious diseases with a virus targeted to the pathogen - A possible alternative to antibiotics in the face of rising antibiotic resistance 51
    52. 52. Chapter Summary● Global analysis of genes and proteins allow us to study how microbes react to environmental changes● Microbes are classified by growth temperature: - Psychrophiles, mesophiles, and thermophiles● Barophiles can grow at very high pressures● Halophiles require high salt concentrations● Microbes are classified by pH range: - Acidophiles, neutralophiles, and alkaliphiles● Microbes are classified by their O2 requirements: - Aerobes, facultative, microaerophiles, and anaerobes 52
    53. 53. Chapter Summary● Cells treated with antimicrobials die at a logarithmic rate● Physical agents used to control microbes include: - Autoclaving, Pasteurization, refrigeration, filtration, and irradiation● Chemical agents used to control microbes include: - Antiseptics and disinfectants● Antibiotics selectively control microbial growth● Biological control of microbes include the use of probiotics and phage therapy 53
    54. 54. Concept QuizMicrobes that grow at temperaturesbetween 40°C and 80°C are called:a) psychrophiles.b) mesophiles.c) thermophiles.d) extreme thermophiles. 54
    55. 55. Concept QuizBacteria cannot grow in solutions with veryhigh concentrations of sugar becausea) bacteria cannot digest pure sugar.b) sugar raises the solution’s osmolarity.c) sugar lowers the solution’s osmolarityd) sugar raises the solution’s pH.e) sugar lowers the solution’s pH. 55
    56. 56. Concept QuizPhysical agents used to prevent bacterialgrowth include:a) pasteurization, freezing, phages.b) irradiation, probiotics, filtration.c) autoclaving, irradiation, freezing.d) antibiotics, refrigeration, pasteurization. 56
    57. 57. Concept QuizThe ______ coefficient test is used tocompare disinfectants.a) ethanolb) iodinec) phenold) chlorox 57
    58. 58. Concept QuizMicrobes that grow at very high pressuresare called:a) osmophiles.b) mesophiles.c) barophiles.d) halophiles. 58
    59. 59. Concept QuizThe D-value refers to the length of time ittakes an agent to kill ___% of the microbialpopulation.a) 50b) 90c) 99d) 100 59
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