Environmental Limits on Microbial Growth

Transcription

1 Environmental Limits on Microbial Growth n Temperature n ph n Osmolarity n Oxygen n Pressure 2009 W. W. Norton & Company, Inc. 1

2 Changes in Temperature n Growth rate increases with temperature n Proteins denature if temperature too high Microbial proteins adapted to temperature range: n Psychrophiles Cold: O C 20 C n Mesophiles 12 C 45 C n Thermophiles 40 C 80 C n Extreme thermophiles 65 C 113 C 2009 W. W. Norton & Company, Inc. 2

3 Response to Temperature n Heat shock response Occurs at high end of temperature range Emergency proteins produced Help keep proteins from denaturing Induced by many stressful conditions n Heat n High salt concentrations n Arid conditions 2009 W. W. Norton & Company, Inc. 3

4 Variations in Pressure n Barophiles Adapted to high pressures n Up to 1,000 atm n Barotolerant organisms Grow at high, but not very high pressure n Barosensitive organisms Die at high pressure n Most typical bacteria, all mammals 2009 W. W. Norton & Company, Inc. 4

5 Changes in Water Activity n Solutes raise osmolarity n High osmolarity reduces available water n Osmotic pressure can burst membranes Low osmotic pressure outside cell n Mechanosensitive channels relieve stress n Release cell contents High osmotic pressure outside cell n Cells synthesize osmolytes n Increase internal osmolarity 2009 W. W. Norton & Company, Inc. 5

6 Changes in Water Activity n Halophiles n Require high concentration of NaCl 2 4 M (10x seawater) Live in salt seas 2009 W. W. Norton & Company, Inc. 6

7 Changes in ph n Enzymes only work in narrow ph range Amino acids must have correct charges n ph levels alter concentration of H + n Bacteria regulate internal ph When environment is in similar ph range n Weak acids can pass through membranes Disrupt cell ph homeostasis, kills cells Good food preservatives 2009 W. W. Norton & Company, Inc. 7

8 Changes in ph n Neutralophiles Grow at ph 5 8 Include bacteria in gut n Acidophiles Grow at ph 0 5 n Some grow in stomach acid n Some in sulfuric acid springs n Alkalophiles Grow at ph 9 11 n Found in soda lakes 2009 W. W. Norton & Company, Inc. 8

9 Oxygen as Electron Acceptor n Aerobes O 2 is ultimate electron acceptor Very strong electron acceptor Can oxidize, damage proteins n Anaerobes Reactive oxygen species (ROS) produced n Oxidize, damage proteins n Microaerophiles Can tolerate low levels of O 2 n Catalase inactivates ROS 2009 W. W. Norton & Company, Inc. 9

10 Other Electron Acceptors n Anaerobes pass electrons to different ultimate electron acceptors Anaerobic respiration n Inorganic electron acceptors Nitrate nitrite, thiosulfate Fermentation n Organic electron acceptors n Thrive in anaerobic environments Early Earth, deep water, lower gut 2009 W. W. Norton & Company, Inc. 10

11 Nutrient Deprivation, Starvation n Lack of nutrients slows cell metabolism Stimulates stress responses Cells spread farther Sporulation n Oligotrophs Most microbes Efficiently absorb N 2, PO 4 from nutrient-poor environments n Many nutrients at low environmental levels 2009 W. W. Norton & Company, Inc. 11

12 Controlling Microbial Growth n Microbes die at logarithmic rate n D-value = time to kill 90% of cells 2 D-values = time to kill 99% of cells n Antimicrobial agents decrease D-value Kills cells faster 2009 W. W. Norton & Company, Inc. 12

13 Physical Agents Temperature n Pasteurization 63 C for 30 minutes n Flash pasteurization 72 C for 15 seconds n Pasteurization treatments do NOT kill all cells Pasteurized food spoils eventually Leaves food tasting normal n UHT Ultra-high temperature 150 C for 3 seconds n Sterilizes all bacteria killed Used for creamers 2009 W. W. Norton & Company, Inc. 13

14 Physical Agents Temperature + Pressure n Autoclave = steam cooker 121 C, 15 psi (2 atm) for 20 minutes Kills all bacteria Kills endospores n Clostridium botulinum Botulism n Bacillus anthracis Anthrax 2009 W. W. Norton & Company, Inc. 14

15 Physical Agents Other Methods n Cold temperature refrigeration Slows growth, does not kill all bacteria n Freezing n Irradiation UV, X-rays, γ-rays n Filtration 2009 W. W. Norton & Company, Inc. 15

16 Chemical Agents n Disinfectants Kill all microbes Destroys eukaryotic cells as well n Cannot be used inside patients Bleach (chlorine), Betadyne (iodine) Soap Detergents 2009 W. W. Norton & Company, Inc. 16

17 Chemical Agents n Antibiotics Selectively kills microbes n May not work on all species Has minimal effect on eukaryotic cells n Can be used inside patients Interferes with bacterial-specific enzymes n Cell wall synthesis n Bacterial ribosome 2009 W. W. Norton & Company, Inc. 17

18 Penicillin n Many derivatives n Blocks cell wall synthesis n Growing bacteria lyse Slow-growing bacteria take longer to die Weakening cell wall 2009 W. W. Norton & Company, Inc. 18

19 Biological Agents n Probiotics Good bacteria n Displace disease organisms from tissues n Bacteriophages Phages Viruses that attack bacteria n Do not harm eukaryotes 2009 W. W. Norton & Company, Inc. 19