microbes & environment

• Why are food preservation methods effective?

  They limit microbial growth and contamination
• What have microbes colonized on Earth?

  Every surface and can survive in space
• What defines an extremophile?

  A microorganism living in extreme conditions

  
• What is the pH range for hyperacidophiles?

  Less than pH 3
• What is the optimal pH range for neutrophiles?

  pH 5.5 to 8
• How do many enteric pathogens cope with low pH?

  They can tolerate low pH environments
• What is the problem faced by organisms in low pH environments?

  Maintaining pH homeostasis inside the cell

  
• What is one mechanism organisms use to cope with low pH?

  Active proton (H+) pumping

  
• What is a solution for coping with high pH?

  Activation of antiporter systems
• How do many foods control microbial growth?

  By having low or high pH levels
• What is the classification of organisms based on temperature?

  Psychrophile, Mesophile, Thermophile, Hyperthermophile

  
• What is a problem faced by organisms at high temperatures?

  Proteins denature and small molecules become unstable
• How do heat-stable proteins differ from those in mesophiles?

  They have more ionic bonding and shorter lengths
• What helps DNA remain functional at high temperatures?

  Unique enzymes like reverse DNA gyrase
• How do membranes cope with high temperatures?

  By containing more saturated fatty acids
• What is a basic biological difference between Bacteria and Archaea cell membranes?

  Archaea lack fatty acids and have tetraethers

  
• What is a solution for coping with low temperatures?

  Increase membrane fluidity with unsaturated fatty acids
• How do microbes respond to heat?

  Heat denatures enzymes and proteins
• What is the effect of cold temperatures on microbes?

  It usually stops or slows their growth
• What is the challenge of low water availability for organisms?

  Maintenance of turgor pressure inside the cell
• What is the difference between microbiota and microbiome?

  Microbiota refers to the community; microbiome is their genetic material
• How is water activity (aw) defined?

  Vapor pressure of solution divided by pure water
• What is the water activity of pure water?

  aw = 1
• What are the hotspots for microbial life in the human body?

  • Nasal tract
  • Oral tract
  • Skin
  • Gastrointestinal tract
  • Urogenital tract
• What are the two types of microbiota in the human body?

  Native/resident and transient microbiota
• What do halophiles need to maintain?

  Water in their cytoplasm
• How many microbial and human cells are estimated to be in the body?

  Approximately $10^{13}$ of each
• What is a solution for xerophiles coping with desiccation?

  Production of osmoprotectants like trehalose
• How do halophiles maintain ion balance?

  By accumulating K+ and Cl- ions

  
• What percentage of the human genome is genetically identical among humans?

  99.9%
• What is a problem faced by organisms under high pressure?

  Membrane fluidity and protein misfolding
• What are obligate aerobes?

  Organisms that require oxygen to live
• What is the role of superoxide dismutase (SOD)?

  To neutralize superoxide free radicals
• What does catalase do in organisms?

  Converts hydrogen peroxide to water and oxygen
• How similar is the microbiota on your skin or gut to that of your neighbor?

  Only 10-20% similar in species
• How many species are in the collective human gut microbiota?

  Over 35,000 species
• What is the typical bacterial count in the gut?

  Approximately $10^{13}$ bacteria
• How many carbohydrate-digesting enzymes does the human genome have?

  20 carbohydrate-digesting enzymes
• How many enzymes does Bacteroides thetaiotaomicron have?

  More than 260 enzymes
• What were the goals of the Human Microbiome Projects?

  • Analyze microbiota of different body sites
  • Study impact of gut microbiome on health