MBIO 1010 - Lecture 17

• Psychrotolerant would fall between psychrophiles and mesophiles
• Above ~65ºC, only prokaryotic life forms exist

  • Chemoorganotrophic and chemolithotrophic species are present
  • No phototrophy above approx. 70oC
  • High prokaryotic diversity
  • Both Archaea and Bacteria are represented
• Thermophiles:

  • organisms with growth temperature optima between45ºC and 80ºC
  • Terrestrial hot springs, very active compost
• Hyperthermophiles:

  • organisms with optima greater than 80ºC
  • Inhabit hot environments, including boiling hot springs and sea floor hydrothermal vents that can experience temperatures in excess of 100ºC
  • Current temperature maximum record is held by an archaeon, Methanopyruskandleri, which can grow at 122oC
• Molecular adaptations to thermophily

  • Specific modifications provide thermal stability to enzymes and proteins
  • Modifications in cytoplasmic membranes to ensure heat stability
  • Bacteria have lipids rich in saturated fatty acids
  • Archaea have lipid monolayer rather than bilayer
• Hyperthermophiles produce enzymes widely used in industrial microbiology

  • Example: Taq polymerase used to automate the repetitive steps in the polymerase chain reaction (PCR) technique
  • Hydrolytic enzymes including proteases, cellulases and lipases
• Enzymes of thermophiles are more stable and tend to have higheractivity than their mesophilic counterparts
• What are the upper temperature limits for life?

  • New species of thermophiles and hyperthermophiles are still being discovered
  • Laboratory experiments with biomolecules suggest 140–150°C
• Hyperthermophiles may be the closest descendants of ancient microbes

  • Hyperthermophilic Archaea and Bacteria are found on the deepest, shortest branches of the phylogenetic tree
  • The oxidation of H2 is common to many hyperthermophiles
  • May have been the first energy-yielding metabolism
• • Thermophilic phototrophy - none passed 73 degrees
• • Thermophiilc chemoorganotrophy - nothing passed 110
• • Thermophilic chemolithotrophy - noting passed 122
• • Nothing passed 122 degrees discovered yet
• • Deepest shortest branches
  • Closest to the luca not distant away from it
  • Deep as in the entire tree (closest to the trunk)
  • Shortest as in the branch it self

   
• Pickling things have an adding acid which drop ph
• • Basic = alkaline
• • Internal ph stays neutral
• The pH of an environment greatly affects microbial growth
• Some organisms have evolved to grow best at low or high pH
• Most organisms grow best between pH 6 and 8→ neutrophiles
• Acidophiles

  • Organisms that grow best at low pH (<6)
• Alkaliphiles

  • Organisms that grow best at high pH (>9)
• The bottom line in the different adaptations is that:

  • The cytoplasmic membrane maintains its integrity at the growth pH
  • The internal pH of a cell must stay relatively close to neutral even though the external pH is highly acidic or basic
• Microbial culture media typically contain buffers to maintain constant pH

  • Each organism has an optimal pH for growth
  • Some bacteria produce acids
  • Acetic, lactic, sulfuric acid → decreases the pH
  • Some bacteria grow on amino acids
  • Releases ammonia→ increases the pH
• Water activity (aw): water availability; expressed in physical terms

  • Defined as the ratio of vapor pressure of air in equilibrium with a substance or solution to the vapor pressure of pure water
  • Reflects the amount of water that is interacting with ions and polar compounds in solution
• Typically, the cytoplasm has a higher solute concentration than the surrounding environment

  • Water will want to move into the cell creating turgor pressure
• When a cell is in an environment with a higher external solute concentration water will flow out

  • Cells can sometimes have mechanisms in place to prevent this
• Halophiles:

  • grow best at reduced water potential;
  • have a specific requirement for NaCl
  • Many marine microbes
• Extreme halophiles:

  • Require high levels of NaCl for growth
  • 15 – 30%
  • Ex) Microbes from Great Salt lake or the Dead Sea
• Halotolerant: can tolerate some reduction in water activity of environment but generally grow best at lower solute concentrations

  • Ex) Staphylococcus aureus
  • Lives on human skin
  • Grows best at low NaCl
  • But can tolerate up to 17.5%
• Osmophiles:

  • Organisms that grow with high sugar as solute
• Xerophiles: Organisms able to grow in very dry environments
• Specialized and rare organisms

  • Honey, jams and jellies do not have many organisms growing in them
  • Beef jerky and salted cod
• High osmolarity created with NaCl is used to select for acid producing microorganisms

  • Used for sauerkraut and pickle fermentation
  • Combination of high salt and low pH prevents the growth of most pathogens in the completed product
• Mechanisms for combating low water activity in surrounding environment involves increasing the internal solute concentration by:

  • Pumping inorganic ions from environment into cell
  • Synthesizing or concentrating organic solutes
  • Compatible solutes: compounds used by cell to counteract low water activity in surrounding environment
• Obligate aerobes:

  • require oxygen to live
  • grows only in the oxic zone at the top of the tube
• Strict anaerobes:

  • do not require oxygen and may even be killed by exposure
  • grpws only in the anoxic zone at the bottom of the tube
• Facultative aerobes:

  • can live with or without oxygen, they use oxygen when it is available
  • grows throughout the tube
  • better growth occurs in the oxic zone, where it can generate energy by aerobic respiration
• Aerotolerant anaerobes:

  • can tolerate oxygen and grow in its presence even though they cannot use it
  • grows well throughout the tube
  • doesn't use O2
  • not harmed by O2
• Microaerophiles:

  • can use oxygen only when it is present at levels reduced from that in air
  • grows in a narrow band between the oxic and anoxic zones
  • needs O2 for aerobic respiration
  • killed by atmospheric O2 levels