Life in the Extreme

Extreme Environments & Extremophiles

  • Extreme environments: Conditions that limit an organism's ability to perform essential functions like replication, protein biosynthesis, and energy acquisition.

  • Natural selection: Microorganisms evolve to be anatomically, behaviorally, and physiologically suited to thrive in extreme conditions.

  • Extremophiles: Organisms that thrive in extreme conditions. The term comes from Latin “extremus” (outermost) and “phila” (loving).

Examples of Extremophiles:

  • Microorganisms that haven't been cultured in the lab (e.g., Haloquadratum, Riftia pachyptila, Tardigrades, Planococcus halocryophilus).

  • Found across all domains of life.

Extreme Environments on Earth:

  • Microorganisms exist in various extreme environments, particularly where liquid water is available.

  • Studying life in extreme conditions on Earth helps explore the potential for life elsewhere in the universe.

Types of Extremophiles:

  1. Psychrophiles: Thrive in cold (below 0°C to 20°C, optimal <15°C).

  2. Mesophiles: Prefer moderate temperatures (20°C–45°C).

  3. Thermophiles: Grow best at hot temperatures (>45°C).

  4. Hyperthermophiles: Optimal growth at >80°C, dominated by archaea, no bacteria grow above 90°C.

Temperature-Specific Extremophiles:

  • Synechococcus (cyanobacteria): Grows between 52-73°C, produces carotenoid pigments for photosynthesis and UV protection.

  • Phormidium (cyanobacteria): Grows between 35-57°C, uses carotenoids for UV protection.

  • Calothrix (cyanobacteria): Grows between 30-45°C, a mix of thermophiles with different UV-protecting pigments (carotenoids, melanins).

Thermophiles – How They Cope with Heat

  • Cell membrane stability:

    • High proportion of saturated lipids in membranes.

    • Higher trans bonds (increased melting temperature).

  • Heat-stable proteins:

    • Increased ionic bonds for stability.

    • Protein stabilizing solutes (e.g., diglycerol phosphate, mannosylglycerate).

  • Nucleic acids:

    • Higher GC content, which increases thermal stability.

  • Record Thermophile:

    • Species: Geogemma barossi ("strain 121").

    • Record Temperature: 121°C (250°F).

    • Location: Isolated from black smoker hydrothermal vent at Juan de Fuca Ridge.

    • Domain: Archaea.

  • Evolution of Thermophiles:

    • Possible evolutionary scenarios include adaptation to high temperatures through genetic changes across the tree of life.

Notable Thermophiles:

  • Thermus aquaticus:

    • Discovered in Yellowstone hot spring (1965).

    • Grows best at 65-70°C.

    • Source of the heat-resistant enzyme Taq DNA polymerase, crucial for PCR, a method in molecular biology and DNA sequencing.

    • Nobel Prize: Kari Mullis (1993) for the invention of PCR.

Psychrophiles – How They Cope with Cold

  • Proteins:

    • Amino acid substitutions create instability to maintain flexibility in cold temperatures.

    • Fewer weak bonds (ionic and hydrogen bonds).

  • Cell membranes:

    • Higher proportion of unsaturated/short-chain fatty acids and more cis-bonds for flexibility.

  • Other Adaptations:

    • Antifreeze proteins and solutes (e.g., Glycine-Betaine): Prevent ice crystal formation.

    • Cold Shock Proteins: Chaperones that bind RNA to preserve its conformation.

  • Psychrophile Enzyme Example:

    • Enzymes in coldwater:

      • Amylase (breaks down starch).

      • Protease (digests proteins like grass and blood).

      • Proprietary enzyme that attacks guar, a thickener used in processed foods.

Alkaliphiles – How They Cope with High pH

  • Alkaliphiles: Organisms that thrive in environments with high pH (11-12).

  • Species Example: Nitrosomonas halophila.

    • Record: Grows optimally at pH 11-12.

    • Location: Isolated from Mongolian soda lakes.

    • Domain: Bacteria.

  • Adaptations:

    • Morphology: Grown at pH 10 with 0.6 M Na+ (high salt content).

    • Soda lake bacteria, like those from the Kulunda Steppe, are adapted to high pH and salinity.

Piezophiles – Organisms that Grow Under High Pressure

  • Definition: Piezophiles are organisms that grow optimally under high hydrostatic pressure (≥ 10 MPa).

  • Pressure Facts:

    • For every 10 meters of water depth, pressure increases by 1 atmosphere.

    • At ocean depths (~3,800 meters), the pressure is about 380 times greater than at the surface.

  • Adaptations to High Pressure:

    • Reduced cell division: Slower growth at extreme depths.

    • Modified membranes and transport proteins: Adjusted to function under high pressure.

    • Lipids with highly unsaturated fatty acids: Help maintain membrane fluidity under pressure.

  • Example:

    • Mariana Trench: Depth of 11 km, experiencing 1.1 kbar pressure, ~1,100 times greater than surface pressure.

Piezophiles – How They Cope with High Pressure

  • Piezophiles: Organisms that thrive under high hydrostatic pressure.

  • Species Example: Halomonas salaria.

    • Record: Grows at a pressure of 102 MPa (1002 atm).

    • Location: Isolated from saltwater in Anmyeondo, Korea.

    • Domain: Bacteria.

Radioresistant Organisms – Surviving Extreme Radiation

  • Radioresistant Species: Organisms that can withstand high levels of radiation.

  • Species Example: Deinococcus radiodurans (also known as "strange berry").

    • Record: Withstands 5,000 Gy of gamma radiation (for reference, 5 Gy can kill a human).

    • Location: Isolated from Oregon Agricultural Experiment Station.

    • Domain: Bacteria.

    • Discovery: Discovered in the 1950s, isolated from a tin of meat exposed to radiation thought to kill all life.

    • Adaptation: Has highly efficient DNA repair enzymes that excise mutations and reassemble fragmented chromosomes.

Metallotolerant Organisms – Surviving Extreme Metals

  • Metallotolerant Species: Organisms that thrive in high metal concentrations.

  • Species Example: Ferroplasma acidiphilum.

    • Record: Can survive in ~200 g/liter of metals.

    • Location: Isolated from acid mine tailings.

    • Domain: Archaea.

    • Adaptation:

      • Extracts energy from reduced iron, "eats" the metal, and leaves rust behind.

      • Uses metal as a structure-organizing element for cellular proteins.

Oligotrophs – Surviving in Nutrient-Scarce Environments

  • Oligotrophs: Organisms that can survive with very few nutrients.

  • Species Example: Pelagibacter ubique (SAR11).

    • Record: Can live with < 2 nM phosphate and < 100 nM nitrogen.

    • Location: Isolated from the Sargasso Sea.

    • Domain: Bacteria.