Extreme Environments Extremes in terms of what human life can exist in. These can include temperature (high or low), pressure, acid or alkali and high salts.

DEEP SEA Open ocean the photic zone can extend to 300m, causing a good deal of biological growth down to 1,000m. Below this level (75% of ocean volume) the biological activity is less. 3 problems are faced Low temperature below 1,000m it is a constant C High pressure 1 atm/10m. eg at 1,000m it is? Low nutrient levels Phytoplankton falls to the sea bed as ‘marine snow’ which is seasonal following growth. The journey down takes over 1 month and 99% is already decomposed. Below 100m the bacteria are psychrophilic. Some bacteria isolated are barotolerant (down to ~ 300m), grow at atmospheric pressure, will not grow above 500atm.

4,000m to 6,000m are barophilic. Grow optimally at 400atm, still grow at 1 atm. From deeper waters get extreme (obligate) barophiles, optimally at atm. Not killed at 1atm, but very heat sensitive. Inc pressure decreases binding capacity of enzymes, so enzymes are folded in such a way as to minimise this. The membranes have an increase in the amount of unsaturated fatty acids in their membranes to keep the membrane fluid. They grow slowly as chemical reactions are slowed down. The have special high pressure porins expressed at high pressures. This and a few other genes are specifically expressed at high pressures

Temperature Classes Psychrophile – hyperthermophiles

Growth at cold temperatures. Psychrophile opt growth below 15 0 C and max below 20 0 C, grows at 0 0 C. Psychrotolerant grows at 0 0 C but opt C. Psychrophiles found in any permanently cold environment, can be rapidly killed by room temp. Best known are algae that grow in the bottom of sea ice in polar regions. Growing in summer months on the bottom of ice ~ 2m thick. In summer months also get alga growing under the surface of snowfields and glaciers giving it a red or green colour.

Summer snow algae

Psychrotolerant are found in water, milk, coconut water, soil and lots of other foods kept in a fridge. Growth is slow. These include bacteria, fungi, algae and protozoa. Psychrophilic enzymes have lower temp optimums and are denatured at moderate temperatures. More alpha helix and less beta sheet making them less rigid. More polar and less hydrophobic aa, to help keep protein flexible. More unsaturated fatty acid.

Sampling bacteria in Antarctica

High temperature environments are associated with hot springs and hydrothermal vents

Water can pick up a lot of minerals from the hot rocks and have various pH’s. Above 70 0 C there is very little Oxygen. The nutrients support a range of chemoorganotrophic and chemolithotrophic bacteria. As water flows away from the spring it cools down and you get a temperature gradient. This supports a range of bacteria including cyanobacteria below 74 0 C. As the temperature cools further, eukaryotic organisms can grow like the thermoacidophilic alga Cyanidium Caldarium temp max 56 0 C.

One very common aerobic organism are Thermus species which are aerobic chemoorganotrophs. They have a temp optimum ~70 0 C. This is near the limit of aerobic growth, why? The max temp that eubacteria have been isolated have been at 95 0 C. The only bacteria that have been found growing above this temp are archebacteria.

Hydrothermal Vents. Associated with moving tectonic plates on the ocean floor. Hot basalt and magma near the sea floor. Seawater seeping into it becomes superheated and rich in minerals. Two types of vents. Warm vents C and hot vents. Hot vents emit at C. The mineral rich liquid forms ‘black smokers’ as the mineral rich liquid mixes with cold water.

Vent Minerals

Tubeworms And Mussels

Vent video Tubeworm video

Energy source. The vent fluid has a high conc. of H 2 S, Mn 2+, H 2, CO, NH 4 +. These are used as inorganic energy sources by chemolithotrophs. CO 3 2- and HCO 3 - is fixed into organic carbon. There are large # sulphur oxidising bacteria, Thiobacillus, Thiothrix and Beggiatoa, fixing CO 2 at expense of H 2 S and S 2 O 3 2-.

Nutrition of animals. Chemolithotrophs live in symbiotic association with animals in the thermal vent. The 2m long tube worms have a modified gut with spongy tissue – trophosome (50% of it’s weight) loaded with S granules and large # S oxidising bacteria. These bacteria nourish the worm with excretion products and dead cells. The worm is red with blood (special Hb) that traps H 2 S, CO 2 and O 2 for the bacteria.

Tubeworms And Mussels

Hydrothermal fluid is emitted at C, could theoretically have bacteria there. At 2,600m water boils at C. Hyperthermophiles are known to live around the the plume coming from the chimney formed from the ppt minerals. The walls of the chimney are colonised by Methanopyrus oxidising H 2. Pyrolobus has been isolated from the plume growing at C, but may be able to grow at higher temps. Vent chimneys are colonised by the 6cm metazoan worm Alvinella or Pompeii worm.

Pompeii worm

pH

Organisms have optimum pH values for growth. Most microorganisms are neutrophiles pH opt Bacteria cannot survive if the internal pH drops below ~ 5.0. Acidophiles must maintain an internal pH above this or their proteins will denature. There membranes can be impermeable to protons. Thiobacillus are important acidophiles that oxidise sulphide minerals generating sulphuric acid, they are used to help leach Cu from low grade ore. They cause environmental problems of acid mine drainage from coal mining waste, acid and dissolved metals are toxic (inc Al). They need air to oxidise the pyrite, so coal below the surface is OK. Cyanidium caldarum and Sulfolabus acidocaldarius live in acidic hot springs.

Acid mine Drainage From coal mine

Osmotic – Halophiles. The water availability (activity) is also dept. on the conc. of solutes. The cytoplasm of cells usually has a higher solute conc. than the surrounding media so water tends to move in, balanced by cell wall.. Seawater 3.5%, marine organisms have a requirement for Na+. At high solute conc. water will tend to move out Mild halophile 1-6% Moderate 6-15% Extreme halophile 15-30% Organisms cope by using internal solutes, often organic compounds like glycine betaine, proline or glycerol to balance the osmotic pressure without damaging proteins or K+ (Halobacterium).