Extreme Biology

Extreme Biology

Energy

• Living things use food as a source of energy

– Autotrophs make their own food.

Autotrophs capture the sun’s energy and use it along with water and carbon dioxide to make their own food.

• Auto (self)

• Troph ( feeder)

– Heterotrphs cannot make their own food. They get energy from the sun indirectly by eating autotrophs or other heterotrophs

• Hetero (other)

• Troph (feeder)

Universal Tree of Life: 3 Domain System

Bacteria and Archaea are both prokaryotes

Extreme Environments on Earth

1. Sea Ice (extreme cold)

2. Hydrothermal vents (extreme heat and high metal content) 3. Sulfuric Springs (extreme heat and highly acidic)

4. Salt Lake (extreme salt concentrations)

5. Soda Lake (extreme salt concentration and highly alkaline)

Cellular Targets of Adaptations to Extreme Environments

Cytoplasm: water, proteins, metabolites, salts

Nucleoid: Aggregated DNA Chromosome

Typically lipid bilayer

Typical Prokaryotic Cell

Life on Ice

 Over 75% of Earth’s biosphere is permanently cold (< 5°C)

 Much of the life present in the cold environs is planktonic growth of bacteria and archaea in frigid marine waters (~10⁴ cells/ml) (psychrophiles)

 Identified using rRNA techniques – 16S rRNA sequencing

– Fluorescent rRNA DNA probes

 At this point physiology of psychrophilic archaea/bacteria undetermined

 Cold adaptations: more fluid membranes, more structurally flexible proteins

Psychrophilic cyanobacteria

Methanogenium frigidum

Adaptations to Extreme Cold: Making More Fluid Membranes

More fluid membranes result from putting unsaturated/polyunsaturated fatty acids into the membrane

More Life on Ice: Algae

Algae living on the ice

(photosynthetic unicellular plant)

Lichen = symbiotic relationship between algae and fungi

Phytoplankton Krill

Polychaete Worms Living on Methane Ice

 It is thought that the worms eat the bacteria that are growing on the methane ice

Lake Vostoc: A model for Life on Europa?

Hydrothermal Vent Systems

Anatomy of A Vent

Hydrothermal Vents: Abiotic Conditions

 Extremely hot temperatures (> 350ºC [hydrostatic pressure of 265 atm prevents water from boiling until 460 ºC ])

 Extremely high pressures up to 1,000 atm

 Vents rich in minerals (eg. Iron oxides, sulfates, sulfides, manganese oxides, calcium, zinc, and copper sulfides)

 Hot waters anaerobic since solubility of oxygen decreases as water temperature increases

Hydrothermal Vents: Biotic Community

 Archaea and bacteria grow in or near vent chimneys, shown to live and reproduce at temp. of 115°C (hyperthermophiles)

 As of 5 years ago believed highest upper temp. for life was 105

°C, now expect hyperthermophiles may grow up to 160 °C [limit of ATP stability]

 Rich microbial communities grow at some distance from vent chimneys where temperatures are more moderate (8 - 12°C) due to mixing mixing with cold seawater (~2°C)

Hydrothermal Vent Ecosystems: The Prokaryotes

Methanococcus janaschii (85°C)

Pyrococcus furiosus (100°C)

Vent contact slide Aquifex aeolicus (95°C)

Thermotoga maritima (90°C)

Archaea Bacteria

Archaeoglobus fulgidus (83°C)

Thermal Adaptations Used By Hyperthermophiles for Survival

 Membrane: ether-linked membrane-lipids, monolayer membranes

 Protein: hydrophobic protein core, salt bridges, chaperonins

 DNA: Cation stabilization (Mg²⁺), Reverse DNA gyrase, DNA-Binding proteins (histones)

 General: compatible solutes?

Histone and DNA

Hydrothermal Vent Ecosystem: Tube Worms

 Vent water is ~350^o C with high H2S concentrations

 Surrounding water is ~10-20^oC

 Gutless tubeworms (Riftia have a mutualistic symbiosis with aerobic H2S- oxidizing bacteria (Thiomicrospira).

Vestimentiferan worms; Riftia pachyptile

Endosymbiosis in Tubeworms

Hydrothermal Vent Ecosystems: Bivalves

Calyptogena magnifica Bathymodiolus thermophilus

Hydrothermal Vent Ecosystems: “Snow Flurries” and Crabs

Flocs of sulfur bacteria Galatheid crabs

And Where There’s Crabs, Octopi Are Not Far Behind

Black Smokers – Sulfur Reducers

• Black smoker vents

• Found in deepest parts of the ocean

• Volcanic, mineral-enriched water outflows

• Rich in iron, sulfur compounds

• Very little/no oxygen

• Discovered in the 1970s

• Temps as high as 750 F (!!)

• Does not boil, though, due to extreme pressure at this depth

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Black Smoker Structure

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Black Smoker Ecology

• Deep sea exploration vehicles investigate black smokers in the 1980’s

• Much to everyone’s surprise, they find LIFE !!

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Black Smoker Ecology

• Not just life – fully-developed ecosystems!

• Crabs, shrimp, clams, Pompeii worms

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Pompeii Worms

• Tube worms anchored near black smoker vents

• Bottom end has very high temps; top end more like 70F

• Hot water flows through tubes; length as much as 10 feet!

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Pompeii Worms

• “Hairy” back is heat-resistant microbe mat (symbiotic with worm mucus)

• Red “feathers” include hemoglobin; separates hydrogen sulfide from vent flow

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Extreme Environments on Earth

1. Sea Ice (extreme cold)

2. Hydrothermal vents (extreme heat and high metal content) 3. Sulfuric Springs (extreme heat and highly acidic)

4. Salt Lake (extreme salt concentrations)

5. Soda Lake (extreme salt concentration and highly alkaline)

Life in Sulfur Springs (Hot and Acidic)

Abiotic conditions:

- high temperatures >30°C - low pH (< 4)

- high sulfur

 Sulfur-oxidizing, acid-loving, hyperthermophiles such as the archaeon Sulfolobus have been isolated from sulfur hot springs

Sulfolobus grows at 90^oC, pH 1-5

–Oxidizes H₂S (or S^o) to H₂SO₄ –Fixes CO₂ as sole C-source

 Acidophiles do not have low internal pH’s and have adapted to keep protons outside the cell

Other Acidic Environments and Denizens

Acid mine drainage  Acidophilic archaeon, Picrophilus oshimae, grows optimally at pH 0.7, cannot grow above pH 4

 Red alga Cyanidarium caldarium grows at pH of 0.5

 Archaeaon Ferroplasma acidarmanus thrives in acid mine drainage at pH 0 (has no cell wall)

 Acidophiles studied to date appear to have very efficient membrane-bound Na⁺/H⁺ pumps and membranes with low permeability to protons

High Salt Environments

Salt evaporation ponds

Great Salt Lake

 Low biodiversity; only home to halophilic organisms belonging to Archaea, Bacteria and some algae

 Extreme halophiles require at least 1.5 M NaCl for growth (most need 2 – 4 M NaCl for optimum growth)

 Cell lysis occurs below 1.5 M

 Membranes are stabilized by Na⁺

 Maintain high internal K⁺Cl^- to balance high external Na⁺Cl^-

 A number of halophiles have a unique type of

“photosynthesis”

 Multiple light-sensitive proteins

–Halorhodopsin (Cl^- transport, creating Cl- gradient which drives K⁺ uptake)

–Bacteriorhodopsin (photosynthesis?)

Halophilic Algae

Dunaliella salina

 Photosynthetic flagellate

 Red because of high

concentrations of beta-carotene

 On sensing high salinity, pumps out Na⁺ ions and replaces with K⁺ ions

 In high salt, will alter

photosynthetic pathway to produce glycerol (water-soluble, nonionic substance which prevents

dehydration) instead of starch

Halobacterium salinarum and Light-mediated ATP Synthesis

Halobacterium salinarum

 Halobacterium contain photopigments which are used to synthesize ATP as a result of proton motive force generation

cis-form

trans-form

light

Retinal chromophore of bacteriorhodopsin

High Salt Alkaline Environments: Soda Lakes

Lake Magadi (Soda lake in Kenya)

 Have very high pH (> 9) due to high levels of CO₃^2- ion

 Very few organisms can tolerate alkaline conditions (to date only alkalophilic prokaryotes have been isolated)

 Most alkalophilic organism,

cyanobacterium Plectonema, grows at pH of 13

 Alkalophile adaptations: pumps to pump out OH^-, efficient Na⁺/H⁺ to provide internal H⁺, modified

membranes

Cyanobacterium

Spirilina Natronobacterium

Survival Under Conditions of High Level Radiation Exposure: Deinococcus radiodurans

 Aerobic, mesophilic bacterium

 Extremely resistant to desiccation, UV and ionizing radiation -- Can survive 3-5 million rads (100 rads is lethal for humans)

 Contain variable numbers (4-10) of chromosomes

DNA Damage Repair in Deinococcus radiodurans

 Deinococcus radiodurans has very efficient DNA repair machinery

 DNA sheared by radiation will

reform within 24h

Importance of Extremophiles:Extremozymes

 Enzymes from extremophiles offer some important potential benefits:

 Hyperthermophiles

– Sugar conversions without microbial growth and contamination

 Psychrophiles

– Modification of flavor/texture of foods without microbial growth & spoilage

 Acidophiles

– Removal of sulfur from coal & oil

 Alkalophiles

– Cellulases that can be used in detergents

Importance of Extremophiles: Astrobiological Implications

Mars

Europa

 Extreme environments on Earth are thought to be very similar to extreme

environments that exist elsewhere in space

 Microorganisms that thrive in Earth extreme environments are thought to be likely candidates for the types of biota that may exist in extraterrestrial habitats

 Mars is postulated to have extremophilic regions including permafrost,

hydrothermal vents, and evaporite crystals

 Europa is thought to have a subsurface ocean

Extreme Life: Aquifex Aeolicus

• In the 1960’s, biologists

were interested in studying

“how extreme” life could be

• They knew that microbes lived in water downstream from hot springs in

Yellowstone National Park

• The springs themselves reached temperatures of

~85C (185 F) – near the boiling point of water

• The question: How far upstream (close to the hottest water) could microbes survive?

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Aquifex Aeolicus Surprise

• Biologists discovered bacteria in the hottest parts of the hot springs themselves

• These creatures survive – even thrive and

reproduce!! – at ~85C (185 F), near the boiling point of water

• Picture shows microbial mats (as in stromatolites) in Yellowstone hot spring

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Aquifex Aeolicus Properties

• These are very small bacteria

• Prokaryotes

• Genome structure is only 1/3 as long (complex) as E. coli (a model “simple” bacteria)

• Single DNA molecule in a circular chromosome

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Aquifex Aeolicus Metabolism

• A. aeolicus survives from H, O, CO₂, and mineral salts

• Requires oxygen for

respiration (so, not that primitive)

• But … no need for sunlight, nor sunlight-using food !!

• Purely chemical food source (in the presence of thermal energy from the water)

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The colors of Prismatic Spring in

Yellowstone come primarily from the hyperthermophile microbes in it