Topics:

Types of extreme environments present on Earth

Adaptations to cell structures required for survival in extreme environments

Residents of extreme cold environments

Residents of hydrothermal environments

Residents of acidic environments

Residents of high salt environments

Residents of alkaline environments

Survival under conditions of high-level radiation exposure

Importance of extremophiles

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 ~350o C with high H2S concentrations

Surrounding water is ~10-20oC 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

Continued

Topics:

Types of extreme environments present on Earth

Adaptations to cell structures required for survival in extreme environments

Residents of extreme cold environments

Residents of hydrothermal environments

Residents of acidic environments

Residents of high salt environments

Residents of alkaline environments

Survival under conditions of high-level radiation exposure

Importance of extremophiles

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 90oC, pH 1-5 –Oxidizes H2S (or So) 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