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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
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
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