L6 : Life in Extreme Cold Flashcards
What are characteristics of Earth’s cryosphere?
Temp -90-5 deg
70% world’s fresh water
~33 km frozen H2O
~10-15% Earth’s surface
Glacier environments include polar and tropical
Describe features and organisms in supraglacial ecosystem?
Snow
Rivers, lakes, cryoconites, moraines
Photoauto, chemoauto, hetero, obligate paraistes
10^4-8
(majority of cryosphere life concentrated here)
Describe features and organisms in englacial ecosystem?
Ice
Crevices, caverns, ice flow, meltwater
Chemoauto, hetero, obligate parasites
10^1-3
Describe features and organisms in subglacial environment?
Under ice
Bedrock, basal meltwater, caverns, permafrost
Chemoauto, hetero, obligate parasites
10^2-8
Describe features and organisms in periglacial environment?
Ocean, air
Seafloor, seawater, supercooled cloud droplets, atmospheric deposition
Photoauto, chemoauto, hetero, obligate parasites
10^1-7
What are environmental stressors in the cryosphere?
Lack of liquid H2O
Lack of O2
Lack of nutrients/sunlight
High salt conc
Desiccation
Low/freezing temps
High UV and gamma radiation
Periodical freeze-thaw cycles
What are challenges for organisms in cryosphere?
Mechanical stress: cell/membrane puncture, cell component fragmentation
Freezing stress: Impaired enzymes, denatured proteins, lack O2/liquid H2O
Oxidative stress: heavy metal toxicity, metabolic byproducts (ROS), DNA/RNA damage
Osmotic stress: ice formation, salt, pH imbalance, pressure
Adaptations of organisms for crysophere?
Physical - compact bodies, exoskeletons, fat, blubber, fur
Behavioural - chemotaxis, competition/symbiosis, migration, burrowing
Biochemical - stress response systems, cell structure changes
What is the freezing effect on the cell?
Rigid, impermeable membrane and loss of element uptake/release
Struggle to regulate osmotic pressure, toxic byproducts/waste material
Ice formation can cause ruptures in membrane
Can lead to oxidative damage
What is the cell membrane stress response?
Modify lipid bilayer
- more unsaturated FAs/less saturated FAs
Change lipid composition
- more cholesterol-like molecules to ingrate into membrane
Increase in production of:
- Ice nucleating proteins
- Cryoprotectants (eg. trehalose)
- Desaturases (introduces double bond for unsaturated FA formation)
- Polar carotenoids (protection under stress)
- Membrane transporter channels
How does the cell membrane stress response help?
Lower phase transition temperature
Maintain membrane fluidity - less compact and rigid
Aid nutrient transport
What is ‘watermelon’ snow?
Algae produce pigments
Chalmydomonas produce carotenoids (astaxanthin) under stress
- sunscreen, antioxidant, absorb heat, reduce albedo
Chloromonas produce chlorophyll when in nutrient rich/favourable environments
- photosynthetic, sunscreen, reduces albedo
What is the cell environment stress response?
Proteins and components that assist with stress tolerance, osmotic regulation and protection against ice formation
What proteins and components are involved in cell environment stress response?
- Ice-nucleating proteins (INPs) promote ice formation outside cell to avoid intracellular damage
- Cryoprotectants lower cells freezing point
- Antioxidants (eg. glutathionine) repair ROS damage
- Osmolytes (eg. polyols, sugars) regulate intracellular osmotic pressure
- Biosulfactants (eg. glycolipids) reduce tension between liquids and solids
- Cold-sock proteins (CSPs) synthesised during cold-shock to stabilise cellular macromolecules
- Anti-freeze proteins (AFPs) bind to ice crystals and inhibition formation/growth
- Extracellular polymeric substrates (EPSs) bind and retain H2), protect cell from dehydration, form biofilms
What are problems against DNA in cold extremes?
High radiation
ROS production
Structural damage
What are DNA adaptations for cold extremes?
Low GC content = less energy for bond formation/less rigid DNA
Gene redundancy
DNA protection proteins (AFPs, CSPs, SSBs (ss binding proteins))
Pigments
Robust DNA repair
Under extreme dehydration, DNA observed in alpha formation (hollow core, comapct, more stable)
What are problems against RNA in cold extremes?
Leaky translation can result in protein isoforms
RNA folding (mRNA 2structure)
Affect tRNA binding to ribosome
Structural damage
What are RNA adaptations in cold extremes?
CSPs, SSBs stabilise ssRNA
High number of tRNAs
Modified tRNAs
Use of cryoprotectants and AFPs
Cold adapted polymerases
What are problems against proteins in cold extremes?
Freezing and structural damage
Protein misfolding
Protein denaturation/aggregation
Loss of enzyme activity
Damaged, unstable DNA/RNA
Oxidatie stress
What are protein adaptations in cold extremes?
Production of relevant proteins (above)
Chaperones to mediate folding
Use different proportions of AAs:
- Less Arg, Pro, Ala
- More Asp, Met, Gly
- Simpler bond formations, structural flexibility (esp catalytic sites)
Modify DNA regulation and enhance DNA repair mechanisms
Gene duplications to preserve function
What are energy source and metabolic adaptations in cold extremes?
Store glycogen, lipids, long chain FAs for prolonged energy release
Use alternative energy sources
Slow metabolic rate
Optimise light absorption.energy capture
Use anaerobic pathways to cope with O2 lack
Downregulate genes for ROS production and motility (use chemotactic responses)
Utilise symbiosis
Examples of organisms that utilise alternative metabolic pathways?
Methanogens
Sulfur-oxidising bacteria
Iron-oxidising bacteria
Hydrogen-oxidising bacteria
Organisms living in extreme cold
What is the reservoir of emerging pathogens?
Over 10,000 viral species in global glacial environments emerging as ice melts
Eg. Pandora-like virus, anthrax, H1N1, tomato mosaic virus
