Anhydrobiosis:
The ability to dry out completely and rehydrate again. Employed by small aquatic animals, protozoa, bacteria and plants. Lose all water and regain metabolic activity.
examples of anhydrobiosis
EXAMPLES:
1) Tardigrades
2) Nematodes
3) Rotifers
4) Springtails
5) Midge larvae
6) Resurrection plants
- All are small, have little/no control over water loss from body, generally aquatic inhabitants where there are, we/dry seasons
Tardigrades + adaptions
- Water bears which live on thin film of water on hydrated mosses, soil and temporary pools
- Phylogenetic group between arthropods and nematodes
Adaptions: - They are polyextremophiles (tolerate desiccation, exposure to toxic chemicals, low temperatures, vacuum, high pressure, radiation, extreme pH and anoxia
- Mediated by synthesis of bioprotectants (carbohydrates and proteins), free radicals, specific phospholipids and DNA repair mechanisms
Rotifers
- Fresh water animals with reduced bodies
- Polyextremophiles
- Fully asexual (only organisms which has no sexual reproduction in millions of years
Midge Larvae
- Polypedilum vanderplankii (insect)
- Live in ephemeral pools in Africa
- Largest known anhybiont, takes 45 minutes to resurrect to previous activity
- Cells highly drought resistant BUT not all cells can re-establish metabolic activity
- Larvae have unusual lipid and sugar composition
ressurection plants
- Selaginella lepidophylla (False rose of Jericho), native to chuhuahuan desert
- Reduced roots, thick leaves, survives decades without water
- Able to resurrect within few hours of watering
- Unusual lipid sugar composition
Genetic adaptions
- Expression of specific proteins induced by desiccation
- Small heat shock proteins (SHSPs)
- Late embryogenesis abundant proteins (LEA)
o Evidence: magnolia seeds from 2,000 years old flowered in 1994
o LEA proteins abundant, a-helix rich, heat stable and hydrophilic proteins
o Can function of chaperones or stabilise cytoskeleton
o Dehydrins: group of LEA proteins, bigger and more complex, hydrophilic and range of biological functions
2) Biochemical adaptations
- Accumulation of non-reducing disaccharides (sugars not metabolised by cell)
- Trehalose: Tardigrades, nematodes and yeast (detected by HPLC analysis) Trehalose replaces other sugars during dehydration as has a great water retention capacity. Rapid conversion to glycogen upon rehydration in anhydrobiotes.
Importance of water for membrane function
1) Osmosis
2) Vesicle transport
3) Membrane fusion
4) Pathogenesis
5) Irreversible damage of membrane components
- Hard to protect due to lipid membrane
Vitrification
: Transformation of the cytoplasm into a glassy state because of freezing/ drying. This retains physical properties of liquid state and is key to long-term survival
Glass is physically solid/brittle but thermodynamically liquid. IT changes the physics of water between call and maintains organised state
Protects the membrane and proteins. Without water the lipids are lost
Creates layer between lipids = traps water
vitrification process
- Cytoplasm transformed through trehalose
- Cohesive forces between cytosolic components increases (stabilised cells macromolecules, in membranes water replaced by sugars to prevent close approach of lipids)
- High molecular packing and viscosity = low molecular mobility
practical applications
- LEA proteins = cellular stability in industry and medicine, can engineer resistant microbes with LEA proteins
- Trehalose = drought resistance in plants, spray plants with precursors of trehalose or new crops which produce trehalose
- Improved biological stability, biological and medical applications, space program development
- HydRIS vaccines: Deliver vaccines without refrigeration using a coat of trehalose. Can also be used in eye drops, stable at room temperature over several years
Biological discoveries arising from study of anhydrobiotes
1) Asexual rotifers escape lethal fungal parasites by drying up and blowing away/ dispersing
2) Loss of body segments for tardigrades
o HOX genes: Contain unusual number for development while lacking some other proteins
o Loss intermediate body section as unneeded
o Organisms need time to accumulate proteins for survival in dehydration
o Cytosolic/secreted/ mitochondrial heat soluble protein expression in tardigrades
o CAHS: Proteins used to confer tolerance to desiccation as alter vitrification properties in vivo
3) Anhydrobiotes and survival in outer space
o Bio-risk space research of animals and plants exposed to space vacuum
o Organisms taken to space
o 2008 tardigrades survive exposure to space, space vacuum found to have minor effect on survival
o Some survival after receiving a dose of UV radiation of more than 7,000 kJm-2 under space vacuum
o Unknown survival mechanism
o Current experiments: Phobos-Grunt 2009-2011:
Mission to collect soil from Phobos (mars satellite) and to bring samples to Earth for research
Larvae of P. vanderplankii are included to test influence of long-term spaceflight on resting stages of invertebrates
