Lecture 1: Hypersaline Flashcards
why study extreme environments?
- origin of life on earth
- life on other planets
- extreme environments are common
- diverse communities
- polluted environments are extreme
- source of robust enzymes
What is an extreme environment?
- difficult to explain
- conditions extreme for one (prevent growth & may lead to death) organism are essential for another to grow
ultra-extreme environments
- they prevent the growth of, and may be lethal, to most organisms
- dominated by ‘extremeophiles’
- often v stable - obligate extremeophiles dominate
Hyper-saline environments: natural & artificial
Natural = Great salt lake, dead sea, kenyan soda lakes
Artificial = salterns (sea water left to evaporate to salt)
Semi-natural = Mono Lake, Owens valley, irrigated areas
hypersaline environments arise where ___ are high, ___ is low
evaporation rates high, rainfall low
- lots of rainfall on one side of mountain, prevailing winds, rives run down and other side = hypersaline
hyper-saline environments are found
deep sea vents, mud volcanoes, cold seeps, beneath ice sheets, within ice crystals
- wherever you have water flowing over geology (rocks) and there is a reason for conc effects (i.e. evaporation / high temp)
wherever ice forms you get
a hyper-saline environment
water freezes, solutes are excluded
characteristics of hyper-saline environments
- 10x saltier than sea water
- Great salt lake rich in Na+ and Cl-
BUT dead sea is Na+, Cl- with Mg2+ (other ions too) - pH pretty neutral
organisms in hyper-saline environments = obligate/facultative
Halotolerant = facultative up to 0.3M
Moderately halophilic = obligate in 0.2-2.0M
Extremely halophilic = obligate 3 - 5M
Woese et al 1990 produced what
universal phylogenetic tree
- w 3 domains (bacteria, archaea, eucarya)
- probably wrong, as diversity in archaea is so great, we have just not explored it
organisms found in hyper-saline environments?
- mixture (eukaryotes, bacteria & archaea)
studying hyper-saline environment challenges and how we solve these
- in more remote areas of world (transport, long way from lab etc, might be in national park)
- Salterns are useful (sea water evaporated for salt production)
- readily accessible & controllable
- artificial BUT good approximations of natural systems
- -found in many arid regions
Salterns: Commonly contain
Dunaliella salina (euk) & Halobacterium sp. (archaea)
Dunaliella salina in salterns
- Eukaryote
- tolerate wide range of salt conc
- photosynthetic over much of the range
- produces chlorophyll until salt concentrations rise too high
- then produces carotene as a photoprotectant & glycerol (commercially useful products)
Halobacterium in salterns
- archaea
- photosynthetic but in diff way to Dunaliella salina
problems with high salt concentrations for organisms
i.e halobacterium and Dunaliellla salina
OSMOTIC EFFECTS
- water lost from the cell
- dehydration
IONIC EFFECTS
- ions (particularly Na+) disrupt ionic bonds
- high salt can denature and precipitate proteins
how does Dunaliella salina cope with a fluctuating salt environments?
- under low salt conditions it is photosynthetic (stores starch)
- as salt conc rise, water leaves the cell & photosynthesis is inhibited
- set of salt tolerant enzymes is activated which convert STARCH to GLYCEROL
- – osmolyte (causes water to re-enter the cell)
- – compatible solute – protects proteins
- – photosynthesis restored
- if salinity declines (i.e. after rain) glycerol is converted back to starch
How does halobacterium cope with a fluctuating salt environments
- unusual lipids in the outer membrane makes them v robust
- proteins are highly salt tolerate (lots of acidic residues on their surface, interact w K+)
- obligate halophiles
- photosynthetic BUT utilise BACTERIORHODOPSIN
what is found at the bottom of salterns?
Microbial mats
- surface of the mat is dominated in cyanobacteria
- high O2 due to photosynthesis
what happens when all the water is gone? Bacteria & Archaea e.g.
cyanobacteria & Haloarucla
- – can survive in solid salt, yes, how long for? they cant grow, as no room to grow, but are they still doing something? suspended animation or metabolically active?
- – organisms can possibly survive for millions of years in solid salt utilising the carbon source deposited the same time as them
