Life in Hypersaline Environments

1
Life in Hypersaline Environments

• Molly Burke
• EcoEvo 208

2
What is a hypersaline environment?

• Generally defined as those saltier than seawater
  (3.5 total dissolved salts)
• The two largest and best-studied hypersaline
  lakes are the Great Salt Lake (up to 27) and the
  Dead Sea (up to 35)

3
Problems to overcome

• Low levels of oxygen
• Denaturing effects of salts
• Osmotic pressure of the environment

4
Brine ShrimpArtemia franciscana

• How do they deal with salt?
• Life cycle
• Biochemistry

5
Artemia Life Cycle

• Females can produce dormant cysts in a
  suspended state of metabolism (dispause)
• Cysts are impermeable to NaCl
• Females produce cysts at salinities over 10, at
  which they are buoyant
• Cysts only hatch in aerobic conditions

6
Artemia Biochemistry

• Salt-tolerant organisms should contain stable
  macromolecules that can withstand the denaturing
  effects of salt
• Acidic residues prevent the denaturation that
  usually happens when proteins are exposed to high
  salt concentrations

7
Artemia Biochemistry

• (a) Malate dehydrogenase
• a halophilic enzyme
• (b) Lactate dehydrogenase
• a homologous enzyme that is nonhalophilic

Red spheres are acidic residues blue are basic
DasSarma and Arora 2001
8
Artemia Biochemistry

• Hand and Conte 1982
• Brine shrimp larvae cultured in artificial
  seawater containing 2.5 M NaCl maintain
  significantly higher levels of cytoplasmic malate
  dehydrogenase than larvae cultured in seawater
  containing 0.5 M NaCl

9
How else might brine shrimp tolerate
hypersalinity?

• Determine how they achieve isoosmotic balance
  with their environment
• Membrane kinetics
• Cytoplasmic solute concentration

10
References

• Hand SC, Conte FP. Larval brine shrimp malate
  dehydrogenase biosynthesis and temporal pattern
  related to environmental salinity. Journal of
  Experimental Zoology 1982. 219 17-27
• DasSarma S, Arora P. Halophiles. Encyclopedia
  of Life Sciences, Nature Publishing Group 2001.