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Bioenergetic aspects of halophilism
1Division of Microbial and Molecular Ecology, Institute of Life Sciences, and the Moshe Shilo Minerva Center for Marine Biogeochemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel. orena@shum.cc.huji.ac.il
Microbiology and Molecular Biology Reviews : MMBR
|June 5, 1999
Summary
High salt environments limit microbial metabolism due to high energy costs for salt adaptation. Energetics, not just free energy, determine which metabolic pathways, like those using KCl, can support life in extreme saline conditions.
Area of Science:
- Microbiology
- Biochemistry
- Environmental Science
Background:
- Microbial life thrives in diverse environments, including hypersaline habitats.
- High salt concentrations impose significant energetic challenges on microorganisms.
- Understanding metabolic limitations in extreme environments is crucial for microbial ecology.
Purpose of the Study:
- To investigate the impact of increasing salt concentrations on microbial dissimilatory metabolism.
- To correlate the occurrence of metabolic pathways with their associated free-energy changes.
- To elucidate the energetic costs of salt adaptation and their influence on microbial life.
Main Methods:
- Examined microbial diversity across a gradient of salt concentrations.
- Analyzed the free-energy changes of various dissimilatory reactions.
- Compared the energetic costs of different osmotic adjustment strategies (organic solutes vs. KCl).
Main Results:
- Certain metabolic pathways, including methanogenesis and sulfate reduction, are absent at the highest salinities.
- The occurrence of metabolic types correlates with the free-energy yield of dissimilatory reactions.
- High intracellular solute production and ion gradients represent significant energetic costs for halophiles.
Conclusions:
- The energetic cost of salt adaptation is a primary determinant of viable microbial metabolism in hypersaline environments.
- Using potassium chloride (KCl) as an intracellular solute is energetically more favorable than producing organic compatible solutes.
- This energetic advantage explains the prevalence of certain metabolic strategies, like those in Haloanaerobiales, and the absence of methanogens using H2 + CO2 in high-salt conditions.