Osmoregulation in Bacteria: Compatible Solute Accumulation and Osmosensing

Hans Jörg Kunte

doi:10.1071/EN06016

RESEARCH FRONT

Previous Next Contents Vol 3(2)

Osmoregulation in Bacteria: Compatible Solute Accumulation and Osmosensing

Hans Jörg Kunte

+ Author Affiliations

- Author Affiliations

Federal Institute for Materials Research and Testing (BAM), 12205 Berlin, Germany. Email: hans-joerg.kunte@bam.de

Environmental Chemistry 3(2) 94-99 https://doi.org/10.1071/EN06016
Submitted: 15 February 2006 Accepted: 27 March 2006 Published: 5 May 2006

Environmental Context. Bacteria and Archaea have developed two basic mechanisms to cope with osmotic stress. The ‘salt-in-cytoplasm mechanism’ involves adjusting the salt concentration in the cytoplasm according to the environmental osmolarity and the ‘organic-osmolyte mechanism’ involves accumulating uncharged, highly water-soluble organic compounds in order to maintain an osmotic equilibrium with the surrounding medium. This highlight gives an overview of the osmoadaptation of prokaryotes employing the organic-osmolyte strategy and introduces a model explaining the fine-tuning of osmoregulatory osmolyte synthesis.

Abstract. Bacteria and Archaea have developed two basic mechanisms to cope with osmotic stress, the salt-in-cytoplasm mechanism, and the organic-osmolyte mechanism. Organic osmolytes or so-called compatible solutes can be accumulated in molar concentration in the cytoplasm and allow for the adaptation of bacterial cells to varying salt concentrations. The biosynthetic pathways of compatible solutes and different compatible solute transport systems are described. A model for osmoregulatory compatible solute accumulation is introduced.

Keywords. : Archaea — compatible solutes — halophilic — halotolerant — osmoregulated transporter

References

Glossary

Compatible solute. Non-ionic, highly water-soluble compound accumulated by the cell to achieve an osmotic equilibrium and which does not disturb the metabolism, even at high cytoplasmic concentrations.

Halophilic microorganism (halophile). Prokaryotic or eukaryotic organism that can grow well above 1.72 M NaCl (10%), although the growth optimum can be in the lower range of salinity.

Halotolerant microorganism. Organism that requires ~0.5 M NaCl for optimal growth (seawater), and can tolerate up to 1.72 M NaCl (10%).

Osmoadaptation. Ability to adapt to environmental fluctuations in osmolality.

Osmolality. A measure of the chemical potential of a solution at a particular temperature. Osmolality is expressed in moles per kilogram, where the denominator refers to the mass of the solvent, and the ‘mol’ refers to an osmole. Osmole does not represent a mass or number of osmotically active particles. Osmolality can be measured but not calculated.

Osmolarity. The sum of the molar concentrations of osmotically active solutes in solution expressed as moles of solute per litre solution (osM); osmolarity is an approximation for osmolality.

Osmolyte. Organic or inorganic solute accumulated by the cell to achieve and maintain an osmotic equilibrium.

Osmoprotectant. Inorganic or organic molecule/compound that stimulates growth of organism at high osmolality. Many, but not all, osmoprotectants are accumulated by the cell as osmolytes or compatible solutes.

Osmoregulation. Development of specific mechanisms to achieve osmoadaptation.

Osmosensor. Device that detects changes in osmolality of the surroundings of the cell. Known osmosensors so far are indirect sensors detecting changes in the composition of the cytoplasm (i.e. K⁺ concentration).

Turgor (pressure). Hydrostatic pressure built up in the cytoplasm owing to higher solute concentration inside the cell (therefore lower chemical potential of the cytoplasmic water) balancing the osmotic pressure difference between the cytoplasm and its surroundings. Turgor pressure renders the chemical potentials of cytoplasmic and extracellular water equal at equilibrium.

Osmoregulation in Bacteria: Compatible Solute Accumulation and Osmosensing

Glossary

Subscriber Login