halophilism

The department is interested in the biology of salt loving organisms, mainly halophilic archaea. We attempt to unravel the characteristics of halophilic proteins which allow to withstand the extremely high intracellular salt concentrations detrimental to standard proteins. We experimentally. Additional subjects of interest are the metabolic capabilities of halophilic archaea, their bioenergetics, and their environmental responses. Complete genomes of several halphilic archaea (but also halophilic bacteria) have been sequenced in the department. The following organisms are in the main focus:

Halobacterium salinarum

A halophilic archaeon that lives in environments containing salt concentrations of up to 25% (ca. 4 M). It is found in salt lakes and other salinas.

Natronomonas pharaonis

Natronomonas does not only have to cope with two extremes: it lives in highly alkaline lakes which have pH values up to pH 11 in addition to being extremely salty

Haloquadratum walsbyi

(cooperation with Dr. H. Bolhuis, University of Groningen, The Netherlands and Prof. F. Rodríguez-Valera, Uníversidad Miguel Hernández, Alicante, Spain)
This organism is fascenating by its perferctly square morphology in combination with its extreme flatness. It was first described by A. Walsby in 1980 but withstood cultivation for over 25 years.
Haloquadratum is able to live at the limits of water activity, facing salt-saturated solutions with in addition have 2M magnesium chloride. High concentrations of this hygroscopic salt reduce the water activity so that Haloquadratum, although living in an aqueous surrounding, suffers dryness as found in deserts.

The department also works on halophilic eubacteria

Halorhodospira halophila (formerly Ectothiorhodospira halophila)

A halophilic eubacterium that secretes molecular sulfur.

Halobacillus halophilus

(cooperation with Prof. V. Müller, University Frankfurt)
A halophilic eubacterium that requires salt concentration between 0.5 and 2.5 M for growth. It is found in salt marshes, e.g. at the coast of the Northern Sea.

Definition

The term halophile (salt-lover) is generally restricted to those microorganisms that actually require NaCl for growth. The halophiles can further be subdivided into four subclasses depending on their individual range of required salt concentrations.
There are two basic strategies of adaptation to the saline environment

accumulation of up to 5M KCl in the cytoplasm production or accumulation of low-molecular-weight compounds that have osmotic potential, also called compatible osmolytes