Funktion und Regulation mechanosensitiver Efflux-Systeme für kompatible Solute in Corynebacterium glutamicum

Ruffert, S.

Dissertation / PhD Thesis/Book

Funktion und Regulation mechanosensitiver Efflux-Systeme für kompatible Solute in Corynebacterium glutamicum

Ruffert, S. (Corresponding author)FZJ*

1999
Forschungszentrum, Zentralbibliothek Jülich

Jülich : Forschungszentrum, Zentralbibliothek, Berichte des Forschungszentrums Jülich 3621, (1999) = Köln, Univ., Diss., 1999

Please use a persistent id in citations: http://hdl.handle.net/2128/4424

Report No.: Juel-3621

Abstract: Under conditions of low osmolality cells are exposed to massive water influx. In response to sudden hypoosmotic stress, the gram positive soil bacterium Corynebacterium glutamicum releases low-molecular-mass solutes to maintain constant turgor pressure. The systems that mediate the efflux process have been studied. Upon osmotic downshock, the cells preferentially released compatible solutes such as glycine betaine and proline. Release of lysine and glutamate was restricted and ATP was totally retained. The cells maintained relative high cytoplasmic potassium concentrations. Several results suggest that the efflux is channel mediated. First, the efflux was extremely fast reaching an efflux rate of 6000 tJmol· min-1 . 9 dm-1 or higher. Second, efflux was insensitive to the addition of external substrate. It was also unchanged after uncoupling by eeep. A continuous decrease of external osmolarity leads to a continuous efflux of compounds. This also effects the energetic situation of the cells. The existence of mechanosensitive channels in the cytoplasmic membranes of e.glutamicum could be demonstrated using patch-clamp techniques. Fragments of the plasma membrane were fused into giant liposomes. Application of suction in the pipette revealed the presence of two types of high conductance mechanosensitive channels that were voltage-independent and could be inhibited by gadolinium. 80th channels were characterized by their slow kinetics, their weak cationic selectivity, and differed only by their conductance (600-700 pS and 1200-1300 pS in 0.1 M KcI), raising the possibility that they might correspond to different oligomers of the same subunit. Since their discovery in bacteria it has been proposed that mechanosensitive channels play a physiological role in sensing and/or adapting to changing osmotic environments. The involvment of these channels in the shock-induced release of compatible solutes in e.glutamicum is discussed

Classification: