The physiological response of C. glutamicum to hyperosmotic stress is investigated by using a combination of biochemical, molecular and biotechnological techniques. We have characterized five uptake systems (BetP, EctP, ProP, LcoP, PutP) and biosynthetic pathways (proline, trehalose) of compatible solutes, which are involved in the adaptation to hyperosmotic stress.
The characterization of wild type and deletion mutants revealed that the uptake of betaine, ectoine and proline is preferred over the synthesis of trehalose or proline. The systems are redundant, since the loss of either all uptake systems or of the biosynthetic pathway for trehalose or proline has no significant influence on the viability of the cells upon osmotic stress.
Expression profiling with respect to osmodependent genes (RNA hybridization, Northern hybridization, RT-PCR, RACE) and of the global response to osmotic stress are under investigation to obtain a better understanding of the signal transduction cascade related to osmotic challenge.
Two corynebacterial carriers, BetP and EctP, are mainly respon-sible for the uptake of betaine after a hyperosmotic shock. Both are regulated on the level of activity and in each case the hydrophilic N- and C-terminal domains of these transporters are involved in activity regulation. BetP is shown to comprise also osmosensing and osmoregulatory functions beside its catalytic (transport) activity. The biochemical properties of the purified carriers BetP and EctP as well as of their hydrophilic extensions, are characterized by using functional reconstitution in proteoliposomes, transport measurements and spectroscopic methods like CD or surface plasmon resonance (IAsys). The combination of activity data (sensing properties) and spectroscopy (structural data) is used to obtain more information on osmosensing.

• DEGUSSA AG
• Deutsche Forschungsgemeinschaft (Schwerpunkt 1070)
• Max-Planck Research School (MPI f. Züchtungsforschung)

• Prof. E. Agosin, Universidad de Santiago, Chile
• Prof. K. Altendorf, PD Dr. K. Jung, Universität Osnabrück
• Prof. E. Bremer, Universität Marburg
• Prof. R. Benz, Universität Würzburg
• Prof. M. Bott, Forschungszentrum Jülich
• Prof. M. Daffe, Institut de Pharmacologie et de Biologie Structurale, Frankreich
• Dr. T. Gensch, Forschungszentrum Jülich
• Dr. J. Kunte, Universität Bonn
• Prof. J. Wood, University of Guelph (Kanada)
• Dr. C. Ziegler, Prof. W. Kühlbrandt, MPI f. Biophysik, Frankfurt

• Wolf, A., Krämer, R. and S. Morbach (2003) Three different pathways for trehalose metabolism in Corynebacterium glutamicum and their significance in response to osmotic stress . Mol. Microbiol. in press
  
  
• Rönsch, H., Krämer, R. and S. Morbach (2003) Impact of osmotic stress on volume regulation, cytoplasmic solute composition and lysine production in Corynebacterium glutamicum MH20-22B. J. Biotechnol. in press



• Nottebrock, D., Meyer, U., Krämer, R. and S. Morbach (2003) Molecular and biochemical characterization of mechanosensitive channels in Corynebacterium glutamicum. FEMS Letters, 218(2):305-309
  [Abstract]



• Morbach S. and R. Krämer (2002) Body shaping under water stress: Osmosensing and osmoregulation of solute transport in bacteria. Chembiochem 3(5): 384-397
  [Abstract]



• Rübenhagen R, Morbach S, Krämer R (2001). The osmoreactive betaine carrier BetP from Corynebacterium glutamicum is a sensor for cytoplasmic K⁺. EMBO J. 20, 5412-5420.
  [Abstract]



• Rübenhagen R, Rönsch H, Jung H, Krämer R, Morbach S, (2000). Osmosensor and osmoregulator properties of the betaine carrier BetP from Corynebacterium glutamicum in proteoliposomes. J. Biol. Chem. 275, 735-741.
  [Abstract]


• Peter H, Weil B, Burkovski A, Krämer R, Morbach S, (1998). Corynebacterium glutamicum is equipped with four secondary carriers for compatible solutes: identification, sequencing and characterization of ProP and EctP. J. Bacteriol. 180, 6005-6012.
  [Abstract]



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