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Journal of Bacteriology, November 1998, p. 6005-6012, Vol. 180, No. 22
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Corynebacterium glutamicum Is Equipped with Four Secondary Carriers for Compatible Solutes: Identification, Sequencing, and Characterization of the Proline/Ectoine Uptake System, ProP, and the Ectoine/Proline/Glycine Betaine Carrier, EctP

Heidi Peter,1 Brita Weil,1 Andreas Burkovski,2 Reinhard Krämer,2,* and Susanne Morbach2

Institut für Biotechnologie 1, Forschungszentrum Jülich GmbH, D-52425 Jülich,1 and Institut für Biochemie der Universität zu Köln, D-50764 Cologne,2 Germany

Received 6 July 1998/Accepted 14 September 1998

Gram-positive soil bacterium Corynebacterium glutamicum uses the compatible solutes glycine betaine, proline, and ectoine for protection against hyperosmotic shock. Osmoregulated glycine betaine carrier BetP and proline permease PutP have been previously characterized; we have identified and characterized two additional osmoregulated secondary transporters for compatible solutes in C. glutamicum, namely, the proline/ectoine carrier, ProP, and the ectoine/glycine betaine/proline carrier, EctP. A Delta betP Delta putP Delta proP Delta ectP mutant was unable to respond to hyperosmotic stress, indicating that no additional uptake system for these compatible solutes is present. Osmoregulated ProP consists of 504 residues and preferred proline (Km, 48 µM) to ectoine (Km, 132 µM). The proP gene could not be expressed from its own promoter in C. glutamicum; however, expression was observed in Escherichia coli. ProP belongs to the major facilitator superfamily, whereas EctP, together with the betaine carrier, BetP, is a member of a newly established subfamily of the sodium/solute symporter superfamily. The constitutively expressed ectP codes for a 615-residue transporter. EctP preferred ectoine (Km, 63 µM) to betaine (Km, 333 µM) and proline (Km, 1,200 µM). Its activity was regulated by the external osmolality. The related betaine transporter, BetP, could be activated directly by altering the membrane state with local anesthetics, but this was not the case for EctP. Furthermore, the onset of osmotic activation was virtually instantaneous for BetP, whereas it took about 10 s for EctP.

* Corresponding author. Mailing address: Institut für Biochemie der Universität zu Köln, Zülpicher Str. 47, D-50674 Cologne, Germany. Phone: 49 221 470 6461. Fax: 49 221 470 5091. E-mail: r.kraemer{at}uni-koeln.de.

Journal of Bacteriology, November 1998, p. 6005-6012, Vol. 180, No. 22
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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