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Applied and Environmental Microbiology, August 1999, p. 3304-3311, Vol. 65, No. 8
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Nanomolar Levels of Dimethylsulfoniopropionate, Dimethylsulfonioacetate, and Glycine Betaine Are Sufficient To Confer Osmoprotection to Escherichia coli

Anne Cosquer,1,2,* Vianney Pichereau,2,dagger Jean-Alain Pocard,2 Jacques Minet,1 Michel Cormier,1 and Théophile Bernard2

Laboratoire de Microbiologie Pharmaceutique, Université de Rennes 1, 35043 Rennes,1 and Equipe "Membranes et Osmorégulation," UPRES-A CNRS 6026, Université de Rennes 1, 35042 Rennes,2 France

Received 21 December 1998/Accepted 11 May 1999

We combined the use of low inoculation titers (300 ± 100 CFU/ml) and enumeration of culturable cells to measure the osmoprotective potentialities of dimethylsulfoniopropionate (DMSP), dimethylsulfonioacetate (DMSA), and glycine betaine (GB) for salt-stressed cultures of Escherichia coli. Dilute bacterial cultures were grown with osmoprotectant concentrations that encompassed the nanomolar levels of GB and DMSP found in nature and the millimolar levels of osmoprotectants used in standard laboratory osmoprotection bioassays. Nanomolar concentrations of DMSA, DMSP, and GB were sufficient to enhance the salinity tolerance of E. coli cells expressing only the ProU high-affinity general osmoporter. In contrast, nanomolar levels of osmoprotectants were ineffective with a mutant strain (GM50) that expressed only the low-affinity ProP osmoporter. Transport studies showed that DMSA and DMSP, like GB, were taken up via both ProU and ProP. Moreover, ProU displayed higher affinities for the three osmoprotectants than ProP displayed, and ProP, like ProU, displayed much higher affinities for GB and DMSA than for DMSP. Interestingly, ProP did not operate at substrate concentrations of 200 nM or less, whereas ProU operated at concentrations ranging from 1 nM to millimolar levels. Consequently, proU+ strains of E. coli, but not the proP+ strain GM50, could also scavenge nanomolar levels of GB, DMSA, and DMSP from oligotrophic seawater. The physiological and ecological implications of these observations are discussed.

* Corresponding author. Mailing address: Equipe "Membranes et Osmorégulation," UPRES-A CNRS 6026, Université de Rennes 1, Campus de Beaulieu, Avenue du Général Leclerc, 35042 Rennes, France. Phone and fax: 33 (0) 2 99 28 61 40. E-mail: pocard{at}univ-rennes1.fr.

dagger Present address: Laboratoire de Microbiologie de l'Environnement, IRBA, Université de Caen, 14032 Caen, France.

Applied and Environmental Microbiology, August 1999, p. 3304-3311, Vol. 65, No. 8
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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