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Journal of Bacteriology, December 2005, p. 8375-8384, Vol. 187, No. 24
0021-9193/05/$08.00+0     doi:10.1128/JB.187.24.8375-8384.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Role of the Pseudomonas fluorescens Alginate Lyase (AlgL) in Clearing the Periplasm of Alginates Not Exported to the Extracellular Environment

Karianne Bakkevig,1 Håvard Sletta,2 Martin Gimmestad,1 Randi Aune,2 Helga Ertesvåg,1 Kristin Degnes,1 Bjørn Erik Christensen,1 Trond E. Ellingsen,2 and Svein Valla1*

Department of Biotechnology, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway,1 SINTEF Materials and Chemistry, Department of Biotechnology, SINTEF, N-7034 Trondheim, Norway2

Received 1 July 2005/ Accepted 13 September 2005

Alginate is an industrially widely used polysaccharide produced by brown seaweeds and as an exopolysaccharide by bacteria belonging to the genera Pseudomonas and Azotobacter. The polymer is composed of the two sugar monomers mannuronic acid and guluronic acid (G), and in all these bacteria the genes encoding 12 of the proteins essential for synthesis of the polymer are clustered in the genome. Interestingly, 1 of the 12 proteins is an alginate lyase (AlgL), which is able to degrade the polymer down to short oligouronides. The reason why this lyase is associated with the biosynthetic complex is not clear, but in this paper we show that the complete lack of AlgL activity in Pseudomonas fluorescens in the presence of high levels of alginate synthesis is toxic to the cells. This toxicity increased with the level of alginate synthesis. Furthermore, alginate synthesis became reduced in the absence of AlgL, and the polymers contained much less G residues than in the wild-type polymer. To explain these results and other data previously reported in the literature, we propose that the main biological function of AlgL is to degrade alginates that fail to become exported out of the cell and thereby become stranded in the periplasmic space. At high levels of alginate synthesis in the absence of AlgL, such stranded polymers may accumulate in the periplasm to such an extent that the integrity of the cell is lost, leading to the observed toxic effects.

* Corresponding author. Mailing address: Department of Biotechnology, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway. Phone: (47)73593320. Fax: (47)73591283. E-mail: svein.valla{at}biotech.ntnu.no.

Journal of Bacteriology, December 2005, p. 8375-8384, Vol. 187, No. 24
0021-9193/05/$08.00+0     doi:10.1128/JB.187.24.8375-8384.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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