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Characterization of the Erwinia chrysanthemi gan Locus, Involved in Galactan Catabolism ^,

Unité de Glycobiologie Structurale et Fonctionnelle, UMR USTL-CNRS 8576 IFR147, Université des Sciences et Technologies de Lille, Bâtiment C9, 59655 Villeneuve d'Ascq Cedex, France,¹ Microbiologie, Adaptation et Pathogénie UMR 5240 CNRS, Université Lyon 1, INSA-Lyon, Université de Lyon, Domaine Scientifique de la Doua, Bâtiment André Lwoff, 10 Rue Raphaël Dubois, 69622 Villeurbanne Cedex, France²

Received 31 May 2007/ Accepted 12 July 2007

ß-1,4-Galactan is a major component of the ramified regions of pectin. Analysis of the genome of the plant pathogenic bacteria Erwinia chrysanthemi revealed the presence of a cluster of eight genes encoding proteins potentially involved in galactan utilization. The predicted transport system would comprise a specific porin GanL and an ABC transporter made of four proteins, GanFGK₂. Degradation of galactans would be catalyzed by the periplasmic 1,4-ß-endogalactanase GanA, which released oligogalactans from trimer to hexamer. After their transport through the inner membrane, oligogalactans would be degraded into galactose by the cytoplasmic 1,4-ß-exogalactanase GanB. Mutants affected for the porin or endogalactanase were unable to grow on galactans, but they grew on galactose and on a mixture of galactotriose, galactotetraose, galactopentaose, and galactohexaose. Mutants affected for the periplasmic galactan binding protein, the transporter ATPase, or the exogalactanase were only able to grow on galactose. Thus, the phenotypes of these mutants confirmed the functionality of the gan locus in transport and catabolism of galactans. These mutations did not affect the virulence of E. chrysanthemi on chicory leaves, potato tubers, or Saintpaulia ionantha, suggesting an accessory role of galactan utilization in the bacterial pathogeny.

Published ahead of print on 20 July 2007.

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