The xylan utilization system of Xanthomonas campestris controls epiphytic life and reveals common features with animal gut symbionts
M. ARLAT (1), G. Déjean (1), S. Blanvillain (1), E. Lauber (2). (1) INRA/CNRS University Toulouse 3, Castanet Tolosan, France; (2) INRA/CNRS, Castanet Tolosan, France
TonB-dependent receptors (TBDTs) are outer membrane proteins mainly known for the active transport of iron siderophore complexes in Gram-negative bacteria. Analysis of the genome of <i>Xanthomonas</i> species revealed an overrepresentation of these transporters. This overrepresentation is associated with the ability to exploit plant carbohydrate and we proposed the existence of specific carbohydrate utilisation systems with TBDTs (named CUT systems). Recently, we identified a CUT system involved in the utilisation of xylan, a major component of plant cell wall and the second most abundant plant polysaccharide in nature. This CUT system encompasses genes required for the degradation of xylan as well as genes for the transport and metabolism of xylo-oligosaccharides, xylose and glucuronate. Interestingly, these genes which expression is induced by xylo-oligosaccharides, are required for optimal growth on plant leaves. Part of the xylanolytic machinery of <i>Xanthomonas</i>, including TBDT genes, displays a high degree of conservation with the xylose-regulon of the oligotrophic aquatic bacterium <i>Caulobacter crescentus</i>. Moreover, it shares common features, including the presence of TBDTs, with the xylan utilisation systems of <i>Bacteroides ovatus</i> and <i>Prevotella bryantii</i>, two gut symbionts. These similarities and our results support an important role for TBDTs and xylan utilisation systems for bacterial adaptation in the phyllosphere, oligotrophic environments and animal guts.
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