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Sci Rep. 2016 Mar 7;6:22770. doi: 10.1038/srep22770.

Mechanisms involved in xyloglucan catabolism by the cellulosome-producing bacterium Ruminiclostridium cellulolyticum.

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Aix-Marseille Université-CNRS, Laboratoire de Chimie Bactérienne, UMR7283, IMM, 31 chemin Joseph Aiguier, F-13402 Marseille, France.
Plate-forme de Protéomique, IMM, 31 chemin Joseph Aiguier, F-13402 Marseille, France.
Aix-Marseille Université-CNRS, Laboratoire d'Architecture et Fonction des Macromolécules Biologiques, UMR7257, Parc Technologique de Luminy, F-13288 Marseille, France.


Xyloglucan, a ubiquitous highly branched plant polysaccharide, was found to be rapidly degraded and metabolized by the cellulosome-producing bacterium Ruminiclostridium cellulolyticum. Our study shows that at least four cellulosomal enzymes displaying either endo- or exoxyloglucanase activities, achieve the extracellular degradation of xyloglucan into 4-glucosyl backbone xyloglucan oligosaccharides. The released oligosaccharides (composed of up to 9 monosaccharides) are subsequently imported by a highly specific ATP-binding cassette transporter (ABC-transporter), the expression of the corresponding genes being strongly induced by xyloglucan. This polysaccharide also triggers the synthesis of cytoplasmic β-galactosidase, α-xylosidase, and β-glucosidase that act sequentially to convert the imported oligosaccharides into galactose, xylose, glucose and unexpectedly cellobiose. Thus R. cellulolyticum has developed an energy-saving strategy to metabolize this hemicellulosic polysaccharide that relies on the action of the extracellular cellulosomes, a highly specialized ABC-transporter, and cytoplasmic enzymes acting in a specific order. This strategy appears to be widespread among cellulosome-producing mesophilic bacteria which display highly similar gene clusters encoding the cytosolic enzymes and the ABC-transporter.

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