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

Julie Ravachol (1, 2) , Pascale De Philip (1, 2) , Romain Borne (1, 2) , Pascal Mansuelle (2) , Maria J. Maté (3) , Stéphanie Perret (1, 2) , Henri-Pierre Fierobe (1)

1 LCB - Laboratoire de chimie bactérienne
2 IMM - Institut de Microbiologie de la Méditerranée
3 AFMB - Architecture et fonction des macromolécules biologiques

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 beta-galactosidase, alpha-xylosidase, and beta-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.

Domaines: Bactériologie

Julie Ravachol, Pascale De Philip, Romain Borne, Pascal Mansuelle, Maria J. Maté, et al.. Mechanisms involved in xyloglucan catabolism by the cellulosome-producing bacterium Ruminiclostridium cellulolyticum. Scientific Reports, 2016, 6, pp.22770. ⟨10.1038/srep22770⟩. ⟨hal-01440763⟩