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Team's presentation

Plant cell walls constitute the largest reservoir of carbon on land. They are made of cellulose fibers embedded in a matrix of heterogeneous polysaccharides forming the hemicellulose, and of lignin, a polymer of aromatic components. Their complete biodegradation requires numerous different enzymes and is a key and limiting step in global carbon cycle. Using biochemical and genetic approaches, our group studies how the model anaerobic bacterium Ruminiclostridium cellulolyticum performs the extracellular deconstruction of plant cell walls polysaccharides via multi-enzymatic complexes termed cellulosomes. The group also explores how the bacterium manages the uptake of the generated oligosaccharides through a collection of ABC-transporters, and how their final cytosolic depolymerization is achieved. Using omics approaches, the group investigates how, in absence of oxygen, R. cellulolyticum copes with the lignin to access the polysaccharides. The same omics approaches are also applied to unravel how the various extracellular degradation systems, sugar uptake systems and metabolic pathways are orchestrated during the growth on natural and complex substrates like wheat straw. Other plant cell wall degrading bacteria, recently isolated, are also examined, whereas biotechnological applications targeting the biofuel and commodity chemicals sectors are currently developed.

Team's news

Team projects

AXIS 2

Sensing a highly complex and evolving environment

AXIS 3

Saving energy through transport and an atypical metabolism

Our model bacterium, R. cellulolyticum, and related clostridia are important players of the terrestrial carbon cycle and occupy anaerobic biotopes where plant cell wall polymers accumulate. This carbon source is extremely complex. It is composed of cellulose fibers embedded in a matrix of highly heterogenous polysaccharides forming the hemicellulose, and surrounded by a polymer of aromatic compounds called the lignin. The polysaccharidic part of the plant cell walls is for instance composed of up to 30 different types of monosaccharides and 50 different types of glycosidic linkages. R. cellulolyticum can completely catabolize most of these polysaccharides. The genes encoding the extracellular degrading enzymes (gathered in large complexes called cellulosomes), the intracellular enzymes as well as the ABC-transporters required for the uptake of mono/oligosaccharides generated during the extracellular depolymerization, are generally gathered in large operons. The group currently studies how the expression of the various operons is controlled during the growth on such complex substrate, by the vast repertoire of two- or three-component systems. How does the bacterium coordinate its various degradation and transport systems to continuously adapt to the evolving substrate, is also a central question we currently address in our research. Finally, the way our model bacterium but also two recently isolated anaerobic and cellulolytic bacteria cope with the lignin hurdle (partly degrade, modify?) to access the polysaccharides is also explored.

Our model bacterium R. cellulolyticum can catabolize the cellulose and the major polysaccharides forming the hemicellulose in plant cell walls. These polymers are degraded extracellularly by an arsenal of enzymes gathered in cellulosomes. Nevertheless, this degradation generally does not lead to the release of the elementary monosaccharides composing these polysaccharides, but rather to oligosaccharides which are imported “en bloc” via specific ABC-transporters. For instance, the group has shown that when R. cellulolyticum grows on xyloglucan, this hemicellulosic polysaccharide is degraded extracellularly into xyloglucandextrins which are imported by an ABC-transporter, thus allowing the simultaneous uptake of up to nine monosaccharides at the cost of single ATP. No PTS-system was found in R. cellulolyticum but its genome encodes many other uncharacterized ABC-transporters predicted to import sugars, whose substrate(s) is(are) not yet known. The identification of their ligand(s) will help us to establish a map of sugars that can be potentially taken up and processed by our model bacterium, and create a useful database for microbiologists, as similar ABC-transporters are found in many other Gram-positive bacteria. Are some of these ABC-transporters redundant in terms of substrate? Are they gathered in patches or scattered at the surface of the bacterium? These are some of the questions we also plan to address.

Beyond sugar uptake, the recent studies show that the central carbon metabolism in R. cellulolyticum appears to be unconventional and particularly energy saving. We thus plan to explore further the central carbon metabolism of our model bacterium, and determine whether it is GTP- or ATP-driven. This study may also lead to the discovery of novel metabolic enzymes displaying uncommon traits (like the GTP-dependent and reversible hexokinase) that could inspire novel metabolic engineering applied to bacteria of industrial interest.

The Team

Henri Pierre Fierobe

Group leader / Research director (DR-CNRS)

Séverine Gagnot

Engineer (IE-CNRS)

Chantal Tardif

Professor (PR-AMU)

Nicolas Vita

Researcher (CR-CNRS)

Pascale Dephilip

Assistant professor (MCF-AMU)

Sandrine Pages-Bruno

Assistant professor (MCF-AMU)

Stéphanie Perret

Assistant professor (MCF-AMU)

Hélène David

Engineer (CDD-CNRS)

Nian Liu

PhD student (PhD-AMU)

Scientific publications