Abstract
Fibrobacter succinogenes is a major rumen fibrolytic bacterium found in high numbers when ruminants are fed cellulose-rich diets. It produces a very efficient fibrolytic system comprising numerous enzymes, but the organization and catalytic features of this system remain unclear. We were using nuclear magnetic resonance (NMR) to study carbohydrate metabolism by Fibrobacter spp. well before the term ‘metabolomics’ was coined. We first analyzed in detail the NMR spectra arising from resting cells of F. succinogenes provided with glucose, cellobiose or cellulose as a substrate. We were able to show carbohydrate cycling and reversibility of some steps. The use of 1D and 2D 1H and 13C NMR showed the synthesis by the cells of unexpected oligosaccharides: maltodextrins, maltodextrin-1-phosphate, and other glucose derivatives. We also showed that maltodextrins and maltodextrins-1-phosphate were synthesized and excreted out of the cell, and could originate from exogenous sugars or endogenous glycogen. According to the substrate and the physiological state of the bacterium (resting or growing cells), metabolic deviations toward the synthesis of these oligosaccharides were observed. We have also used liquid- and solid-state NMR to monitor wheat straw degradation by F. succinogenes. The originality of this NMR approach was to investigate the activity of an entire fibrolytic system on an intact complex substrate (wheat straw). No preferential degradation of amorphous versus crystalline cellulose was observed, nor of cellulose versus hemicelluloses. We showed for the first time a sequential activity of some enzymes of F. succinogenes S85 on wheat straw. In conclusion, our studies illustrate the utility of various NMR approaches to study and better understand sugar and polysaccharide metabolism in rumen bacteria.