Carbohydrate metabolism in Fibrobacter succinogenes: What NMR tells us

Figures & data

Figure 1.  Pathways of formation of succinate and acetate from [1-¹³C]glucose in F. succinogenes. The position of the ¹³C-label in the ¹³C-enriched metabolite formed with [1-¹³C]glucose as substrate is shown by an asterisk. Reversions and glycogen cycling are indicated by double arrows.

Figure 2.  F. succinogenes cells grown on glucose (A) or cellulose (B). Thin sections of cells examined by transmission electron microscopy after specific polysaccharide staining. Bars represent 0.5 µm.

Figure 3.  Spectra of in vivo kinetics of [1-¹³C]glucose utilization by resting cells of F. succinogenes S85. During the kinetics, signals of ¹³C-glucose (α and β anomers) decrease, while those of the formed metabolites (succinate, acetate, glycogen) increase. Note that glycogen is labeled on both the C1 and C6 positions.

Figure 4.  ¹H NMR spectrum of resting cells of F. succinogenes S85 metabolizing [1-¹³C]glucose. Signals due to protons attached to C2 of acetate and succinate are shown on the spectrum. Those attached to ¹²C are present in the centre of multiplets, while ¹³C-linked proton signals are split with a one bond coupling constant ¹J_13C-1H giving rise to ¹³C satellites, allowing quantification of the ¹³C/¹²C ratios.

Figure 5.  Hypothetical model for the synthesis and metabolism of maltodextrins in F. succinogenes. Maltose (M2) can enter the cells but is not metabolized further; maltotriose (M3) is not a substrate for the bacterium but is a building block for the intracellular synthesis of maltodextrins from M4 to M6 by an enzyme similar to MalQ. Maltodextrins can be excreted. Glycogen is degraded by a combination of a putative glycogen phosphorylase (GlgP, generating G-1P) and a glycogen-debranching enzyme (GlgX) that lead to maltotetraose (M4). The maltodextrin phosphorylase MalP produces M3 and G-1P from the maltodextrins.

Figure 6.  Solid-state NMR monitoring of straw degradation by F. succinogenes. ¹³C CP-MAS NMR spectra recorded after 8 h, 16 h, and 1, 2, 3, and 4 days of F. succinogenes growth. C1, C3, C4, C5, and C6 correspond to the different carbons of sugar units of cellulose and hemicelluloses. k, crystalline cellulose; nk, amorphous cellulose; OMe, CH3 of methyl ester group.