Futile cycling of glycogen in Fibrobacter succinogenes as shown by in situ¹H‐NMR and ¹³C‐NMR investigation

Abstract

Glycogen was synthesized during all the growth phases in the rumen anaerobic cellulolytic bacterium Fibrobacter succinogenes. Glycogen synthesis and degradation were monitored using in situ 13C and 'H-NMR spectroscopy in resting cells of F. succinogenes. The cells were incubated at 37°C under anaerobic conditions with [l-13C]glucose and [2-'3C]glucose. 'H-NMR spectra were used to quantify enrichment by ' 3C of metabolism products. Glucose was utilized for energy requirements of the bacterium, essentially via the Embden-Meyerhof pathway, leading to the synthesis of succinate and acetate, while glycogen was stored. From [l-'3C]glucose, labeling occurred on C2 of succinate and acetate, and on both C1 and C6 of glycogen, the labeling on C1 being predominant. The C6-labeling of glycogen may be explained by scrambling and reversal of the glycolytic pathway at the triose-phosphate and fructose 1,6-bisphosphate level. When the bacteria were incubated first with [l-13C]glucose, then washed and incubated with [2-'3C]glucose, the pattern of 13C labeling in the products of the metabolism, as shown by 13C and 'H-NMR spectra, indicated that glycogen was degraded at the same time as it was being stored, suggesting futile cycling of glycogen. The hydrolysis of previously stored glycogen can provide, in the presence of glucose, up to 30% of the carbon source for the bacteria.

Flux Analysis of the Metabolism of Clostridium cellulolyticum Grown in Cellulose-Fed Continuous Culture on a Chemically Defined Medium under Ammonium-Limited Conditions

“…Previous investigations with C. cellulolyticum suggested that the glycogen turnover was involved in carbon flow regulation (5,10). Such observations could be compared with those on F. succinogenes, where glycogen turnover was observed with both cellobiose and cellulose (2,8) and where study of the interaction of carbon and nitrogen metabolisms indicated that addition of ammonium to resting cells of F. succinogenes decreased the flux through glycogen biosynthesis (17).…”

Separation of outer and cytoplasmic membranes of Fibrobacter succinogenes and membrane and glycogen granule locations of glycanases and cellobiase

“…Recently, Gaudet et al (22) reported that synthesis and turnover of glycogen occurred simultaneously in F. succinogenes S85 when cells were grown with glucose as the carbon source, implying a continuous involvement of glycogen in the carbon metabolism. In other bacteria, such as Methylococcus NCIB 11083, stored glycogen has been reported to serve as a carbon and energy source to maintain viability during carbon starvation (42,53).…”

Genetic and physiological characterization of a Rhizobium etli mutant strain unable to synthesize poly-beta-hydroxybutyrate

“…It has been reported that in some bacteria, glycogen, like PHB (15), is continuously being turned over (10), and this may explain how the carbon of PHB can be easily shuffled to the synthesis of another polymer such as glycogen. Therefore, the synthesis and degradation of the so-called reserve polymers have to be integrated into the basic cell metabolism.…”