Carbohydrate cycling in micro-organisms: what can 13 C-NMR tell us?

Abstract

The extension of (13)C-nuclear magnetic resonance (NMR) techniquesto study cellular metabolism over recent years has provided valuabledata supporting the occurrence, diversity and extent of carbon cyclingin the carbohydrate metabolism of micro-organisms. The occurrenceof such cycles, resulting from the simultaneous operation of differentand sometimes opposite individual steps, is inherently related tothe network organisation of cellular metabolism. These cycles aretentatively classified here as 'reversibility', 'metabolic' and 'substrate'cycles on the basis of their balance in carbon and cofactors. Currenthypotheses concerning the physiological relevance of carbohydratecycles are discussed in light of the (13)C-NMR data. They most likelyrepresent system-level mechanisms for coherent and timely partitioningof carbon resources to fit with the various biosynthetic, energeticor redox needs of cells and/or additional strategies in the adaptivecapacity of micro-organisms to face variation in environmental conditions.