Factors affecting utilization of carbohydrates by clostridia

The overriding principle of bacterial metabolism is the utilization of extracellular nutrients to provide building blocks and energy to support cellular growth. Nutrients are (if necessary) degraded by specific extracellular depolymerases, taken into the cell via specific membrane-bound transport systems, and mobilised by specific enzymes, the synthesis and activity of which are controlled in response to the nutritional status of the environment. Saccharolytic clostridia exhibit the capacity to utilise a wide spectrum of carbon sources for growth. Polymers such as starch and cellulose are degraded by a variety of enzymes; the products, and other soluble, low molecular mass substrates, are accumulated by a number of different mechanisms, predominant among which is the phosphoenolpyruvate-dependent carbohydrate phosphotransferase system (PTS). Although not fully characterised, the clostridial PTS has been shown to be functionally related to the PTS in other bacteria. Many catabolic enzyme and transport systems in clostridia have been found to be induced by the substrate and repressed in the presence of a rapidly metabolised sugar such as glucose, but mechanisms responsible for these phenomena have not been identified. Description of these mechanisms will depend on a detailed molecular analysis of catabolic genes and their expression, and is essential to provide a complete understanding of clostridial physiology.