Production of curdlan-type polysaccharide by Alcaligenes faecalis in batch and continuous culture

The biosynthesis of a thermogelable, extracellular homo-beta-(1 leads to 3)-glucan called "curdlan," has been studied in batch and continuous cultures of Alcaligenes faecalis var. myxogenes. Curdlan production is associated with the poststationary phase of a nitrogen-depleted, aerobic batch culture. Exopolymer is not detected in single-stage, carbon-limited continuous cultures but curdlan can be isolated from the effluent of a nitrogen-limited chemostat operating at a dilution rate (D) of less than 0.1 h-1. A spontaneous variant of strain ATCC 21680 was isolated and found to be compatible with long-term, nitrogen-limited chemostat culture. The specific rate of curdlan production is approximately four times higher in poststationary batch cultures than in single-stage continuous fermentations. The product yield (Yp/S) associated with batch processing (nongrowing cultures) is approximately 0.5 g curdlan/g glucose, with CO2 being the only detectable by-product.