Growth and exopolysaccharide yield of Lactobacillus delbrueckii ssp bulgaricus DSM 20081 in batch and continuous bioreactor experiments at constant pH

Some Lactobacillus delbrueckii sap. bulgaricus strains are able to synthesize exopolysaccharides ([PS) and are therefore highly important for the dairy industry as starter cultures. The aim of this study was to investigate the nutritional requirements for growth and EPS production of Lactobacillus delbrueckii ssp. bulgaricus DSM 20081. A medium was developed from a semi-defined medium (SDM) in which glucose was replaced by lactose and different combinations of supplements (nucleobases, vitamins, salts, sodium formate and orotic acid) were added. Constant pH batch fermentation with the modified medium resulted in an [PS yield of approximately 210 mg glucose equivalents per liter medium. This was a 10-fold increase over flask cultivation of this strain in SDM. Although not affecting cell growth, the mixture of salts enhanced the EPS synthesis. Whereas [PS production was approximately 12 mg/g dry biomass without salt supplementation, a significantly higher yield (approximately 20 mg/g dry biomass) was observed after adding the salt mixture. In continuous fermentation, a maximal EPS concentration was obtained at a dilution rate of 0.3 1/h (80 mg EPS/L), which corresponded to a specific EPS production 01 49 mg/g dry biomass. (C) 2011, The Society for Biotechnology, Japan. All rights reserved.