Effects of complete cell recycling on product formation byLactobacillus casei ssp.rhamnosus in continuous cultures

The lactic acid bacteriumLactobacillus casei ssprhamnosus was cultivated in a system with complete cell recycling in order to obtain information on how this cultivation technique affected the microorganisms. Cultivations at two different glucose concentrations (25 g/L and 50 g/L) were performed. Hollow fiber filters were used for separating the cells from the spent broth. The cell recycling was carried out for 128–135 h. Samples were taken three to four times daily for analysis ofd- andl-lactate, glucose concentration, and cell mass. Protein patterns were studied with two-dimensional electrophoresis. A change in the protein pattern was observed. Dry weight of cell mass of 86 g/L was obtained when cultivated on 50 g glucose/L, which was approximately 15 times more than in the batch culture. The percentage ofd-lactate of the total lactate increased with time; when cultivated on 25 g glucose/L, it increased from 3% to 13%. No racemase was detected by the methods used. The data collected from these two recycling experiments show that this is an efficient way to obtain high cell densities, but that the method can affect the product formation pattern of the microorganism.