Selection of an adhesive phenotype of Streptococcus salivarius subsp. thermophilus for use in fixed-bed reactors

Streptococcus salivarius subsp. thermophilus was cultivated in a chemostat in order to obtain an adhesive phenotype of this strain. When the system was operated at low dilution rates (D < 0.2 h-1) for about 4 weeks, the strain formed a visible film on the surface of the culture vessel. The biofilm cells were not washed out even when dilution rates were increased (D = 6.9 h-1), and this resulted in a high biomass productivity (P = 4.1 g1(-1) h-1). On the other hand, when the culture was grown at dilution rates faster than 0.2 h-1, only the free suspended cells were present in the culture broth, and were washed out at velocities of about 1.0 h-1. The biomass productivity was consequently lower (P = 1.33 g1(-1) h-1) than in the previous case. The selected adhesive phenotype was grown on different glass beads and the possibility of lactate fermentation in a continuous and semicontinuous mode was demonstrated.