Recombinant Streptococcus gordonii as live vehicle for vaccine antigens

All recombinant strains, including the parent recombinant S. gordonii GP231 expressing whole M6, do produce in liquid culture the cloned proteins from mid mid exponential phase of growth to the late stationary phase. The maximum protein quantity per cell is detected about one generation after the beginning of the stationary phase (Medaglini et al., 1993). This characteristic enables to collect the bacterial cells for protein analysis and purification purposes at the highest possible cell density. Recombinant proteins are detected in media containing no dextrose (Tryptic Soy Broth without dextrose) and in standard media containing 0.2% of glucose, while the protein quantity diminishes, in stationary phase of growth, when high glucose containing media (1, 2, 5 10% glucose) are used possibly due to proteolytic degradation. On solid media the recombinant proteins are produced and are detectable since the colony becomes visible on the plate and thus making protein detection through colony blot screening possible. Cell fractioning, immunofluorescence and electron microscopy on bacteria grown to late exponential phase did confirm surface display of the M6-based fusion proteins.