Surface Expression of the Conserved C Repeat Region of Streptococcal M6 Protein within the Pip Bacteriophage Receptor ofLactococcus lactis

Open Access
Publisher Website
Google Scholar
Abstract
The C repeat region of the M6 protein (M6c) fromStreptococcus pyogeneswas expressed within the Pip bacteriophage receptor on the surface ofLactococcus lactis.M6c was also detected in the culture medium. Thepip-emm6callele was integrated into the chromosome and stably expressed without antibiotic selection. The level of cell-associated surface expression of PipM6c was 0.015% of total cellular protein. The amount of PipM6c on the cell surface was increased about 17-fold by expressingpip-emm6cfrom a high-copy-number plasmid. Replacing the nativepippromoter with stronger promoters isolated previously fromLactobacillus acidophilusincreased surface expression of PipM6c from the high-copy-number plasmid up to 27-fold. Concomitantly, the amount of PipM6c in the medium increased 113-fold. The amount of PipM6c did not vary greatly between exponential- and stationary-phase cultures. Western blots indicated that the full-length PipM6c protein and most of the numerous proteolytic products were found only on the cell surface, whereas only one proteolytic fragment was found in the culture medium.