INACTIVATION OF THE GENE ENCODING SURFACE PROTEIN SSPA IN STREPTOCOCCUS-GORDONII DL1 AFFECTS CELL-INTERACTIONS WITH HUMAN SALIVARY AGGLUTININ AND ORAL ACTINOMYCES

Cell surface protein SSP-5 in the oral bacterium Streptococcus gordoni i M5 binds human salivary agglutinin in a Ca2+-dependent reaction (D. R. Demuth, E. E. Golub, and D. Malamud, J. Biol. Chem. 265:7120-7126, 1990). The region of the gene encoding an N-terminal segment of a rela ted polypeptide (SspA) in S. gordonii DL1 (Challis) was isolated follo wing polymerase chain reaction amplification of genomic DNA. The sspA gene in S. gordonii DL1 was insertionally inactivated by homologous re combination of the erythromycin resistance (Em(r)) determinant ermAM o nto the streptococcal chromosome. The SspA polypeptide (apparent molec ular mass, 210 kDa) was detected on Western blots (immunoblots) of sph eroplast extracts and extracellular culture medium proteins from wild- type strain DL1 but was absent from Em(r) mutants. One SspA- mutant (d esignated OB220) was not altered in rate or extent of aggregation by w hole saliva or parotid saliva but showed reduced aggregation in the pr esence of purified salivary agglutinin. Mutant bacteria were unaffecte d in their ability to adhere to hydroxylapatite beads coated with whol e or parotid saliva and were unaltered in cell surface hydrophobicity. However, the SspA- strain OB220 was deficient in binding salivary agg lutinin and in binding to six strains of Actinomyces naeslundii. There fore, expression of SspA polypeptide in S. gordonii is associated with both agglutinin-dependent and agglutinin-independent aggregation and adherence reactions of streptococcal cells.