Cloning of the Streptococcus gordonii PK488 gene, encoding an adhesin which mediates coaggregation with Actinomyces naeslundii PK606

Abstract

Coaggregation between Streptococcus gordonii PK488 and Actinomyces naeslundii PK606 is mediated by a 38-kDa streptococcal protein, designated ScaA. The gene, scaA, which encodes this protein has been cloned into Escherichia coli. A genomic S. gordonii PK488 library (in Lambda ZAP II) was screened with anti-S. gordonii immunoglobulin G absorbed with S. gordonii PK1804, an isogenic coaggregation-defective mutant of strain PK488. A positive recombinant phage was isolated, and a phagemid designated pRA1 was obtained which contained a 6.6-kb insert. Expression of scaA from pRA1 and from a subcloned internal 2.1-kb fragment was observed. The absorbed antiserum cross-reacted with a 34.7-kDa protein, SsaB, from S. sanguis 12, also a coaggregation partner of A. naeslundii PK606. Absorbed antiserum to S. gordonii PK488 and antiserum to SsaB both reacted with 38-kDa proteins in supernatants from mildly sonicated preparations from 11 other coaggregation partners of A. naeslundii PK606. Putative adhesin genes were identified in each of these coaggregation partners by Southern analysis of their genomic DNA with the cloned 2.1-kb fragment as a probe. A 30-base oligonucleotide probe based on the sequence of ssaB of S. sanguis 12 hybridized in an identical manner. These data extend the notion that most of the viridans streptococci that coaggregate with actinomyces are capable of expressing ScaA-related proteins.