Actinomyces serovar WVA963 coaggregation-defective mutant strain PK2407 secretes lactose-sensitive adhesin that binds to coaggregation partner Streptococcus oralis 34.

Actinomyces serovar WVA963 strain PK1259 mediates intergeneric coaggregation with several oral streptococci. These lactose-inhibitable coaggregations appear to involve a 95-kDa putative actinomyces adhesin in complex with type 2 fimbriae. A coaggregation-defective strain PK2407 lacking type 2 fimbriae synthesizes the putative adhesin but appears unable to present it properly on its surface. Antiserum was raised against surface sonicates of PK2407 and was absorbed with a different coaggregation-defective mutant PK3092 that synthesizes type 2 fimbriae but no adhesin. This absorbed antiserum specifically blocked lactose-inhibitable coaggregation of wild-type strain PK1259 and Streptococcus oralis 34 and identified a 95-kDa protein in ammonium sulfate precipitates of culture supernatant of the coaggregation-defective mutant PK2407. The 95-kDa secreted protein was bound to the streptococcal partner cells and to lactose-agarose affinity beads and was released by lactose from both the affinity beads and partner, indicating that the secreted and precipitated protein is biochemically active and may mediate coaggregation with streptococci.

comYA, a gene similar to comGA of Bacillus subtilis, is essential for competence-factor-dependent DNA transformation in Streptococcus gordonii.

Tn4001 mutagenesis identified a new competence gene in Streptococcus gordonii Challis designated comYA. A comYA mutant was completely deficient in transformation and exhibited decreased levels of DNA binding and hydrolysis. The deduced 319-amino-acid ComYA protein exhibited 57% similarity and 33% identity to the ComGA transporter protein of Bacillus subtilis and contained the Walker A-box motif conserved in ATP-binding proteins as well as aspartic acid boxes Asp-1 and Asp-2 present in some components of the general secretory pathway of gram-negative bacteria. comYA appeared to be part of a putative operon encompassing a comGB homolog, designated comYB, together with sequences that could encode ComGC- and ComGD-like peptides designated ComYC and ComYD, respectively, as well as other components. The putative ComYC and ComYD peptides had leader sequences similar to the type IV N-methylphenylalanine pilins of gram-negative bacteria, but unlike other examples in this class, including B. subtilis, they contained an alanine at position -1 of the leader instead of the usual glycine residue. Northern analysis identified a single 6.0-kb comYA-containing transcript strictly dependent on exogenous competence factor for expression in ComA1 cells. An identical pattern of expression was seen in wild-type Challis cells grown under conditions of maximal competence but not in cells that were noncompetent.