Evidence for recombination between a sialidase (nanH) ofActinomyces naeslundiiandActinomyces oris, previously named ‘Actinomyces naeslundiigenospecies 1 and 2’

Abstract

Actinomyces spp., predominant members of human oral biofilms, may use extracellular sialidase to promote adhesion, deglycosylate immunoglobulins and liberation of nutrients. Partial nanH gene sequences (1077 bp) from Actinomyces oris (n =74), Actinomyces naeslundii (n =30), Actinomyces viscosus (n =1) and Actinomyces johnsonii (n =2) which included the active-site region and the bacterial neuraminidase repeats (BNRs) were compared. The sequences were aligned and each species formed a distinct cluster with five isolates having intermediate positions. These five isolates (two A. oris and three A. naeslundii) exhibited interspecies recombination. The nonsynonymous/synonymous ratio was <1 for both A. oris and A. naeslundii indicating that nanH in both species is under stabilizing selective pressure; nonsynonymous mutations are not selected. However, for A. oris significant negative values in tests for neutral selection suggested the rate of mutation in A. oris was greater than in A. naeslundii but with selection against nonsynonymous mutations. This was supported by the observation that the frequency of polymorphic sites in A. oris, which were monomorphic in A. naeslundii was significantly greater than the frequency of polymorphic sites in A. naeslundii which were monomorphic in A. oris (χ2=7.011; P =0.00081). The higher proportions of A. oris in the oral biofilm might be explained by the higher mutation rate facilitating an increased ability to respond successfully to environmental stress.

Pathogenicity of exopolysaccharide‐producing Actinomyces oris isolated from an apical abscess lesion

“…, Do et al . ). The importance of A. oris type 2 fimbriae, which possess the lectin‐like activity, in biofilm formation and co‐aggregation has been vigorously studied (Yeung , Mishra et al .…”

“…, Do et al . ) and mediate the adhesion of the bacteria to host tissues by exposing the galactose residues of glycoprotein glycans that are present on mucosal surfaces (Ruhl et al . , Do et al .…”

“…The complete function of sialidase of this organism is not fully understood. Recent studies suggested that this enzyme could provide nutrients to the cells by liberating sialic acid from glycans (Paddick et al 2005, Do et al 2008 and mediate the adhesion of the bacteria to host tissues by exposing the galactose residues of glycoprotein glycans that are present on mucosal surfaces (Ruhl et al 2000, Do et al 2008. The importance of A. oris type 2 fimbriae, which possess the lectin-like activity, in biofilm formation and co-aggregation has been vigorously studied (Yeung 1999, Mishra et al 2010.…”

Glycan recognition at the saliva – oral microbiome interface

“…NanH is an interesting sialidase expressed by T. forsythia and several species of Actinomyces [160, 161, 205]. The NanH enzyme is believed to play a role in bacterial attachment to human epithelial cells.…”

The Actinomyces oris type 2 fimbrial shaft FimA mediates co‐aggregation with oral streptococci, adherence to red blood cells and biofilm development

“…The development of this community begins with the initial adherence and colonization of the tooth surface by the so‐called pioneer bacteria, mostly oral streptococci and Actinomyces species, which form an adhesive platform to promote the colonization of bridging bacteria, which in turn attract the late colonizers of the biofilm (Rickard et al ., 2003; Kolenbrander et al ., 2006). Actinomyces oris , formerly Actinomyces naeslundii genospecies 2 (Do et al ., 2008; Henssge et al ., 2009), is the predominant organism among many Actinomyces spp. known to colonize the human oral cavity in all age groups (Kamma et al ., 2000; Preza et al ., 2008; Papaioannou et al ., 2009).…”