Uncultivated clones BU045 and BU063 and Tannerella forsythia, a 'consensus periodontal pathogen', are the closest known relatives within the genus Tannerella. They have been described to inhabit different ecological niches of the human oral cavity. In this study, fluorescent in situ hybridization (FISH) and immunofluorescence were combined to investigate the prevalence and abundance of BU045 and BU063 in comparison to T. forsythia in plaques from gingivitis, necrotizing ulcerative gingivitis (NUG) and chronic periodontitis. Phylotype-specific FISH probes identified BU045 and BU063 as elongated thin rods with a segmented structure. Two structurally similar and previously unknown, rare phylotypes (127 + and 997 + ) were also identified due to partial 16S rRNA sequence identity with T. forsythia. In gingivitis, NUG and periodontitis patients, BU045, BU063, 127 + , 997 + and T. forsythia were detected with prevalences of 50/83/71/14 and 81 %, 100/100/86/17 and 53 %, and 100/100/12/0 and 100 %, respectively. Supragingivally, colonization density of all five organisms was generally low, rarely exceeding 0.1 % of the total biota. In periodontal pocket samples, however, cell numbers of T. forsythia, but not of the uncultivable phylotypes, were greatly elevated. Our data demonstrate that Tannerella phylotypes BU045, BU063, 127 + and 997 + consist of long slim rods with segments, which, with respect to FISH stainability, often behaved as independent units. The phylotypes are frequent but low-level colonizers of various periodontal disease-associated plaques. Their apparent inability to proliferate to high density seems to exclude any relevance for the pathogenesis of periodontal diseases.
INTRODUCTIONRelying on comprehensive culture analyses, Moore & Moore (1994) estimated that, on a population basis, the human oral cavity might harbour some 500 bacterial species. With the emergence of culture-independent methods for the identification of microbial biota (see Amann et al., 1995 for a review) it became clear that probably less than 50 % of the oral taxa have been cultured so far (Wilson et al., 1997). During the last decade hundreds of previously unknown phylotypes and clones have been identified in studies investigating 16S rRNA diversity in different forms of dental plaque (Paster et al., 2001(Paster et al., , 2002Munson et al., 2004;Aas et al., 2005;Kumar et al., 2005;de Lillo et al., 2006). Among the many uncultivable human oral phylotypes two clones with an apparently supragingival habitat, BU045 and BU063, attracted some interest, because their 16S rRNA gene sequence groups them within the genus Tannerella (Paster et al., 2001;Leys et al., 2002;de Lillo et al., 2004), which otherwise contains, besides some uncultivated clones from soil, only a single species, Tannerella forsythia (also known as Tannerella forsythensis) (Tanner et al., 1986;Tanner & Izard, 2006). T. forsythia is a 'consensus periodontal pathogen ' (Haffajee & Socransky, 2006) and associated with subgingival plaque from chronic and occasionally aggress...