A recent report by Matarazzo et al. [11] demonstrated the high frequency of Archaea present in healthy shallow gingival sulci. Further

investigations are required to determine whether these represent buy AZD0530 merely transient visitors or colonizers. At present, it is generally thought that Archaea are distributed in sites of periodontitis with deep periodontal pockets, although whether they are involved in the pathogenesis of periodontitis remains a matter of debate. Some recent studies also evaluated the relative abundance of Archaea in the microflora of subgingival plaque. Lepp et al. [15] reported that Archaea were the dominant organisms with a relative abundance of 18.5% among the total prokaryotic populations at severe diseased sites of periodontitis (probing depth ≥6 mm). However, some subsequent studies indicated that the percentages of Archaea in the plaque population were lower than in Lepp’s report, ranging from 0.08% to 0.5% (Table 1). The proportions of hydrogenotrophs were below 1% in most cases [27]. In addition, in the presence of Fe3+ or SO42−, sulfate-reducing bacteria or iron-reducing bacteria have priority for the use of hydrogen. These discrepancies may have been due to methodological differences between the research groups. However, considering the characteristics of subgingival microflora and the fact that methanogenic Archaea are terminal hydrogen consumers, the results

of the latter research are more reasonable than those reported EX 527 chemical structure by Lepp et al. [15]. With regard to the diversity of Archaea, most previous studies indicated that M. oralis and M. oralis-like phylotype

were the dominant archaeal species in subgingival plaque. Compared to the bacterial community, which consists of hundreds of species [27], only several archaeal species have been reported previously in sites of periodontitis ( Table 1). Methanogens www.selleck.co.jp/products/Neratinib(HKI-272).html generally have synergistic relations with other microorganisms in individual natural niches. Unfortunately, the genome of M. oralis has not yet been analyzed, and the details are still unclear. The low diversity indicates that among archaeal species, M. oralis has genetic advantages making it well adapted to the oral anaerobic environment in relation to oral bacterial species. In addition to M. oralis, Thermoplasmata, Methanosarcina, and Methanobacterium spp. have been identified in plaque ( Table 1). Horz et al. [26] identified Thermoplasmatales and M. oralis in the same plaque samples, suggesting that both types of Archaea can coexist in an ecological niche. Further investigation and discussion are required to determine whether the minor archaeal species were transient visitors or inhabitants in the gingival sulci. This question will be answered by quantitative molecular analysis using species-specific primers. A series of studies have also been performed in endodontic infection regarding the distribution and diversity of Archaea (Table 2).