Abstract
Methanogens are acknowledged archaeal members of modern dental calculus microbiota and dental pathogen complexes. Their repertoire in ancient dental calculus is poorly known. We therefore investigated archaea in one hundred dental calculus specimens collected from individuals recovered from six archaeological sites in France dated from the 14th to 19th centuries AD. Dental calculus was demonstrated by macroscopic and cone-beam observations. In 56 calculus specimens free of PCR inhibition, PCR sequencing identified Candidatus Methanobrevibacter sp. N13 in 44.6%, Methanobrevibacter oralis in 19.6%, a new Methanomassiliicoccus luminyensis-like methanogen in 12.5%, a Candidatus Nitrososphaera evergladensis-like in one and Methanoculleus bourgensis in one specimen, respectively. One Candidatus Methanobrevibacter sp. N13 dental calculus was further documented by fluorescent in situ hybridization. The prevalence of dental calculus M. oralis was significantly lower in past populations than in modern populations (P = 0.03, Chi-square test). This investigation revealed a previously unknown repertoire of archaea found in the oral cavity of past French populations as reflected in preserved dental calculus.
Highlights
We aimed to confirm the presence of dental calculus in the sample under investigation
Among these 56 dental calculus specimens, 42 (75%) were positive for methanogen DNA evidenced by a 16S rRNA gene sequence in 40 (71.4%) samples and by a mcrA sequence in 28 (50%) samples
Phylogenetic analysis further indicated that calculus specimens P27, 138, 142 and 486 contained three 350– 550-bp M. luminyensis-like sequences
Summary
We aimed to confirm the presence of dental calculus in the sample under investigation. A Candidatus Nitrososphaera evergladensis-like methanogen was found in one specimen at site A, while M. bourgensis was observed in one calculus specimen obtained from the 19th century site C. M. luminyensis-like, M. bourgensis and a Candidatus Nitrososphaera evergladensis-like methanogen found in the historic French samples included in the current study have never been detected in modern populations (Fig. 3). It appears that regardless of the method used for the detection of methanogens in the dental plaque, the prevalence and diversity of methanogens in dental calculus have decreased significantly over the course of the past seven centuries. Understanding these factors is of interest as methanogens, and M. oralis, have been implicated in periodontitis, a disease with major nutritional consequences in certain populations such as elderly people[18]
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