The Salivary Mycobiome Contains 2 Ecologically Distinct Mycotypes

A broad range of fungi has been detected in molecular surveys of the oral mycobiome. However, knowledge is still lacking on interindividual variability of these communities and the ecologic and clinical significance of oral fungal commensals. In this cross-sectional study, we use internal transcribed spacer 1 amplicon sequencing to evaluate the salivary mycobiome in 59 subjects, 36 of whom were scheduled to receive cancer chemotherapy. Analysis of the broad population structure of fungal communities in the whole cohort identified 2 well-demarcated genus-level community types (mycotypes), with Candida and Malassezia as the main taxa driving cluster partitioning. The Candida mycotype had lower diversity than the Malassezia mycotype and was positively correlated with cancer and steroid use in these subjects, smoking, caries, utilizing a removable prosthesis, and plaque index. Mycotypes were also associated with metabolically distinct bacteria indicative of divergent oral environments, with aciduric species enriched in the Candida mycotype and inflammophilic bacteria increased in the Malassezia mycotype. Similar to their fungal counterparts, coexisting bacterial communities associated with the Candida mycotype showed lower diversity than those associated with the Malassezia mycotype, suggesting that common environmental pressures affected bacteria and fungi. Mycotypes were also seen in an independent cohort of 24 subjects, in which cultivation revealed Malassezia as viable oral mycobiome members, although the low-abundance Malassezia sympodialis was the only Malassezia species recovered. There was a high degree of concordance between the molecular detection and cultivability of Candida, while cultivation showed low sensitivity for detection of the Malassezia mycotype. Overall, our work provides insights into the oral mycobiome landscape, revealing 2 community classes with apparently distinct ecologic constraints and specific associations with coexisting bacteria and clinical parameters. The utility of mycotypes as biomarkers for oral diseases warrants further study.

Using high throughput sequencing to explore the biodiversity in oral bacterial communities

High throughput sequencing of 16S ribosomal RNA gene amplicons is a cost-effective method for characterization of oral bacterial communities. However, before undertaking large-scale studies, it is necessary to understand the technique-associated limitations and intrinsic variability of the oral ecosystem. In this work we evaluated bias in species representation using an in vitro-assembled mock community of oral bacteria. We then characterized the bacterial communities in saliva and buccal mucosa of five healthy subjects to investigate the power of high throughput sequencing in revealing their diversity and biogeography patterns. Mock community analysis showed primer and DNA isolation biases and an overestimation of diversity that was reduced after eliminating singleton operational taxonomic units (OTUs). Sequencing of salivary and mucosal communities found a total of 455 OTUs (0.3% dissimilarity) with only 78 of these present in all subjects. We demonstrate that this variability was partly the result of incomplete richness coverage even at great sequencing depths, and so comparing communities by their structure was more effective than comparisons based solely on membership. With respect to oral biogeography, we found inter-subject variability in community structure was lower than site differences between salivary and mucosal communities within subjects. These differences were evident at very low sequencing depths and were mostly caused by the abundance of Streptococcus mitis and Gemella haemolysans in mucosa. In summary, we present an experimental and data analysis framework that will facilitate design and interpretation of pyrosequencing-based studies. Despite challenges associated with this technique, we demonstrate its power for evaluation of oral diversity and biogeography patterns.

Calcium and magnesium utilization in rats: effect of dietary butterfat and calcium and of age

This factorial study was designed to examine the effect of short- and long-term ingestion of dietary calcium (0.25% and 1.0%) and butterfat (5% and 20%) and treatment with dimethylhydrazine (DMH) in rats. Calcium, magnesium and phosphorus absorption and, to a lesser extent, total diet digestibility decreased as the rats aged from 2 to 8 mo. Increased ingestion of butterfat had no effect on apparent absorption of calcium among young rats but tended to decrease calcium absorption in mature rats. The weak effect (P less than 0.05) of butterfat on calcium absorption reflected the small amount of calcium (less than 2% of fecal calcium) associated with lipids in feces. Ingestion of 10 vs. 2.5 mg Ca/g diet reduced the efficiency of apparent absorption of calcium, magnesium and phosphorus of young and mature rats and resulted in slightly, but significantly, greater retention of calcium in bone after 27 wk. The total amounts of calcium retained in tibias were correlated with the amounts of calcium absorbed by rats after 4, but not after 27, wk of dietary treatments. Rats dosed with DMH exhibited improved efficiency of calcium absorption, but the incidence of intestinal tumors did not affect mineral utilization.