Diurnal oscillations in human salivary microRNA and microbial transcription

We investigated daily oscillations in salivary miRNA and microbial RNA to explore relationships between these components of the gut-brain-axis and their implications in human health. Nine subjects provided 120 saliva samples at designated times, on repeated days. Samples were divided into three sets for exploration and cross-validation. Identification and quantification of host miRNA and microbial RNA was performed using next generation sequencing. Eleven miRNAs and 11 microbial RNAs demonstrated consistent diurnal oscillation across the first 2 sample sets and accurately predicted collection time in the hold-out set based on multivariate logistic regression modeling. Associations among five circadian miRNAs and four circadian microbial RNAs were observed. Salivary miRNA and microbial taxon profiles of 120 human samples were generated by shotgun sequencing, using Illumina NextSeq 500.