Fig. 1. Saliva collection study design.

Each subject provided two saliva samples at the same time, one collected alone and the other collected using the Spectrum sDNA-1000 kit which includes a sample preservative. The order in which samples were collected was randomized between subjects. The six subjects who provided two longitudinal samples provided the second sample the day following their initial saliva sample, using the same collection protocol with samples collected in the same order as on the previous day. For metagenomic studies, we assessed the effects of a protocol to deplete human DNA, using only samples in which the original preservative was used (n = 14 samples). We compared results in which the depletion technique was used or not; for six of the samples, DNA quantity was insufficient for metagenomics, so eight were studied in all.