Small RNA sequencing of plasma RNA. Homo sapiens

We report the sequencing of small RNAs present in the plasma of three normal subjects. In addition to microRNAs we identified abundant non-human small RNA sequences. The organisms from which these were derived were identified by BLAST searches with contigs assembled from the short sequences. The taxonomic profiles were very consistent between individuals, including plants and microbes reported previously in the microbiome, but in proportions distinct from other sites. The majority of bacterial reads were from the phylum Proteobacteria, whilst for 5 of 6 individuals over 90% of the more abundant fungal reads were from the phylum Ascomycota; of these over 90% were from the order Hypocreales. Most reads mapped to rRNA sequences and the presence of specific common sequences was confirmed by RT-PCR. In addition, extremely abundant small RNAs derived from human Y RNAs were detected. We conclude that a characteristic profile of a subset of the human microbiome can be obtained by sequencing small RNAs present in the blood. The origin and potential function of these molecules remains to be determined, but the specific profile is likely to reflect health status. This facile test has immense potential to provide biomarkers for the diagnosis and prognosis of human disease. Overall design: The profile of small RNAs present in the plasma of three normal subjects was determined