Viruses are the unknown studied members of the gut microbiome. A new metagenomic analysis in healthy adults reveals that fecal viruses show a high stability, individual specificity, and correlation with the bacterial microbiome for 1 year.

Besides bacteria, researchers have begun to study archaea, fungi, protozoa and viruses of the human gut microbiome. Although it is now known that the human gut microbiome contains several viruses, most of which are bacteriaphages, little is known about the human gut virome partly due to limitations in analyzing the fecal virome with the current metagenomic and bioinformatic protocols and technology. In fact, the human gut virome has been called “viral dark matter” because taxonomic classification of bacterial viruses is largely unknown due to the high inter-individual variation of species, lack of a universal gene marker like 16S ribosomal ribonucleic acid (rRNA) for bacteria, and viral databases that are largely incomplete.